[cm3]

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?

[astrange]

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?