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+vivid: Virtual Video Test Driver
+================================
+
+This driver emulates video4linux hardware of various types: video capture, video
+output, vbi capture and output, radio receivers and transmitters and a software
+defined radio receiver. In addition a simple framebuffer device is available for
+testing capture and output overlays.
+
+Up to 64 vivid instances can be created, each with up to 16 inputs and 16 outputs.
+
+Each input can be a webcam, TV capture device, S-Video capture device or an HDMI
+capture device. Each output can be an S-Video output device or an HDMI output
+device.
+
+These inputs and outputs act exactly as a real hardware device would behave. This
+allows you to use this driver as a test input for application development, since
+you can test the various features without requiring special hardware.
+
+This document describes the features implemented by this driver:
+
+- Support for read()/write(), MMAP, USERPTR and DMABUF streaming I/O.
+- A large list of test patterns and variations thereof
+- Working brightness, contrast, saturation and hue controls
+- Support for the alpha color component
+- Full colorspace support, including limited/full RGB range
+- All possible control types are present
+- Support for various pixel aspect ratios and video aspect ratios
+- Error injection to test what happens if errors occur
+- Supports crop/compose/scale in any combination for both input and output
+- Can emulate up to 4K resolutions
+- All Field settings are supported for testing interlaced capturing
+- Supports all standard YUV and RGB formats, including two multiplanar YUV formats
+- Raw and Sliced VBI capture and output support
+- Radio receiver and transmitter support, including RDS support
+- Software defined radio (SDR) support
+- Capture and output overlay support
+
+These features will be described in more detail below.
+
+
+Table of Contents
+-----------------
+
+Section 1: Configuring the driver
+Section 2: Video Capture
+Section 2.1: Webcam Input
+Section 2.2: TV and S-Video Inputs
+Section 2.3: HDMI Input
+Section 3: Video Output
+Section 3.1: S-Video Output
+Section 3.2: HDMI Output
+Section 4: VBI Capture
+Section 5: VBI Output
+Section 6: Radio Receiver
+Section 7: Radio Transmitter
+Section 8: Software Defined Radio Receiver
+Section 9: Controls
+Section 9.1: User Controls - Test Controls
+Section 9.2: User Controls - Video Capture
+Section 9.3: User Controls - Audio
+Section 9.4: Vivid Controls
+Section 9.4.1: Test Pattern Controls
+Section 9.4.2: Capture Feature Selection Controls
+Section 9.4.3: Output Feature Selection Controls
+Section 9.4.4: Error Injection Controls
+Section 9.4.5: VBI Raw Capture Controls
+Section 9.5: Digital Video Controls
+Section 9.6: FM Radio Receiver Controls
+Section 9.7: FM Radio Modulator
+Section 10: Video, VBI and RDS Looping
+Section 10.1: Video and Sliced VBI looping
+Section 10.2: Radio & RDS Looping
+Section 11: Cropping, Composing, Scaling
+Section 12: Formats
+Section 13: Capture Overlay
+Section 14: Output Overlay
+Section 15: Some Future Improvements
+
+
+Section 1: Configuring the driver
+---------------------------------
+
+By default the driver will create a single instance that has a video capture
+device with webcam, TV, S-Video and HDMI inputs, a video output device with
+S-Video and HDMI outputs, one vbi capture device, one vbi output device, one
+radio receiver device, one radio transmitter device and one SDR device.
+
+The number of instances, devices, video inputs and outputs and their types are
+all configurable using the following module options:
+
+n_devs: number of driver instances to create. By default set to 1. Up to 64
+	instances can be created.
+
+node_types: which devices should each driver instance create. An array of
+	hexadecimal values, one for each instance. The default is 0x1d3d.
+	Each value is a bitmask with the following meaning:
+		bit 0: Video Capture node
+		bit 2-3: VBI Capture node: 0 = none, 1 = raw vbi, 2 = sliced vbi, 3 = both
+		bit 4: Radio Receiver node
+		bit 5: Software Defined Radio Receiver node
+		bit 8: Video Output node
+		bit 10-11: VBI Output node: 0 = none, 1 = raw vbi, 2 = sliced vbi, 3 = both
+		bit 12: Radio Transmitter node
+		bit 16: Framebuffer for testing overlays
+
+	So to create four instances, the first two with just one video capture
+	device, the second two with just one video output device you would pass
+	these module options to vivid:
+
+		n_devs=4 node_types=0x1,0x1,0x100,0x100
+
+num_inputs: the number of inputs, one for each instance. By default 4 inputs
+	are created for each video capture device. At most 16 inputs can be created,
+	and there must be at least one.
+
+input_types: the input types for each instance, the default is 0xe4. This defines
+	what the type of each input is when the inputs are created for each driver
+	instance. This is a hexadecimal value with up to 16 pairs of bits, each
+	pair gives the type and bits 0-1 map to input 0, bits 2-3 map to input 1,
+	30-31 map to input 15. Each pair of bits has the following meaning:
+
+		00: this is a webcam input
+		01: this is a TV tuner input
+		10: this is an S-Video input
+		11: this is an HDMI input
+
+	So to create a video capture device with 8 inputs where input 0 is a TV
+	tuner, inputs 1-3 are S-Video inputs and inputs 4-7 are HDMI inputs you
+	would use the following module options:
+
+		num_inputs=8 input_types=0xffa9
+
+num_outputs: the number of outputs, one for each instance. By default 2 outputs
+	are created for each video output device. At most 16 outputs can be
+	created, and there must be at least one.
+
+output_types: the output types for each instance, the default is 0x02. This defines
+	what the type of each output is when the outputs are created for each
+	driver instance. This is a hexadecimal value with up to 16 bits, each bit
+	gives the type and bit 0 maps to output 0, bit 1 maps to output 1, bit
+	15 maps to output 15. The meaning of each bit is as follows:
+
+		0: this is an S-Video output
+		1: this is an HDMI output
+
+	So to create a video output device with 8 outputs where outputs 0-3 are
+	S-Video outputs and outputs 4-7 are HDMI outputs you would use the
+	following module options:
+
+		num_outputs=8 output_types=0xf0
+
+vid_cap_nr: give the desired videoX start number for each video capture device.
+	The default is -1 which will just take the first free number. This allows
+	you to map capture video nodes to specific videoX device nodes. Example:
+
+		n_devs=4 vid_cap_nr=2,4,6,8
+
+	This will attempt to assign /dev/video2 for the video capture device of
+	the first vivid instance, video4 for the next up to video8 for the last
+	instance. If it can't succeed, then it will just take the next free
+	number.
+
+vid_out_nr: give the desired videoX start number for each video output device.
+        The default is -1 which will just take the first free number.
+
+vbi_cap_nr: give the desired vbiX start number for each vbi capture device.
+        The default is -1 which will just take the first free number.
+
+vbi_out_nr: give the desired vbiX start number for each vbi output device.
+        The default is -1 which will just take the first free number.
+
+radio_rx_nr: give the desired radioX start number for each radio receiver device.
+        The default is -1 which will just take the first free number.
+
+radio_tx_nr: give the desired radioX start number for each radio transmitter
+	device. The default is -1 which will just take the first free number.
+
+sdr_cap_nr: give the desired swradioX start number for each SDR capture device.
+        The default is -1 which will just take the first free number.
+
+ccs_cap_mode: specify the allowed video capture crop/compose/scaling combination
+	for each driver instance. Video capture devices can have any combination
+	of cropping, composing and scaling capabilities and this will tell the
+	vivid driver which of those is should emulate. By default the user can
+	select this through controls.
+
+	The value is either -1 (controlled by the user) or a set of three bits,
+	each enabling (1) or disabling (0) one of the features:
+
+		bit 0: Enable crop support. Cropping will take only part of the
+		       incoming picture.
+		bit 1: Enable compose support. Composing will copy the incoming
+		       picture into a larger buffer.
+		bit 2: Enable scaling support. Scaling can scale the incoming
+		       picture. The scaler of the vivid driver can enlarge up
+		       or down to four times the original size. The scaler is
+		       very simple and low-quality. Simplicity and speed were
+		       key, not quality.
+
+	Note that this value is ignored by webcam inputs: those enumerate
+	discrete framesizes and that is incompatible with cropping, composing
+	or scaling.
+
+ccs_out_mode: specify the allowed video output crop/compose/scaling combination
+	for each driver instance. Video output devices can have any combination
+	of cropping, composing and scaling capabilities and this will tell the
+	vivid driver which of those is should emulate. By default the user can
+	select this through controls.
+
+	The value is either -1 (controlled by the user) or a set of three bits,
+	each enabling (1) or disabling (0) one of the features:
+
+		bit 0: Enable crop support. Cropping will take only part of the
+		       outgoing buffer.
+		bit 1: Enable compose support. Composing will copy the incoming
+		       buffer into a larger picture frame.
+		bit 2: Enable scaling support. Scaling can scale the incoming
+		       buffer. The scaler of the vivid driver can enlarge up
+		       or down to four times the original size. The scaler is
+		       very simple and low-quality. Simplicity and speed were
+		       key, not quality.
+
+multiplanar: select whether each device instance supports multi-planar formats,
+	and thus the V4L2 multi-planar API. By default the first device instance
+	is single-planar, the second multi-planar, and it keeps alternating.
+
+	This module option can override that for each instance. Values are:
+
+		0: use alternating single and multi-planar devices.
+		1: this is a single-planar instance.
+		2: this is a multi-planar instance.
+
+vivid_debug: enable driver debugging info
+
+no_error_inj: if set disable the error injecting controls. This option is
+	needed in order to run a tool like v4l2-compliance. Tools like that
+	exercise all controls including a control like 'Disconnect' which
+	emulates a USB disconnect, making the device inaccessible and so
+	all tests that v4l2-compliance is doing will fail afterwards.
+
+	There may be other situations as well where you want to disable the
+	error injection support of vivid. When this option is set, then the
+	controls that select crop, compose and scale behavior are also
+	removed. Unless overridden by ccs_cap_mode and/or ccs_out_mode the
+	will default to enabling crop, compose and scaling.
+
+Taken together, all these module options allow you to precisely customize
+the driver behavior and test your application with all sorts of permutations.
+It is also very suitable to emulate hardware that is not yet available, e.g.
+when developing software for a new upcoming device.
+
+
+Section 2: Video Capture
+------------------------
+
+This is probably the most frequently used feature. The video capture device
+can be configured by using the module options num_inputs, input_types and
+ccs_cap_mode (see section 1 for more detailed information), but by default
+four inputs are configured: a webcam, a TV tuner, an S-Video and an HDMI
+input, one input for each input type. Those are described in more detail
+below.
+
+Special attention has been given to the rate at which new frames become
+available. The jitter will be around 1 jiffie (that depends on the HZ
+configuration of your kernel, so usually 1/100, 1/250 or 1/1000 of a second),
+but the long-term behavior is exactly following the framerate. So a
+framerate of 59.94 Hz is really different from 60 Hz. If the framerate
+exceeds your kernel's HZ value, then you will get dropped frames, but the
+frame/field sequence counting will keep track of that so the sequence
+count will skip whenever frames are dropped.
+
+
+Section 2.1: Webcam Input
+-------------------------
+
+The webcam input supports three framesizes: 320x180, 640x360 and 1280x720. It
+supports frames per second settings of 10, 15, 25, 30, 50 and 60 fps. Which ones
+are available depends on the chosen framesize: the larger the framesize, the
+lower the maximum frames per second.
+
+The initially selected colorspace when you switch to the webcam input will be
+sRGB.
+
+
+Section 2.2: TV and S-Video Inputs
+----------------------------------
+
+The only difference between the TV and S-Video input is that the TV has a
+tuner. Otherwise they behave identically.
+
+These inputs support audio inputs as well: one TV and one Line-In. They
+both support all TV standards. If the standard is queried, then the Vivid
+controls 'Standard Signal Mode' and 'Standard' determine what
+the result will be.
+
+These inputs support all combinations of the field setting. Special care has
+been taken to faithfully reproduce how fields are handled for the different
+TV standards. This is particularly noticable when generating a horizontally
+moving image so the temporal effect of using interlaced formats becomes clearly
+visible. For 50 Hz standards the top field is the oldest and the bottom field
+is the newest in time. For 60 Hz standards that is reversed: the bottom field
+is the oldest and the top field is the newest in time.
+
+When you start capturing in V4L2_FIELD_ALTERNATE mode the first buffer will
+contain the top field for 50 Hz standards and the bottom field for 60 Hz
+standards. This is what capture hardware does as well.
+
+Finally, for PAL/SECAM standards the first half of the top line contains noise.
+This simulates the Wide Screen Signal that is commonly placed there.
+
+The initially selected colorspace when you switch to the TV or S-Video input
+will be SMPTE-170M.
+
+The pixel aspect ratio will depend on the TV standard. The video aspect ratio
+can be selected through the 'Standard Aspect Ratio' Vivid control.
+Choices are '4x3', '16x9' which will give letterboxed widescreen video and
+'16x9 Anomorphic' which will give full screen squashed anamorphic widescreen
+video that will need to be scaled accordingly.
+
+The TV 'tuner' supports a frequency range of 44-958 MHz. Channels are available
+every 6 MHz, starting from 49.25 MHz. For each channel the generated image
+will be in color for the +/- 0.25 MHz around it, and in grayscale for
++/- 1 MHz around the channel. Beyond that it is just noise. The VIDIOC_G_TUNER
+ioctl will return 100% signal strength for +/- 0.25 MHz and 50% for +/- 1 MHz.
+It will also return correct afc values to show whether the frequency is too
+low or too high.
+
+The audio subchannels that are returned are MONO for the +/- 1 MHz range around
+a valid channel frequency. When the frequency is within +/- 0.25 MHz of the
+channel it will return either MONO, STEREO, either MONO | SAP (for NTSC) or
+LANG1 | LANG2 (for others), or STEREO | SAP.
+
+Which one is returned depends on the chosen channel, each next valid channel
+will cycle through the possible audio subchannel combinations. This allows
+you to test the various combinations by just switching channels..
+
+Finally, for these inputs the v4l2_timecode struct is filled in in the
+dequeued v4l2_buffer struct.
+
+
+Section 2.3: HDMI Input
+-----------------------
+
+The HDMI inputs supports all CEA-861 and DMT timings, both progressive and
+interlaced, for pixelclock frequencies between 25 and 600 MHz. The field
+mode for interlaced formats is always V4L2_FIELD_ALTERNATE. For HDMI the
+field order is always top field first, and when you start capturing an
+interlaced format you will receive the top field first.
+
+The initially selected colorspace when you switch to the HDMI input or
+select an HDMI timing is based on the format resolution: for resolutions
+less than or equal to 720x576 the colorspace is set to SMPTE-170M, for
+others it is set to REC-709 (CEA-861 timings) or sRGB (VESA DMT timings).
+
+The pixel aspect ratio will depend on the HDMI timing: for 720x480 is it
+set as for the NTSC TV standard, for 720x576 it is set as for the PAL TV
+standard, and for all others a 1:1 pixel aspect ratio is returned.
+
+The video aspect ratio can be selected through the 'DV Timings Aspect Ratio'
+Vivid control. Choices are 'Source Width x Height' (just use the
+same ratio as the chosen format), '4x3' or '16x9', either of which can
+result in pillarboxed or letterboxed video.
+
+For HDMI inputs it is possible to set the EDID. By default a simple EDID
+is provided. You can only set the EDID for HDMI inputs. Internally, however,
+the EDID is shared between all HDMI inputs.
+
+No interpretation is done of the EDID data.
+
+
+Section 3: Video Output
+-----------------------
+
+The video output device can be configured by using the module options
+num_outputs, output_types and ccs_out_mode (see section 1 for more detailed
+information), but by default two outputs are configured: an S-Video and an
+HDMI input, one output for each output type. Those are described in more detail
+below.
+
+Like with video capture the framerate is also exact in the long term.
+
+
+Section 3.1: S-Video Output
+---------------------------
+
+This output supports audio outputs as well: "Line-Out 1" and "Line-Out 2".
+The S-Video output supports all TV standards.
+
+This output supports all combinations of the field setting.
+
+The initially selected colorspace when you switch to the TV or S-Video input
+will be SMPTE-170M.
+
+
+Section 3.2: HDMI Output
+------------------------
+
+The HDMI output supports all CEA-861 and DMT timings, both progressive and
+interlaced, for pixelclock frequencies between 25 and 600 MHz. The field
+mode for interlaced formats is always V4L2_FIELD_ALTERNATE.
+
+The initially selected colorspace when you switch to the HDMI output or
+select an HDMI timing is based on the format resolution: for resolutions
+less than or equal to 720x576 the colorspace is set to SMPTE-170M, for
+others it is set to REC-709 (CEA-861 timings) or sRGB (VESA DMT timings).
+
+The pixel aspect ratio will depend on the HDMI timing: for 720x480 is it
+set as for the NTSC TV standard, for 720x576 it is set as for the PAL TV
+standard, and for all others a 1:1 pixel aspect ratio is returned.
+
+An HDMI output has a valid EDID which can be obtained through VIDIOC_G_EDID.
+
+
+Section 4: VBI Capture
+----------------------
+
+There are three types of VBI capture devices: those that only support raw
+(undecoded) VBI, those that only support sliced (decoded) VBI and those that
+support both. This is determined by the node_types module option. In all
+cases the driver will generate valid VBI data: for 60 Hz standards it will
+generate Closed Caption and XDS data. The closed caption stream will
+alternate between "Hello world!" and "Closed captions test" every second.
+The XDS stream will give the current time once a minute. For 50 Hz standards
+it will generate the Wide Screen Signal which is based on the actual Video
+Aspect Ratio control setting.
+
+The VBI device will only work for the S-Video and TV inputs, it will give
+back an error if the current input is a webcam or HDMI.
+
+
+Section 5: VBI Output
+---------------------
+
+There are three types of VBI output devices: those that only support raw
+(undecoded) VBI, those that only support sliced (decoded) VBI and those that
+support both. This is determined by the node_types module option.
+
+The sliced VBI output supports the Wide Screen Signal for 50 Hz standards
+and Closed Captioning + XDS for 60 Hz standards.
+
+The VBI device will only work for the S-Video output, it will give
+back an error if the current output is HDMI.
+
+
+Section 6: Radio Receiver
+-------------------------
+
+The radio receiver emulates an FM/AM/SW receiver. The FM band also supports RDS.
+The frequency ranges are:
+
+	FM: 64 MHz - 108 MHz
+	AM: 520 kHz - 1710 kHz
+	SW: 2300 kHz - 26.1 MHz
+
+Valid channels are emulated every 1 MHz for FM and every 100 kHz for AM and SW.
+The signal strength decreases the further the frequency is from the valid
+frequency until it becomes 0% at +/- 50 kHz (FM) or 5 kHz (AM/SW) from the
+ideal frequency. The initial frequency when the driver is loaded is set to
+95 MHz.
+
+The FM receiver supports RDS as well, both using 'Block I/O' and 'Controls'
+modes. In the 'Controls' mode the RDS information is stored in read-only
+controls. These controls are updated every time the frequency is changed,
+or when the tuner status is requested. The Block I/O method uses the read()
+interface to pass the RDS blocks on to the application for decoding.
+
+The RDS signal is 'detected' for +/- 12.5 kHz around the channel frequency,
+and the further the frequency is away from the valid frequency the more RDS
+errors are randomly introduced into the block I/O stream, up to 50% of all
+blocks if you are +/- 12.5 kHz from the channel frequency. All four errors
+can occur in equal proportions: blocks marked 'CORRECTED', blocks marked
+'ERROR', blocks marked 'INVALID' and dropped blocks.
+
+The generated RDS stream contains all the standard fields contained in a
+0B group, and also radio text and the current time.
+
+The receiver supports HW frequency seek, either in Bounded mode, Wrap Around
+mode or both, which is configurable with the "Radio HW Seek Mode" control.
+
+
+Section 7: Radio Transmitter
+----------------------------
+
+The radio transmitter emulates an FM/AM/SW transmitter. The FM band also supports RDS.
+The frequency ranges are:
+
+	FM: 64 MHz - 108 MHz
+	AM: 520 kHz - 1710 kHz
+	SW: 2300 kHz - 26.1 MHz
+
+The initial frequency when the driver is loaded is 95.5 MHz.
+
+The FM transmitter supports RDS as well, both using 'Block I/O' and 'Controls'
+modes. In the 'Controls' mode the transmitted RDS information is configured
+using controls, and in 'Block I/O' mode the blocks are passed to the driver
+using write().
+
+
+Section 8: Software Defined Radio Receiver
+------------------------------------------
+
+The SDR receiver has three frequency bands for the ADC tuner:
+
+	- 300 kHz
+	- 900 kHz - 2800 kHz
+	- 3200 kHz
+
+The RF tuner supports 50 MHz - 2000 MHz.
+
+The generated data contains the In-phase and Quadrature components of a
+1 kHz tone that has an amplitude of sqrt(2).
+
+
+Section 9: Controls
+-------------------
+
+Different devices support different controls. The sections below will describe
+each control and which devices support them.
+
+
+Section 9.1: User Controls - Test Controls
+------------------------------------------
+
+The Button, Boolean, Integer 32 Bits, Integer 64 Bits, Menu, String, Bitmask and
+Integer Menu are controls that represent all possible control types. The Menu
+control and the Integer Menu control both have 'holes' in their menu list,
+meaning that one or more menu items return EINVAL when VIDIOC_QUERYMENU is called.
+Both menu controls also have a non-zero minimum control value.  These features
+allow you to check if your application can handle such things correctly.
+These controls are supported for every device type.
+
+
+Section 9.2: User Controls - Video Capture
+------------------------------------------
+
+The following controls are specific to video capture.
+
+The Brightness, Contrast, Saturation and Hue controls actually work and are
+standard. There is one special feature with the Brightness control: each
+video input has its own brightness value, so changing input will restore
+the brightness for that input. In addition, each video input uses a different
+brightness range (minimum and maximum control values). Switching inputs will
+cause a control event to be sent with the V4L2_EVENT_CTRL_CH_RANGE flag set.
+This allows you to test controls that can change their range.
+
+The 'Gain, Automatic' and Gain controls can be used to test volatile controls:
+if 'Gain, Automatic' is set, then the Gain control is volatile and changes
+constantly. If 'Gain, Automatic' is cleared, then the Gain control is a normal
+control.
+
+The 'Horizontal Flip' and 'Vertical Flip' controls can be used to flip the
+image. These combine with the 'Sensor Flipped Horizontally/Vertically' Vivid
+controls.
+
+The 'Alpha Component' control can be used to set the alpha component for
+formats containing an alpha channel.
+
+
+Section 9.3: User Controls - Audio
+----------------------------------
+
+The following controls are specific to video capture and output and radio
+receivers and transmitters.
+
+The 'Volume' and 'Mute' audio controls are typical for such devices to
+control the volume and mute the audio. They don't actually do anything in
+the vivid driver.
+
+
+Section 9.4: Vivid Controls
+---------------------------
+
+These vivid custom controls control the image generation, error injection, etc.
+
+
+Section 9.4.1: Test Pattern Controls
+------------------------------------
+
+The Test Pattern Controls are all specific to video capture.
+
+Test Pattern: selects which test pattern to use. Use the CSC Colorbar for
+	testing colorspace conversions: the colors used in that test pattern
+	map to valid colors in all colorspaces. The colorspace conversion
+	is disabled for the other test patterns.
+
+OSD Text Mode: selects whether the text superimposed on the
+	test pattern should be shown, and if so, whether only counters should
+	be displayed or the full text.
+
+Horizontal Movement: selects whether the test pattern should
+	move to the left or right and at what speed.
+
+Vertical Movement: does the same for the vertical direction.
+
+Show Border: show a two-pixel wide border at the edge of the actual image,
+	excluding letter or pillarboxing.
+
+Show Square: show a square in the middle of the image. If the image is
+	displayed with the correct pixel and image aspect ratio corrections,
+	then the width and height of the square on the monitor should be
+	the same.
+
+Insert SAV Code in Image: adds a SAV (Start of Active Video) code to the image.
+	This can be used to check if such codes in the image are inadvertently
+	interpreted instead of being ignored.
+
+Insert EAV Code in Image: does the same for the EAV (End of Active Video) code.
+
+
+Section 9.4.2: Capture Feature Selection Controls
+-------------------------------------------------
+
+These controls are all specific to video capture.
+
+Sensor Flipped Horizontally: the image is flipped horizontally and the
+	V4L2_IN_ST_HFLIP input status flag is set. This emulates the case where
+	a sensor is for example mounted upside down.
+
+Sensor Flipped Vertically: the image is flipped vertically and the
+	V4L2_IN_ST_VFLIP input status flag is set. This emulates the case where
+        a sensor is for example mounted upside down.
+
+Standard Aspect Ratio: selects if the image aspect ratio as used for the TV or
+	S-Video input should be 4x3, 16x9 or anamorphic widescreen. This may
+	introduce letterboxing.
+
+DV Timings Aspect Ratio: selects if the image aspect ratio as used for the HDMI
+	input should be the same as the source width and height ratio, or if
+	it should be 4x3 or 16x9. This may introduce letter or pillarboxing.
+
+Timestamp Source: selects when the timestamp for each buffer is taken.
+
+Colorspace: selects which colorspace should be used when generating the image.
+	This only applies if the CSC Colorbar test pattern is selected,
+	otherwise the test pattern will go through unconverted (except for
+	the so-called 'Transfer Function' corrections and the R'G'B' to Y'CbCr
+	conversion). This behavior is also what you want, since a 75% Colorbar
+	should really have 75% signal intensity and should not be affected
+	by colorspace conversions.
+
+	Changing the colorspace will result in the V4L2_EVENT_SOURCE_CHANGE
+	to be sent since it emulates a detected colorspace change.
+
+Limited RGB Range (16-235): selects if the RGB range of the HDMI source should
+	be limited or full range. This combines with the Digital Video 'Rx RGB
+	Quantization Range' control and can be used to test what happens if
+	a source provides you with the wrong quantization range information.
+	See the description of that control for more details.
+
+Apply Alpha To Red Only: apply the alpha channel as set by the 'Alpha Component'
+	user control to the red color of the test pattern only.
+
+Enable Capture Cropping: enables crop support. This control is only present if
+	the ccs_cap_mode module option is set to the default value of -1 and if
+	the no_error_inj module option is set to 0 (the default).
+
+Enable Capture Composing: enables composing support. This control is only
+	present if the ccs_cap_mode module option is set to the default value of
+	-1 and if the no_error_inj module option is set to 0 (the default).
+
+Enable Capture Scaler: enables support for a scaler (maximum 4 times upscaling
+	and downscaling). This control is only present if the ccs_cap_mode
+	module option is set to the default value of -1 and if the no_error_inj
+	module option is set to 0 (the default).
+
+Maximum EDID Blocks: determines how many EDID blocks the driver supports.
+	Note that the vivid driver does not actually interpret new EDID
+	data, it just stores it. It allows for up to 256 EDID blocks
+	which is the maximum supported by the standard.
+
+Fill Percentage of Frame: can be used to draw only the top X percent
+	of the image. Since each frame has to be drawn by the driver, this
+	demands a lot of the CPU. For large resolutions this becomes
+	problematic. By drawing only part of the image this CPU load can
+	be reduced.
+
+
+Section 9.4.3: Output Feature Selection Controls
+------------------------------------------------
+
+These controls are all specific to video output.
+
+Enable Output Cropping: enables crop support. This control is only present if
+	the ccs_out_mode module option is set to the default value of -1 and if
+	the no_error_inj module option is set to 0 (the default).
+
+Enable Output Composing: enables composing support. This control is only
+	present if the ccs_out_mode module option is set to the default value of
+	-1 and if the no_error_inj module option is set to 0 (the default).
+
+Enable Output Scaler: enables support for a scaler (maximum 4 times upscaling
+	and downscaling). This control is only present if the ccs_out_mode
+	module option is set to the default value of -1 and if the no_error_inj
+	module option is set to 0 (the default).
+
+
+Section 9.4.4: Error Injection Controls
+---------------------------------------
+
+The following two controls are only valid for video and vbi capture.
+
+Standard Signal Mode: selects the behavior of VIDIOC_QUERYSTD: what should
+	it return?
+
+	Changing this control will result in the V4L2_EVENT_SOURCE_CHANGE
+	to be sent since it emulates a changed input condition (e.g. a cable
+	was plugged in or out).
+
+Standard: selects the standard that VIDIOC_QUERYSTD should return if the
+	previous control is set to "Selected Standard".
+
+	Changing this control will result in the V4L2_EVENT_SOURCE_CHANGE
+	to be sent since it emulates a changed input standard.
+
+
+The following two controls are only valid for video capture.
+
+DV Timings Signal Mode: selects the behavior of VIDIOC_QUERY_DV_TIMINGS: what
+	should it return?
+
+	Changing this control will result in the V4L2_EVENT_SOURCE_CHANGE
+	to be sent since it emulates a changed input condition (e.g. a cable
+	was plugged in or out).
+
+DV Timings: selects the timings the VIDIOC_QUERY_DV_TIMINGS should return
+	if the previous control is set to "Selected DV Timings".
+
+	Changing this control will result in the V4L2_EVENT_SOURCE_CHANGE
+	to be sent since it emulates changed input timings.
+
+
+The following controls are only present if the no_error_inj module option
+is set to 0 (the default). These controls are valid for video and vbi
+capture and output streams and for the SDR capture device except for the
+Disconnect control which is valid for all devices.
+
+Wrap Sequence Number: test what happens when you wrap the sequence number in
+	struct v4l2_buffer around.
+
+Wrap Timestamp: test what happens when you wrap the timestamp in struct
+	v4l2_buffer around.
+
+Percentage of Dropped Buffers: sets the percentage of buffers that
+	are never returned by the driver (i.e., they are dropped).
+
+Disconnect: emulates a USB disconnect. The device will act as if it has
+	been disconnected. Only after all open filehandles to the device
+	node have been closed will the device become 'connected' again.
+
+Inject V4L2_BUF_FLAG_ERROR: when pressed, the next frame returned by
+	the driver will have the error flag set (i.e. the frame is marked
+	corrupt).
+
+Inject VIDIOC_REQBUFS Error: when pressed, the next REQBUFS or CREATE_BUFS
+	ioctl call will fail with an error. To be precise: the videobuf2
+	queue_setup() op will return -EINVAL.
+
+Inject VIDIOC_QBUF Error: when pressed, the next VIDIOC_QBUF or
+	VIDIOC_PREPARE_BUFFER ioctl call will fail with an error. To be
+	precise: the videobuf2 buf_prepare() op will return -EINVAL.
+
+Inject VIDIOC_STREAMON Error: when pressed, the next VIDIOC_STREAMON ioctl
+	call will fail with an error. To be precise: the videobuf2
+	start_streaming() op will return -EINVAL.
+
+Inject Fatal Streaming Error: when pressed, the streaming core will be
+	marked as having suffered a fatal error, the only way to recover
+	from that is to stop streaming. To be precise: the videobuf2
+	vb2_queue_error() function is called.
+
+
+Section 9.4.5: VBI Raw Capture Controls
+---------------------------------------
+
+Interlaced VBI Format: if set, then the raw VBI data will be interlaced instead
+	of providing it grouped by field.
+
+
+Section 9.5: Digital Video Controls
+-----------------------------------
+
+Rx RGB Quantization Range: sets the RGB quantization detection of the HDMI
+	input. This combines with the Vivid 'Limited RGB Range (16-235)'
+	control and can be used to test what happens if a source provides
+	you with the wrong quantization range information. This can be tested
+	by selecting an HDMI input, setting this control to Full or Limited
+	range and selecting the opposite in the 'Limited RGB Range (16-235)'
+	control. The effect is easy to see if the 'Gray Ramp' test pattern
+	is selected.
+
+Tx RGB Quantization Range: sets the RGB quantization detection of the HDMI
+	output. It is currently not used for anything in vivid, but most HDMI
+	transmitters would typically have this control.
+
+Transmit Mode: sets the transmit mode of the HDMI output to HDMI or DVI-D. This
+	affects the reported colorspace since DVI_D outputs will always use
+	sRGB.
+
+
+Section 9.6: FM Radio Receiver Controls
+---------------------------------------
+
+RDS Reception: set if the RDS receiver should be enabled.
+
+RDS Program Type:
+RDS PS Name:
+RDS Radio Text:
+RDS Traffic Announcement:
+RDS Traffic Program:
+RDS Music: these are all read-only controls. If RDS Rx I/O Mode is set to
+	"Block I/O", then they are inactive as well. If RDS Rx I/O Mode is set
+	to "Controls", then these controls report the received RDS data. Note
+	that the vivid implementation of this is pretty basic: they are only
+	updated when you set a new frequency or when you get the tuner status
+	(VIDIOC_G_TUNER).
+
+Radio HW Seek Mode: can be one of "Bounded", "Wrap Around" or "Both". This
+	determines if VIDIOC_S_HW_FREQ_SEEK will be bounded by the frequency
+	range or wrap-around or if it is selectable by the user.
+
+Radio Programmable HW Seek: if set, then the user can provide the lower and
+	upper bound of the HW Seek. Otherwise the frequency range boundaries
+	will be used.
+
+Generate RBDS Instead of RDS: if set, then generate RBDS (the US variant of
+	RDS) data instead of RDS (European-style RDS). This affects only the
+	PICODE and PTY codes.
+
+RDS Rx I/O Mode: this can be "Block I/O" where the RDS blocks have to be read()
+	by the application, or "Controls" where the RDS data is provided by
+	the RDS controls mentioned above.
+
+
+Section 9.7: FM Radio Modulator Controls
+----------------------------------------
+
+RDS Program ID:
+RDS Program Type:
+RDS PS Name:
+RDS Radio Text:
+RDS Stereo:
+RDS Artificial Head:
+RDS Compressed:
+RDS Dymanic PTY:
+RDS Traffic Announcement:
+RDS Traffic Program:
+RDS Music: these are all controls that set the RDS data that is transmitted by
+	the FM modulator.
+
+RDS Tx I/O Mode: this can be "Block I/O" where the application has to use write()
+	to pass the RDS blocks to the driver, or "Controls" where the RDS data is
+	provided by the RDS controls mentioned above.
+
+
+Section 10: Video, VBI and RDS Looping
+--------------------------------------
+
+The vivid driver supports looping of video output to video input, VBI output
+to VBI input and RDS output to RDS input. For video/VBI looping this emulates
+as if a cable was hooked up between the output and input connector. So video
+and VBI looping is only supported between S-Video and HDMI inputs and outputs.
+VBI is only valid for S-Video as it makes no sense for HDMI.
+
+Since radio is wireless this looping always happens if the radio receiver
+frequency is close to the radio transmitter frequency. In that case the radio
+transmitter will 'override' the emulated radio stations.
+
+Looping is currently supported only between devices created by the same
+vivid driver instance.
+
+
+Section 10.1: Video and Sliced VBI looping
+------------------------------------------
+
+The way to enable video/VBI looping is currently fairly crude. A 'Loop Video'
+control is available in the "Vivid" control class of the video
+output and VBI output devices. When checked the video looping will be enabled.
+Once enabled any video S-Video or HDMI input will show a static test pattern
+until the video output has started. At that time the video output will be
+looped to the video input provided that:
+
+- the input type matches the output type. So the HDMI input cannot receive
+  video from the S-Video output.
+
+- the video resolution of the video input must match that of the video output.
+  So it is not possible to loop a 50 Hz (720x576) S-Video output to a 60 Hz
+  (720x480) S-Video input, or a 720p60 HDMI output to a 1080p30 input.
+
+- the pixel formats must be identical on both sides. Otherwise the driver would
+  have to do pixel format conversion as well, and that's taking things too far.
+
+- the field settings must be identical on both sides. Same reason as above:
+  requiring the driver to convert from one field format to another complicated
+  matters too much. This also prohibits capturing with 'Field Top' or 'Field
+  Bottom' when the output video is set to 'Field Alternate'. This combination,
+  while legal, became too complicated to support. Both sides have to be 'Field
+  Alternate' for this to work. Also note that for this specific case the
+  sequence and field counting in struct v4l2_buffer on the capture side may not
+  be 100% accurate.
+
+- on the input side the "Standard Signal Mode" for the S-Video input or the
+  "DV Timings Signal Mode" for the HDMI input should be configured so that a
+  valid signal is passed to the video input.
+
+The framerates do not have to match, although this might change in the future.
+
+By default you will see the OSD text superimposed on top of the looped video.
+This can be turned off by changing the "OSD Text Mode" control of the video
+capture device.
+
+For VBI looping to work all of the above must be valid and in addition the vbi
+output must be configured for sliced VBI. The VBI capture side can be configured
+for either raw or sliced VBI.
+
+
+Section 10.2: Radio & RDS Looping
+---------------------------------
+
+As mentioned in section 6 the radio receiver emulates stations are regular
+frequency intervals. Depending on the frequency of the radio receiver a
+signal strength value is calculated (this is returned by VIDIOC_G_TUNER).
+However, it will also look at the frequency set by the radio transmitter and
+if that results in a higher signal strength than the settings of the radio
+transmitter will be used as if it was a valid station. This also includes
+the RDS data (if any) that the transmitter 'transmits'. This is received
+faithfully on the receiver side. Note that when the driver is loaded the
+frequencies of the radio receiver and transmitter are not identical, so
+initially no looping takes place.
+
+
+Section 11: Cropping, Composing, Scaling
+----------------------------------------
+
+This driver supports cropping, composing and scaling in any combination. Normally
+which features are supported can be selected through the Vivid controls,
+but it is also possible to hardcode it when the module is loaded through the
+ccs_cap_mode and ccs_out_mode module options. See section 1 on the details of
+these module options.
+
+This allows you to test your application for all these variations.
+
+Note that the webcam input never supports cropping, composing or scaling. That
+only applies to the TV/S-Video/HDMI inputs and outputs. The reason is that
+webcams, including this virtual implementation, normally use
+VIDIOC_ENUM_FRAMESIZES to list a set of discrete framesizes that it supports.
+And that does not combine with cropping, composing or scaling. This is
+primarily a limitation of the V4L2 API which is carefully reproduced here.
+
+The minimum and maximum resolutions that the scaler can achieve are 16x16 and
+(4096 * 4) x (2160 x 4), but it can only scale up or down by a factor of 4 or
+less. So for a source resolution of 1280x720 the minimum the scaler can do is
+320x180 and the maximum is 5120x2880. You can play around with this using the
+qv4l2 test tool and you will see these dependencies.
+
+This driver also supports larger 'bytesperline' settings, something that
+VIDIOC_S_FMT allows but that few drivers implement.
+
+The scaler is a simple scaler that uses the Coarse Bresenham algorithm. It's
+designed for speed and simplicity, not quality.
+
+If the combination of crop, compose and scaling allows it, then it is possible
+to change crop and compose rectangles on the fly.
+
+
+Section 12: Formats
+-------------------
+
+The driver supports all the regular packed YUYV formats, 16, 24 and 32 RGB
+packed formats and two multiplanar formats (one luma and one chroma plane).
+
+The alpha component can be set through the 'Alpha Component' User control
+for those formats that support it. If the 'Apply Alpha To Red Only' control
+is set, then the alpha component is only used for the color red and set to
+0 otherwise.
+
+The driver has to be configured to support the multiplanar formats. By default
+the first driver instance is single-planar, the second is multi-planar, and it
+keeps alternating. This can be changed by setting the multiplanar module option,
+see section 1 for more details on that option.
+
+If the driver instance is using the multiplanar formats/API, then the first
+single planar format (YUYV) and the multiplanar NV16M and NV61M formats the
+will have a plane that has a non-zero data_offset of 128 bytes. It is rare for
+data_offset to be non-zero, so this is a useful feature for testing applications.
+
+Video output will also honor any data_offset that the application set.
+
+
+Section 13: Capture Overlay
+---------------------------
+
+Note: capture overlay support is implemented primarily to test the existing
+V4L2 capture overlay API. In practice few if any GPUs support such overlays
+anymore, and neither are they generally needed anymore since modern hardware
+is so much more capable. By setting flag 0x10000 in the node_types module
+option the vivid driver will create a simple framebuffer device that can be
+used for testing this API. Whether this API should be used for new drivers is
+questionable.
+
+This driver has support for a destructive capture overlay with bitmap clipping
+and list clipping (up to 16 rectangles) capabilities. Overlays are not
+supported for multiplanar formats. It also honors the struct v4l2_window field
+setting: if it is set to FIELD_TOP or FIELD_BOTTOM and the capture setting is
+FIELD_ALTERNATE, then only the top or bottom fields will be copied to the overlay.
+
+The overlay only works if you are also capturing at that same time. This is a
+vivid limitation since it copies from a buffer to the overlay instead of
+filling the overlay directly. And if you are not capturing, then no buffers
+are available to fill.
+
+In addition, the pixelformat of the capture format and that of the framebuffer
+must be the same for the overlay to work. Otherwise VIDIOC_OVERLAY will return
+an error.
+
+In order to really see what it going on you will need to create two vivid
+instances: the first with a framebuffer enabled. You configure the capture
+overlay of the second instance to use the framebuffer of the first, then
+you start capturing in the second instance. For the first instance you setup
+the output overlay for the video output, turn on video looping and capture
+to see the blended framebuffer overlay that's being written to by the second
+instance. This setup would require the following commands:
+
+	$ sudo modprobe vivid n_devs=2 node_types=0x10101,0x1 multiplanar=1,1
+	$ v4l2-ctl -d1 --find-fb
+	/dev/fb1 is the framebuffer associated with base address 0x12800000
+	$ sudo v4l2-ctl -d2 --set-fbuf fb=1
+	$ v4l2-ctl -d1 --set-fbuf fb=1
+	$ v4l2-ctl -d0 --set-fmt-video=pixelformat='AR15'
+	$ v4l2-ctl -d1 --set-fmt-video-out=pixelformat='AR15'
+	$ v4l2-ctl -d2 --set-fmt-video=pixelformat='AR15'
+	$ v4l2-ctl -d0 -i2
+	$ v4l2-ctl -d2 -i2
+	$ v4l2-ctl -d2 -c horizontal_movement=4
+	$ v4l2-ctl -d1 --overlay=1
+	$ v4l2-ctl -d1 -c loop_video=1
+	$ v4l2-ctl -d2 --stream-mmap --overlay=1
+
+And from another console:
+
+	$ v4l2-ctl -d1 --stream-out-mmap
+
+And yet another console:
+
+	$ qv4l2
+
+and start streaming.
+
+As you can see, this is not for the faint of heart...
+
+
+Section 14: Output Overlay
+--------------------------
+
+Note: output overlays are primarily implemented in order to test the existing
+V4L2 output overlay API. Whether this API should be used for new drivers is
+questionable.
+
+This driver has support for an output overlay and is capable of:
+
+	- bitmap clipping,
+	- list clipping (up to 16 rectangles)
+	- chromakey
+	- source chromakey
+	- global alpha
+	- local alpha
+	- local inverse alpha
+
+Output overlays are not supported for multiplanar formats. In addition, the
+pixelformat of the capture format and that of the framebuffer must be the
+same for the overlay to work. Otherwise VIDIOC_OVERLAY will return an error.
+
+Output overlays only work if the driver has been configured to create a
+framebuffer by setting flag 0x10000 in the node_types module option. The
+created framebuffer has a size of 720x576 and supports ARGB 1:5:5:5 and
+RGB 5:6:5.
+
+In order to see the effects of the various clipping, chromakeying or alpha
+processing capabilities you need to turn on video looping and see the results
+on the capture side. The use of the clipping, chromakeying or alpha processing
+capabilities will slow down the video loop considerably as a lot of checks have
+to be done per pixel.
+
+
+Section 15: Some Future Improvements
+------------------------------------
+
+Just as a reminder and in no particular order:
+
+- Add a virtual alsa driver to test audio
+- Add virtual sub-devices and media controller support
+- Some support for testing compressed video
+- Add support to loop raw VBI output to raw VBI input
+- Fix sequence/field numbering when looping of video with alternate fields
+- Add support for V4L2_CID_BG_COLOR for video outputs
+- Add ARGB888 overlay support: better testing of the alpha channel
+- Add custom DV timings support
+- Add support for V4L2_DV_FL_REDUCED_FPS
+- Improve pixel aspect support in the tpg code by passing a real v4l2_fract
+- Use per-queue locks and/or per-device locks to improve throughput
+- Add support to loop from a specific output to a specific input across
+  vivid instances
+- Add support for VIDIOC_EXPBUF once support for that has been added to vb2
+- The SDR radio should use the same 'frequencies' for stations as the normal
+  radio receiver, and give back noise if the frequency doesn't match up with
+  a station frequency
+- Improve the sine generation of the SDR radio.
+- Make a thread for the RDS generation, that would help in particular for the
+  "Controls" RDS Rx I/O Mode as the read-only RDS controls could be updated
+  in real-time.
