No video in virtualdub after cut and split avi

[cooljoe666]

I have taken a Divx video in the latest virtualdub and cut and saved it in parts via direct stream. Then I attempted to convert each part to a newly formatted file using the same program. Problem is that only the first one converted properly, I think because it was cut out at the very beginning of the big file (headers?). The rest show up blank when reloaded into vdub. They stay black when converted. If I load them into Tmpgenc Xpress they show up green. Still, I can play them all in any media player and they are perfect.

Why can I not convert these files?

I'll create some more confusion. I am running WIndows 7 64-bit. I have both Virtualdub 32-bit and 64-bit versions. I can open the cut up files in the 64-bit vdub and they play back and convert easily. But it is the 32-bit vdub that only shows black (with audio). I need to use the 32-bit vdub because of the vfw codec being used.

Any ideas?

[Mini-Me]

Unless you're carefully cutting at GOP (group of pictures) boundaries, my best guess is that your problem has to do with inter-frame compression. MPEG-4 ASP (Divx) uses groups of frames, where most frames within the group reference other ones. Wikipedia has a pretty decent page explaining the different types of frames. If you cut such a file in the middle of one of these groups, especially using direct stream copy, then your new files will try to reference frames that don't exist in the trimmed stream. This is why MPEG-2, MPEG-4 ASP (Divx, Xvid, etc.), and H.264 video formats are considered somewhat difficult to edit. (Actually, some formats even allow "open" GOP's, which allow frames to reference frames from other groups entirely. This further increases compression efficiency at the expense of seeking and editing.)

Depending on what decoding libraries are used, dedicated media players may just be better than other programs at piecing together what's left of the partial stream (or throwing out a few frames so the rest can be played back), which could explain why you get different results playing back from different programs.

[naszdom]

I have just encountered this although I have been splitting files for years. I have found that the first part is alright but the second part will not play on anything but VLC. Since most stand alones do not like files of more than 1gb is there any easy way round it except to convert the whole file back to mpg?

[hech54]

Basically it boils down to "cutting on key frames" so to speak. You can't just cut anywhere with Xvid/Divx.

[jagabo]

VirtualDub in "direct stream copy" mode will only cut on key frames. If you mark-in on a non key frame it will automatically move the cut (when it saves that clip to a file) to the key frame immediately before the cut. There's no indication of this in the UI.

[naszdom]

Both cooljoe666 and I have used VirtualDub. If VirtualDub only cuts on key frames then why in my case does only the first part play? The same thing happens with Avidemux

Whatever the problem is its beyond VirtualDub. Getting back to what Mini-Me said I would like to know how to else to cut rather than re-encode.

[jagabo]

VirtualDub and AviDemux are the only programs I've used for non-reencoding cuts of AVI files. I believe ffmpeg has the ability too.

[lowellriggsiam]

Maybe the second half looses it's index...try running one of them through divfix and see if that repairs it.

[jagabo]

Maybe the second half looses it's index...

Yes, but why should the index be lost? VirtualDub and AviDemux know how to handle the index.

[lowellriggsiam]

I have seen various odd things happen when video are split. I suspect the first part keeps the original index and the remaining half is erronenously given a false one possibly caused by a glitch in the video stream, or a problem caused by a variable bitrate. In the cases where these problems occur I suspect there is message pops up just after loading the file.

[naszdom]

I did not try divfix but I did try avifixed - no joy.
VirtualDub showed no warning at all.

If anyone knows what it means Gspot refers to

Note: 36 bytes unneeded bytes at end of file
AVI v1.0
Interleave: 43 ms (1.1 v.frames)
Audio frames: Aligned on interleaves

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