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I don't know what you mean by cross-frame data. The program is using ffmpeg's -ss, -t, and vcodec copy functionality, and I'm not sure how it handles these issues. I know that if you cut between keyframes (which is very likely to happen), then the data before the next keyframe will be lost, so it is not an exact cutting mechanism.

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That's another issue, but it can also lose other data which will cause warnings but play most likely with correct color reproduction.

I don't have such a source file handy to reproduce, but if you try enough ISO MP4 containers with H246, you will hit one where this is the case.

Is `-t` different from `-to` which I've been using?

libavcodec tries to recover from missing frames (you need this for TV broadcasts) but it's actually not very good at it for H.264. You'd almost always see major artifacts.

Any idea what the exact warning text is?

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