[Spice-devel] [spice-html5 audio 2/4] Revise sound packet time sequencing for a more recent Firefox.

[Jeremy White]

Around version 45, Firefox started being very particular about the
time stamps put into the Opus stream.  The time stamps from the Spice server are
somewhat irregular.  They mostly arrive every 10 ms, but sometimes it is 11, or sometimes
with two time stamps the same in a row.  The previous logic resulted in fuzzy and/or
distorted audio streams in Firefox in a row.

Thus, we end up with an inelegant hack.  Essentially, we force every packet to have
a 10ms time delta, unless there is an obvious gap in time stream, in which case we
will resync.

This replaces logic that mitigated only the duplicated time packets.

The long term solution would appear to be 'sequence' mode, but I cannot get
Firefox to use that mode (and MDN suggests that for codecs such as VP8 with time
stamps in line, that Firefox will not accept it).

Signed-off-by: Jeremy White <jwhite at codeweavers.com>
---
 playback.js | 38 ++++++++++++++++++++++++++++----------
 webm.js     |  1 +
 2 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/playback.js b/playback.js
index 1d89719..f10a071 100644
--- a/playback.js
+++ b/playback.js
@@ -89,15 +89,6 @@ SpicePlaybackConn.prototype.process_channel_message = function(msg)
     {
         var data = new SpiceMsgPlaybackData(msg.data);
 
-        // If this packet has the same time as the last, just bump up by one.
-        if (this.last_data_time && data.time <= this.last_data_time)
-        {
-            // FIXME - this is arguably wrong.  But delaying the transmission was worse,
-            //          in initial testing.  Could use more research.
-            PLAYBACK_DEBUG > 1 && console.log("Hacking time of " + data.time + " to " + this.last_data_time + 1);
-            data.time = this.last_data_time + 1;
-        }
-
         if (! this.source_buffer)
             return true;
 
@@ -110,8 +101,35 @@ SpicePlaybackConn.prototype.process_channel_message = function(msg)
             this.audio.currentTime = this.audio.buffered.start(this.audio.buffered.length - 1);
         }
 
-        this.last_data_time = data.time;
+        /* Around version 45, Firefox started being very particular about the
+           time stamps put into the Opus stream.  The time stamps from the Spice server are
+           somewhat irregular.  They mostly arrive every 10 ms, but sometimes it is 11, or sometimes
+           with two time stamps the same in a row.  The previous logic resulted in fuzzy and/or
+           distorted audio streams in Firefox in a row.
+
+           In theory, the sequence mode should be appropriate for us, but as of 09/27/2016,
+           I was unable to make sequence mode work with Firefox.
 
+           Thus, we end up with an inelegant hack.  Essentially, we force every packet to have
+           a 10ms time delta, unless there is an obvious gap in time stream, in which case we
+           will resync.
+        */
+
+        if (this.start_time != 0 && data.time != (this.last_data_time + EXPECTED_PACKET_DURATION))
+        {
+            if (Math.abs(data.time - (EXPECTED_PACKET_DURATION + this.last_data_time)) < MAX_CLUSTER_TIME)
+            {
+                PLAYBACK_DEBUG > 1 && console.log("Hacking time of " + data.time + " to " +
+                                      (this.last_data_time + EXPECTED_PACKET_DURATION));
+                data.time = this.last_data_time + EXPECTED_PACKET_DURATION;
+            }
+            else
+            {
+                PLAYBACK_DEBUG > 1 && console.log("Apparent gap in audio time; now is " + data.time + " last was " + this.last_data_time);
+            }
+        }
+
+        this.last_data_time = data.time;
 
         PLAYBACK_DEBUG > 1 && console.log("PlaybackData; time " + data.time + "; length " + data.data.byteLength);
 
diff --git a/webm.js b/webm.js
index 8faa8e7..789da14 100644
--- a/webm.js
+++ b/webm.js
@@ -84,6 +84,7 @@ var OPUS_CHANNELS                           = 2;
 var SPICE_PLAYBACK_CODEC                    = 'audio/webm; codecs="opus"';
 var MAX_CLUSTER_TIME                        = 1000;
 
+var EXPECTED_PACKET_DURATION                = 10;
 var GAP_DETECTION_THRESHOLD                 = 50;
 
 var SPICE_VP8_CODEC                         = 'video/webm; codecs="vp8"';
-- 
2.1.4