[v2,3/6] vnc: h264: send additional frames after the display is clean

Commit Message

Dietmar Maurer April 10, 2025, 11:22 a.m. UTC

The H264 implementation only sends frames when it detects changes in
the server's framebuffer. This leads to artifacts when there are no
further changes, as the internal H264 encoder may still contain data.

This patch modifies the code to send a few additional frames in such
situations to flush the H264 encoder data.

Signed-off-by: Dietmar Maurer <[e-mail]>
---
 ui/vnc.c | 25 ++++++++++++++++++++++++-
 ui/vnc.h |  3 +++
 2 files changed, 27 insertions(+), 1 deletion(-)

Patch

diff --git a/ui/vnc.c b/ui/vnc.c
index 2e60b55e47..4ba0b715fd 100644
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -3239,7 +3239,30 @@  static void vnc_refresh(DisplayChangeListener *dcl)
     vnc_unlock_display(vd);
 
     QTAILQ_FOREACH_SAFE(vs, &vd->clients, next, vn) {
-        rects += vnc_update_client(vs, has_dirty);
+        int client_dirty = has_dirty;
+        if (vs->h264) {
+            if (client_dirty) {
+                vs->h264->keep_dirty = VNC_H264_KEEP_DIRTY;
+            } else {
+                if (vs->h264->keep_dirty > 0) {
+                    client_dirty = 1;
+                    vs->h264->keep_dirty--;
+                }
+            }
+        }
+
+        int count = vnc_update_client(vs, client_dirty);
+        rects += count;
+
+        if (vs->h264 && !count && vs->h264->keep_dirty) {
+            VncJob *job = vnc_job_new(vs);
+            int height = pixman_image_get_height(vd->server);
+            int width = pixman_image_get_width(vd->server);
+            vs->job_update = vs->update;
+            vs->update = VNC_STATE_UPDATE_NONE;
+            vnc_job_add_rect(job, 0, 0, width, height);
+            vnc_job_push(job);
+        }
         /* vs might be free()ed here */
     }
 
diff --git a/ui/vnc.h b/ui/vnc.h
index 7e232f7dac..e1b81d6bcc 100644
--- a/ui/vnc.h
+++ b/ui/vnc.h
@@ -236,10 +236,13 @@  typedef struct VncZywrle {
 } VncZywrle;
 
 #ifdef CONFIG_GSTREAMER
+/* Number of frames we send after the display is clean. */
+#define VNC_H264_KEEP_DIRTY 10
 typedef struct VncH264 {
     GstElement *pipeline, *source, *gst_encoder, *sink, *convert;
     size_t width;
     size_t height;
+    guint keep_dirty;
 } VncH264;
 #endif