Problem Viewing MP-4 In VirtualDub

[Avagadro1]

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[davexnet]

Some kind of decoding error ...

[poisondeathray]

Do the "broken" ones play in a media player without issues (e.g. vlc, mpchc, mpv... ) ?

If they play ok, it might just be an old decoder. The ffmpeg input driver for vdub classic is a few years old

Try vdub2; it contains everything you need to decode without external plugins , including newer formats like av1, hevc . ffmpeg input driver does not.

If they are "broken" in everything, then they are probably... broken

[Avagadro1]

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[davexnet]

Virtualdub2 is still being developed, the author occasionally appears in this forum to take bug reports and questions.
The original Virtualdub hasn't been touched in many years.

Use vdub2; if you have a specific issue with it, bring it to the forum here

[jagabo]

That is a common decoding error with long GOP, out-of-order, interframe codecs and some source filters. As you found, using a different source filter (implied by using a different program) can take care of the problem.