Hi,

Using kdenlive from svn and mlt from git (current as of yesterday) I am having problems with audio synchronization with .ogv files produced from recordmydesktop. The problem does not occur with the output of my Canon video camera (.MTS files containing x264 video and A52 audio).

When start playback or begin rendering from part way through one of these .ogv files it appears the audio starts too far back in the timeline, and then plays quickly for a while to catch up with the video.

After doing some of these arbitary start playbacks even playing from the beginning doesn't work correctly, with the video and audio being out of sync. I put a 15 second test clip (1.1mb in size) here:

http://www.saros.co.uk/misc/js/test.ogv

If you play this with mplayer first to get a correct rendering, you will see its just a static screen with audio. The audio is an introductory sentence and then some counting. Pull it into kdenlive time line and you can see the regular beats of the counting starting at 7 seconds. If I try to play just the counts I get the first half of the introduction babbled quickly, then the counting begins.

I created that ogv file using this:

recordmydesktop --width 1024 --height 720 --device default --overwrite --fps 25 -x 2 -y 1 -s_quality 10 --freq 48000 -o test.ogv

I would appreciate knowing if anyone else sees the same problem.

I have read this, but I am not using pulse audio, just alsa.
http://www.kdenlive.org/user-manual/troubleshooting-and-common-problems/sound-bad-and-delayed

And this one
http://www.kdenlive.org/forum/there-any-way-keep-audio-sync
My kernel is 2.6.29

An update on this.
The problem still occurs with the default options on recordmydesktop, eg

recordmydesktop --device default -o test3.ogv

Produces a file in which kdenlive struggles to locate the correct position in the audio channel.

However if I convert this to mp4 first using this command:

ffmpeg -i test3.ogv -f mp4 -vcodec libx264 -ab 256k -b 10000k -vpre normal -crf 22 -acodec libfaac test3.mp4

The resulting test3.mp4 works fine in kdenlive.

So I guess desktop recording is a two step process for now.

It would be good for convenience and presumably quality to get this fixed. I can help with testing easily since I am running out of git/svn anyway.

FFmpeg does not support seeking on Ogg Theora very well. It is a well known issue. I am working slowly on an alternative to FFmpeg libs for Ogg Theora, but it might take a little while. In the meantime, I have added 2 new Transcode presets (right-click clip in Project Tree) to Kdenlive to help with Ogg Theora. These presets will be in the next release, but you might have to delete an existing kdenlivetranscodingrc file to see them after upgrading. Anyways, now you can add these yourself in Kdenlive's Settings dialog:

Fix Ogg Theora = -sameq -vcodec libtheora -acodec copy %1.ogv

often that introduces an a/v sync problem. So, another new preset:

Lossless Matroska = -sn -vcodec huffyuv -acodec flac %1.mkv

works very well for me. It will create a much larger file, but you will not lose any quality and it is quite fast to work with.