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View Full Version : DV Audio disappears after 15 minutes in Vdub/Avisynth but not Media Player?


Metaluna
5th November 2003, 09:22
I've started seeing a strange problem in my Canopus ADVC-100 captures.

I have a library of 6-hour EP-mode tapes of a TV show that I've been archiving to DVD. My normal workflow is to capture the entire tape in one pass into a giant Type 2 AVI file using Scenalyzer Live, then cut commercials and split the tape into individual episodes using AVIsynth, frameserved to TMPGEnc for encoding. I always ensure that I have zero dropped frames before proceeding.

The problem I've been seeing is that, on some captures, the audio seems to disappear into dead silence at a certain point about 15-17 minutes into the capture, never to return for the remaining 5+ hours of the capture. This only happens if I open the avi file in Avisynth or VirtualDub. If I open the file in Windows Media Player 9, the audio is fine (though there may be a small glitch right at the frame where the audio drops...I'm not sure if this is relevant or is something that was present in the source).

The dropout point is very consistent and never moves around. For example if the dropout happens at 17 minutes and 30 seconds into the capture, and I use AVIsynth's Trim() and aligned splice commands to cut 3 minutes out of the video, the dropout will move to 14:30. I have tried different DV codecs (Panasonic and Mainconcept), and even playing the file back on different PC's, and the results are always the same, with the audio dropping at the same point in the file.

Does anyone have a clue as to what might be happening? Could this be some kind of VfW vs. DirectShow thing? I suppose there could be something wrong with the ADVC-100, but that still doesn't explain why it plays fine in Media Player.

bb
5th November 2003, 18:23
I assume there's an error in the stream, and errors may be handled differently in VfW vs. DirectShow, not to mention that the decoders used are completely different. What happens if you cut out a few seconds (or even just two frames or so) around the frame where the audio stops, I mean if you cut out the error?

bb

Metaluna
6th November 2003, 01:27
That seems to have no effect, even if I chop a hundred frames off of either side of the approximate error point. In fact I can set up Avisynth to jump into the stream hundreds of thousands of frames after the error point (so it would never pass through that section of the stream) and the audio is still gone.

If I open the file in avisynth using DirectShowSource instead of AviSource, it seems to keep the audio, except that now it falls out of sync (it's about 1/3 sec early) sometime after the error point. I'm experimenting right now with using Type 1 AVI's in combination with the new release candidate of AVIsynth that allows navigation with DirectShowSource (so cutting and joining is possible).