stsd: add roundtrip support for unknown codec

[paroga]

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Reviewing files that changed from the base of the PR and between 8f1ef32 and 1b74ecf.

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• src/error.rs
• src/moov/trak/mdia/minf/stbl/stsd/mod.rs

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[bradh]

Again, what is the intent? If we don't understand the codec, you can't make meaningful changes, so why read or write it...

[paroga]

what is the intent?

merging a fragmented mp4.

as long as the codec has no strange behavior it should be possible to merge samples from multiple moof+mdat into a single moov+mdat without understanding the full details of stsd

[bradh]

what is the intent?

merging a fragmented mp4.

For what purpose?

as long as the codec has no strange behavior it should be possible to merge samples from multiple moof+mdat into a single moov+mdat without understanding the full details of stsd

There are a bunch of strange behaviours in the codecs we don't support, like layer enhancements, scaling, image sequences etc. I think this behaviour is dangerous. I might be able to live with it behind a feature flag, but would prefer to see the specific codecs implemented if you need them.

[paroga]

merging a fragmented mp4.

For what purpose?

allow playback in players which don't support fragmented files (check out windows)

but if you don't like that point, take an even more simple use case: parse a MP4 file, add/edit some meta atoms and write it again. in that case the actual codec should not matter

There are a bunch of strange behaviours in the codecs we don't support, like layer enhancements, scaling, image sequences etc. I think this behaviour is dangerous. I might be able to live with it behind a feature flag, but would prefer to see the specific codecs implemented if you need them.

i'd more prefer some kind of runtime flag. using feature flags in bigger project can lead to problems if they change behavior. some other crate in a workspace can enable a feature and then it's enabled for all crates (see also #105)