[Spice-devel] [spice-html5 audio 1/4] Use modern brower information to detect underrun.

[Jeremy White]

We previously had a fairly crude 'gap detection', but browsers
are largely supporting the modern buffer semantics, and we can
now rely on them to detect under runs for us.

This improves audio in Chrome while playing large videos.

Signed-off-by: Jeremy White <jwhite at codeweavers.com>
---
 playback.js | 30 ++++++++----------------------
 1 file changed, 8 insertions(+), 22 deletions(-)

diff --git a/playback.js b/playback.js
index e5f4661..1d89719 100644
--- a/playback.js
+++ b/playback.js
@@ -29,8 +29,6 @@ function SpicePlaybackConn()
     this.queue = new Array();
     this.append_okay = false;
     this.start_time = 0;
-    this.skip_until = 0;
-    this.gap_time = 0;
 }
 
 SpicePlaybackConn.prototype = Object.create(SpiceConn.prototype);
@@ -103,19 +101,13 @@ SpicePlaybackConn.prototype.process_channel_message = function(msg)
         if (! this.source_buffer)
             return true;
 
-        /* Gap detection:  If there has been a delay since our last packet, then audio must
-             have paused.  Handling that gets tricky.  In Chrome, you can seek forward,
-             but you cannot in Firefox.  And seeking forward in Chrome is nice, as it keeps
-             Chrome from being overly cautious in it's buffer strategy.
-
-             So we do two things.  First, we seek forward.  Second, we compute how much of a gap
-             there would have been, and essentially eliminate it.
-        */
-        if (this.last_data_time && data.time >= (this.last_data_time + GAP_DETECTION_THRESHOLD))
+        if (this.audio.readyState >= 3 && this.audio.buffered.length > 1 &&
+            this.audio.currentTime == this.audio.buffered.end(0) &&
+            this.audio.currentTime < this.audio.buffered.start(this.audio.buffered.length - 1))
         {
-            this.skip_until = data.time;
-            this.gap_time = (data.time - this.start_time) -
-              (this.source_buffer.buffered.end(this.source_buffer.buffered.end.length - 1) * 1000.0).toFixed(0);
+            console.log("Audio underrun: we appear to have fallen behind; advancing to " +
+                this.audio.buffered.start(this.audio.buffered.length - 1));
+            this.audio.currentTime = this.audio.buffered.start(this.audio.buffered.length - 1);
         }
 
         this.last_data_time = data.time;
@@ -126,18 +118,12 @@ SpicePlaybackConn.prototype.process_channel_message = function(msg)
         if (this.start_time == 0)
             this.start_playback(data);
 
-        else if (data.time - this.cluster_time >= MAX_CLUSTER_TIME || this.skip_until > 0)
+        else if (data.time - this.cluster_time >= MAX_CLUSTER_TIME)
             this.new_cluster(data);
 
         else
             this.simple_block(data, false);
 
-        if (this.skip_until > 0)
-        {
-            this.audio.currentTime = (this.skip_until - this.start_time - this.gap_time) / 1000.0;
-            this.skip_until = 0;
-        }
-
         if (this.audio.paused)
             this.audio.play();
 
@@ -205,7 +191,7 @@ SpicePlaybackConn.prototype.new_cluster = function(data)
 {
     this.cluster_time = data.time;
 
-    var c = new webm_Cluster(data.time - this.start_time - this.gap_time);
+    var c = new webm_Cluster(data.time - this.start_time);
 
     var mb = new ArrayBuffer(c.buffer_size());
     this.bytes_written += c.to_buffer(mb);
-- 
2.1.4