On 03/07/2024 11:56, Bernardo Pilarz via ffmpeg-devel wrote:
On 03/07/2024 11:10, Anton Khirnov wrote:
Quoting Bernardo Pilarz via ffmpeg-devel (2024-07-03 10:10:15)
+ char *codec_name;
const struct AVCodec *codec;
enum AVCodecID codec_id; /* see AV_CODEC_ID_xxx */
Adding a new field here is an ABI break, it would need to go at the
end of the struct.
In general, I feel like this might be better served to go into
metadata though, especially as very few containers have a string codec
identifier to begin with.
I would be very glad to do it the right way, but I need some guidance
since this is the first time I try to contribute to FFmpeg.
The problem that I am trying to solve is receiving metadata from an
RTSP
stream (in example, ONVIF metadata identified by the codec name
'vcd.onvif.metadata').
This is data that the application will want to handle on its own (and
not through FFmpeg).
Can you guide me on how to do this properly?
First of all, this should definitely NOT go into AVCodecContext, since
the entire premise is that we have no codec ID and hence no decoders or
encoders, so a codec context makes no sense.
Next, the idea that you can define a generic container-independent
"codec name" sounds dubious to me, as they are not universally
standardized. You'd either have to define precisely what can the API
caller expect in there, or make this a private AV_OPT_FLAG_EXPORT option
of your demuxer. I'd suggest the second, as it's much simpler, though
IIRC we do not yet support per-stream private options.
I ended up adding it to the AVCodecContext because
'avformat_find_stream_info()' invokes
'avcodec_parameters_to_context()' followed by
'avcodec_parameters_from_context()', thereby overwriting the entire
'codecpar' field of each stream in my format context.
This also means that an AVCodecContext is in fact created even for
streams with no codec ID.
It's not clear to me how I can use AV_OPT_FLAG_EXPORT (it's my fault
because I don't know the library so well).
It might very well be the solution I am looking for, but I need some
help in understanding how to implement it.
The basic problem is I need to get the "codec name" information that
is available in 'sdp_parse_rtpmap()' and is completely lost when the
codec is not supported by FFmpeg.
By the way, we are talking of AVMEDIA_TYPE_DATA streams, and codecs
that are potentially custom/not widespread and therefore should
probably be handled by the application rather than by ffmpeg itself.
P.S.: I am currently only using FFmpeg to grab an RTSP stream. The
audio and video streams might very well get decoded using FFmpeg later
on, but so far I am only concerned with getting the compressed packets
and being able to read their declared codec names.
How about putting this information in the stream's
'codecpar.coded_side_data'?
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