[FFmpeg-devel] [RFC] Documenting metadata keys, informative (non-copied) metadata

[Marvin S.]

On 18 Feb 2025, at 17:56, Tomas Härdin wrote:

> tor 2025-02-13 klockan 12:54 +0100 skrev Tomas Härdin:
>> Hi
>>
>> In the samples_md5 patch discussion Michael wanted the proposed key
>> to
>> be documented. But it turns out we don't have any documentation for
>> metadata keys! So I'm starting this thread to talk about it. I reckon
>> we create a new file called doc/metadata_keys.texi with a table
>> listing
>> keys and where they can appear (format, stream, frames), sorted by
>> name, with a brief description of each one. Any keys that require
>> more
>> detailed documentation we could add sections for.
>>
>> Another issue raised was that some metadata keys shouldn't be carried
>> over automatically to muxers. In the samples_md5 thread it was
>> pointed
>> out by Andreas that we don't want to mux that in AIFF. It was also
>> pointed out that it stops being valid if the audio is cut. This isn't
>> the first time I've come across cases where we don't want metadata to
>> be copied, so I'm taking the opportunity to propose informative
>> output-
>> only metadata could reside in their own namespace. I propose info:
>> for
>> that, so info:samples_md5 in this specific case, or maybe just
>> info:md5. HEVC frames could similarly have such metadata applied.

In reference to the AVDictionary patches (it was an attachment so I can
not comment inline):

IMHO such handling doesn't belong in an abstract container class.

It is surprising behaviour that a dictionary cares about
how the keys look (beyond the case-sensitive handling).

I am not saying this isn't useful but I do not think it belongs in
AVDictionary directly.

>
> Attached is a PoC for the latter part. Unlike the previous samples_md5
> patch, this one only requires updating a FATE ref concerning a .flac
> file.
>
> I have to go, else I'd also post the documentation thing as well.
>
> /Tomas
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