[Spice-devel] [spice-gtk] RFC: Allow to limit the latency introduced by lip sync

[Frediano Ziglio]

This patch allows to reduce the time the client wait to display frames.
It can make the lip sync not working but it allows to see the
video latency introduced by this code.
This patch is meant to be used mainly for debugging:
- recently we are seeing some artifacts due to this delay and
  overlaying, removing the delay make easier to understand if the
  problem is related to this or other issues;
- we are testing guest encoding and we are experiencing a big lag.
  This avoid this part of the lag helping understand where the other
  part of the delay happens.

Signed-off-by: Frediano Ziglio <fziglio at redhat.com>
---
This patch is not intended to be merged as is but to be used to fix
above problems or as a start for some better settings.
---
 src/channel-display-gst.c   | 10 ++++++----
 src/channel-display-mjpeg.c | 24 +++++++++++++++++++-----
 src/channel-display-priv.h  |  3 +++
 3 files changed, 28 insertions(+), 9 deletions(-)

Changes since last version:
- rebased on master.

It seems is still useful, still not clear all sync process.

diff --git a/src/channel-display-gst.c b/src/channel-display-gst.c
index f978602..9ee6229 100644
--- a/src/channel-display-gst.c
+++ b/src/channel-display-gst.c
@@ -173,8 +173,10 @@ static void schedule_frame(SpiceGstDecoder *decoder)
             break;
         }
 
-        if (spice_mmtime_diff(now, gstframe->frame->mm_time) < 0) {
-            decoder->timer_id = g_timeout_add(gstframe->frame->mm_time - now,
+        gint32 time_diff = spice_mmtime_diff(gstframe->frame->mm_time, now);
+        time_diff = MIN(time_diff, max_frame_delay_ms);
+        if (time_diff > 0) {
+            decoder->timer_id = g_timeout_add(time_diff,
                                               display_frame, decoder);
         } else if (g_queue_get_length(decoder->display_queue) == 1) {
             /* Still attempt to display the least out of date frame so the
@@ -182,8 +184,8 @@ static void schedule_frame(SpiceGstDecoder *decoder)
              */
             decoder->timer_id = g_timeout_add(0, display_frame, decoder);
         } else {
-            SPICE_DEBUG("%s: rendering too late by %u ms (ts: %u, mmtime: %u), dropping",
-                        __FUNCTION__, now - gstframe->frame->mm_time,
+            SPICE_DEBUG("%s: rendering too late by %d ms (ts: %u, mmtime: %u), dropping",
+                        __FUNCTION__, -time_diff,
                         gstframe->frame->mm_time, now);
             stream_dropped_frame_on_playback(decoder->base.stream);
             g_queue_pop_head(decoder->display_queue);
diff --git a/src/channel-display-mjpeg.c b/src/channel-display-mjpeg.c
index f0d55f6..cc9ddf1 100644
--- a/src/channel-display-mjpeg.c
+++ b/src/channel-display-mjpeg.c
@@ -189,6 +189,19 @@ static gboolean mjpeg_decoder_decode_frame(gpointer video_decoder)
 
 /* ---------- VideoDecoder's queue scheduling ---------- */
 
+enum { MAX_DELAY_MS = 2000 };
+gint32 max_frame_delay_ms = MAX_DELAY_MS;
+
+SPICE_CONSTRUCTOR_FUNC(max_delay_init)
+{
+    const char *str_delay = g_getenv("SPICE_MAX_FRAME_DELAY");
+    if (str_delay) {
+        int delay = atoi(str_delay);
+        if (delay >= 0 && delay <= MAX_DELAY_MS)
+            max_frame_delay_ms = delay;
+    }
+}
+
 static void mjpeg_decoder_schedule(MJpegDecoder *decoder)
 {
     SPICE_DEBUG("%s", __FUNCTION__);
@@ -201,15 +214,16 @@ static void mjpeg_decoder_schedule(MJpegDecoder *decoder)
     decoder->cur_frame = NULL;
     do {
         if (frame) {
-            if (spice_mmtime_diff(time, frame->mm_time) <= 0) {
-                guint32 d = frame->mm_time - time;
+            gint32 time_diff = spice_mmtime_diff(frame->mm_time, time);
+            time_diff = MIN(time_diff, max_frame_delay_ms);
+            if (time_diff >= 0) {
                 decoder->cur_frame = frame;
-                decoder->timer_id = g_timeout_add(d, mjpeg_decoder_decode_frame, decoder);
+                decoder->timer_id = g_timeout_add(time_diff, mjpeg_decoder_decode_frame, decoder);
                 break;
             }
 
-            SPICE_DEBUG("%s: rendering too late by %u ms (ts: %u, mmtime: %u), dropping ",
-                        __FUNCTION__, time - frame->mm_time,
+            SPICE_DEBUG("%s: rendering too late by %d ms (ts: %u, mmtime: %u), dropping ",
+                        __FUNCTION__, -time_diff,
                         frame->mm_time, time);
             stream_dropped_frame_on_playback(decoder->base.stream);
             free_spice_frame(frame);
diff --git a/src/channel-display-priv.h b/src/channel-display-priv.h
index 1389868..92bd85a 100644
--- a/src/channel-display-priv.h
+++ b/src/channel-display-priv.h
@@ -197,6 +197,9 @@ void stream_display_frame(display_stream *st, SpiceFrame *frame, uint32_t width,
 gint64 get_stream_id_by_stream(SpiceChannel *channel, display_stream *st);
 
 
+/* maximum delay for frames */
+extern gint32 max_frame_delay_ms;
+
 G_END_DECLS
 
 #endif // CHANNEL_DISPLAY_PRIV_H_
-- 
2.13.5