[FFmpeg-user] Per frame metadata example?

Paul B Mahol onemda at gmail.com
Sun Jul 14 00:53:49 EEST 2019

On 7/13/19, Francesco Pretto <ceztko at gmail.com> wrote:
> On Sat, 13 Jul 2019 at 22:33, Paul B Mahol <onemda at gmail.com> wrote:
>> NUT does not support that.
>> What convinced you it does support it?
> The NUT specification[1] talks specifically about per-frame metadata
> support:

That is very vague and unspecific wording to claim such feature.
And specification is misleading you.
Anyway NUT specification was written much before introduction
of frame metadata as we know it.

So what you actually pointed out have nothing to do with frame metadata, but
with updating stream metadata within new packet side data.

> ----------------------------------------------
> sm_data / side_data / meta_data
>     This data structure is used both in frames for per frame side and
> metadata
>     as well as info tags for metadata covering the whole file, a stream
>     chapter or other.
> [...]
>     Types of per frame side data:
> [...]
>     "UserData<identifer here>"
>         User specific side data, the "<identifer here>" should be replaced
>         by a globally unique identifer of the project that
>         uses/creates/understands the side data. For example "UserDataFFmpeg"
> ----------------------------------------------
> The nut encoder[2] and decoder[3] code seems to fully handle this data
> already
> at AVPacket level, so either this metadata was (improperly?) named per-frame
> when it's actually per-packet, and some glue code is missing that mux and
> demux
> the metadata between frames <-> packet, or there's a bug somewhere.
> Also this feature request[4] asks for per-frame metadata in Matroska
> similarly to what it was done in NUT. This was all the evidence I could find
> but no full example.
> Cheers,
> Francesco
> [1] http://ffmpeg.org/~michael/nut.txt
> [2] https://github.com/FFmpeg/FFmpeg/blob/master/libavformat/nutenc.c
> , write_sm_data()
> [3] https://github.com/FFmpeg/FFmpeg/blob/master/libavformat/nutdec.c
> , read_sm_data()
> [4] https://github.com/cellar-wg/matroska-specification/issues/270
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