751290 - Firefox cannot play part of a webm video

Status: RESOLVED WORKSFORME

(Core :: Audio/Video, defect)

Description

[Thang]

User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.19 (KHTML, like Gecko) Chrome/18.0.1025.162 Safari/535.19

Steps to reproduce:

Tried to play a webm video...

Encoded a video from h264 to vpx via ffmpeg, compiled per these instructions: 
http://ubuntuforums.org/showpost.php?p=9868359&postcount=1289

The command looks like so:

ffmpeg -y -i test.mov -threads 4 -f webm -vcodec libvpx -filter:v yadif -g 120 -level 216 -profile 0 -qmax 42 -qmin 10 -rc_buf_aggressivity 0.95 -vb 2M -acodec libvorbis -aq 70 -ac 2 test.webm


Actual results:

The first 5 seconds are unavailable for playback, however seeking past that yields expected results. 

Video played back fine in VLC/Chrome, but not Firefox[12.0] on Win7 64bit/Ubuntu 10.04/OSX 10.7.


Expected results:

The entire video should be playable, not just after 5 seconds. 

The troublesome file can be found here:
http://ec2-75-101-179-22.compute-1.amazonaws.com/projects/test/.alternates/Zero_Table_Top_Showreel_2010_ffox.webm
The original source file here:
http://ec2-75-101-179-22.compute-1.amazonaws.com/projects/test/Zero_Table_Top_Showreel_2010.mov

Other webm videos are able to play back, just not this one. While I'm torn between placing the blame on ffmpeg/libvpx or Firefox, the fact that this video is able to play in Chrome and VLC leads me to believe this is more a Firefox issue.

Comment 1

[Alice0775 White]

Confirmed in Nightly15.0a1
http://hg.mozilla.org/mozilla-central/rev/b13bfc70bc44
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:15.0) Gecko/15.0 Firefox/15.0a1 ID:20120502030505

This can reproduce in Firefox 4.0.1-Aurora13.0a2.

Comment 2

[Matthew Gregan [:kinetik]]

It seems like an ffmpeg bug.  mkvinfo -v shows:

|+ Cluster
| + Cluster timecode: 0.000s
| + SimpleBlock (key, track number 2, 1 frame(s), timecode 18446744027.136s = 00:00:00.-03)
| + SimpleBlock (key, track number 1, 1 frame(s), timecode 0.000s = 00:00:00.000)

Note the negative timecode for the first (audio) block.  Firefox treats negative timecodes as an error, so decoding stops immediately after processing this block and the media is treated as if it has reached the end of the stream.

It plays in Opera.  Presumably Chrome/VLC/Opera treat the negative timecode as zero.

Comment 3

[Thang]

Cheers for that catch Matthew, I've managed to workaround this, ironically with ffmpeg:

ffmpeg -y -fflags +genpts -i Zero_Table_Top_Showreel_2010_ffox.webm -itsoffset 0.3 -i Zero_Table_Top_Showreel_2010_ffox.webm -map 0:0 -map 1:1 -vcodec copy -acodec copy -f webm "output.webm" 

The output webm plays fine, mkvinfo -v no longer shows a negative time code and the command runs very quickly. 

For now, I'm going to run with this solution. 

Thanks

Comment 4

[Matthew Gregan [:kinetik]]

Thanks for filing the bug.  Glad you found a workaround.  Looking at the new commandline, and the output from ffmpeg when encoding the file, the problem is actually in the original file.  The new commandline avoids the problem by skipping the part of the input with the invalid timecode.

Still, it seems wrong that ffmpeg generates an invalid WebM file because of that.  It might be worth filing a bug against ffmpeg and see what they say: https://ffmpeg.org/trac/ffmpeg