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bug: Out of sync subtitles with mod_h264_streaming Created Apr 6, 2009

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Views: 2557     Replies: 5     Last reply Apr 12, 2009  
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mspasov

Posts: 6

Registered:
Apr 6, 2009

bug: Out of sync subtitles with mod_h264_streaming

Posted: Apr 6, 2009

Hello,

I have located a bug in pseudostreaming, that is the root all evil^H^H^H^H problems with timeline sync when scrubbing with mod_h264_streaming and pseudostreaming. After some email exchanges with the mod_h264_streaming developer we found out that the problem is somewhere in Flowplayer.

Here is my test case setup:
  • A video with overlay-ed accurate timestamp and frame numbers.
  • Subtitles with timestamp displayed every second.
  • Flowplayer 3.0.7 with flowplayer.pseudostreaming-3.1.1
  • mod_h264_streaming 2.0 with lighttpd 1.5

What I do:
I'm playing the video with the subtitles and when I scrub to time x, flowplayer.pseudostream finds the nearest keyframe x+n, and makes a request to x+n, however the time in the player stays x, and we have video playing from time x+n with drift n. Subsequent seeks makes the drift worse, usualy about 250 frames (maximum Pseudostreaming gives correct keyframe positions - x+n is at a keyframe. This is very annoying when watching closed captioned video, because subtitles are sync-ed to the x timeline.

I think the bug is trivial to fix, but hard to hit and probably causes some other problems.

Workaround (realy realy not recommended):
Until fixed, movies could be encoded with smaller max GOP size (default is 250 or around 10 sec in a 25 fps video), however this will lower the quality and enlarge the moov atom. Do this only as a last resort..

If additional information is needed, I'll be more than happy to provide it.

mspasov

Posts: 6

Registered:
Apr 6, 2009

Patch to fix this..

Posted: Apr 8, 2009

Reply to: bug: Out of sync subtitles with mod_h264_streaming, from mspasov
This fixes about 90% of the sync issues, I'll continue to dig further. It's tested only with mp4, it's possible that this breaks flv!

ps. it's my first touch with flex/as and such, I'm sure that there is more elegant and 'correct' way to do this.


Index: pseudostreaming/src/actionscript/org/flowplayer/pseudostreaming/DefaultSeekDataStore.as
===================================================================
--- pseudostreaming/src/actionscript/org/flowplayer/pseudostreaming/DefaultSeekDataStore.as	(revision 363)
+++ pseudostreaming/src/actionscript/org/flowplayer/pseudostreaming/DefaultSeekDataStore.as	(working copy)
@@ -65,7 +65,10 @@
         if (!rangeEnd) {
             rangeEnd = _keyFrameTimes.length - 1;
         }
-        if (rangeBegin == rangeEnd) return queryParamValue(rangeBegin);
+        if (rangeBegin == rangeEnd) {
+		 prevSeekTime=_keyFrameTimes[rangeBegin];
+		 return queryParamValue(rangeBegin);
+	}
 
         var rangeMid:Number = Math.floor((rangeEnd + rangeBegin)/2);
         if (_keyFrameTimes[rangeMid] >= seekPosition)

mspasov

Posts: 6

Registered:
Apr 6, 2009

And another one..

Posted: Apr 9, 2009

Reply to: bug: Out of sync subtitles with mod_h264_streaming, from mspasov
Ok, here is another one. Seems to fix the rest 10% of incorrect time sync. Probably it's a border case, caused by incorrect rounding of the meta data either in flowplayer or in mod_h264_streaming..


--- PseudoStreamProvider.as 
+++ PseudoStreamProvider.as.old 
@@ -130,7 +130,7 @@
     }
 
     private function appendQueryString(url:String, start:Number):String {
-        return url + _config.queryString.replace("${start}", start == 0 ? 0 : _seekDataStore.getQueryStringStartValue(start));
+        return url + _config.queryString.replace("${start}", start == 0 ? 0 : (_seekDataStore.getQueryStringStartValue(start)+0.01));
     }
 
     override protected function onMetaData(event:ClipEvent):void {

Anssi
Flowplayer Flash & video streaming developer

Posts: 1194

Registered:
Jul 24, 2007

» bug: Out of sync subtitles with mod_h264_streaming

Posted: Apr 9, 2009

Reply to: bug: Out of sync subtitles with mod_h264_streaming, from mspasov
Thanks for investigating this. I've applied these changes (changed the internal implementation a bit) to the trunk version of the plugin. You can find the changes in SVN at google code.

mspasov

Posts: 6

Registered:
Apr 6, 2009

Thank you for fixing this.

Posted: Apr 9, 2009

Reply to: » bug: Out of sync subtitles with mod_h264_streaming, from Anssi
Thank you for fixing this. I have updated to head, but I'm unable to compile it. It seems HEAD is broken (or I'm missing something):


compile-lib:
     [exec] Loading configuration file /home/avatar/flex_sdk_3/frameworks/flex-config.xml
     [exec] /home/avatar/work-flowplayer-svn/flowplayer/src/actionscript/org/flowplayer/view/RotatingAnimation.as(25): col: 36 Error: Type was not found or was not a compile-time constant: BufferAnimation.
     [exec] 
     [exec]         private var _rotationImage:BufferAnimation;
     [exec]                                    ^
     [exec] 
     [exec] /home/avatar/work-flowplayer-svn/flowplayer/src/actionscript/org/flowplayer/view/RotatingAnimation.as(53): col: 34 Error: Call to a possibly undefined method BufferAnimation.
     [exec] 
     [exec]             _rotationImage = new BufferAnimation();
     [exec]                                  ^
     [exec] 
     [exec] Result: 2

I'm at r189 in core and r368 in plugins.

Anssi
Flowplayer Flash & video streaming developer

Posts: 1194

Registered:
Jul 24, 2007

» Thank you for fixing this.

Posted: Apr 12, 2009

Reply to: Thank you for fixing this., from mspasov
A fixed build.xml is now committed and it should compile.