Cutting a flv in Virtualdub - audio synch problems

[Faufiffon]

I have several flv videos taken from Justin TV that I want to cut with Virtualdub. I've opened the files in MediaInfo and it says the video codec is AVC (constant frame rate) and the audio codec mpeg layer 3 (constant bit rate). So I've installed the FLV plugin for Virtualdub by fccHandler + the x264vfw codec and the videos open fine in Virtualdub.

The problem is that when I cut parts of the videos (both audio and video set on direct stream copy), there is audio delay and audio drift in the resulting avi files. Also, when I load these resulting files in Virtualdub, I get the VBR audio pop-up/warning.

Before trying to fix these audio problems (I've tried already, still have problems with the audio drift), there is something I don't understand: how can a video with constant video frame rate and constant audio bit rate result in an avi with variable audio bit rate? I mean, I'm using direct stream copy for video and audio so it doesn't reencode anything right? Can anybody explain that to me?

[Baldrick]

I wouldn't use virtualdub for any flv with avc. I would try avidemux. Save a mp4.

[Faufiffon]

Thanks for your answer Baldrick. I've tried with avidemux, the audio is out of synch too on the output file (mp4). I haven't checked yet if there is audio delay AND audio drift like with Virtualdub but it's probably the same.

Back to the question in my first post: how can a file with CBR mp3 result in a file with VBR mp3 although there was no encoding when cutting the file (direct stream copy)? That's what I don't understand.

[edit: I've just checked the first file I've cut with Virtualdub in MediaInfo, it seems the mp3 audio is still CBR, BUT the video frame rate mode has been changed to variable. So the video seems to be the problem, not the audio. I still get the audio VBR pop-up when opening in Virtualdub though. I'm confused...]

[DB83]

AFAIK Direct Stream Copy is only intended for avi source files.

The higher the compression - and your source is likely to be highly compressed - the greater the chances of sync issues when editing