[FFmpeg-trac] #4706(documentation:open): av_guess_codec ignores short_name, filename, and mime_type

[FFmpeg]

#4706: av_guess_codec ignores short_name, filename, and mime_type
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             Reporter:  andrewrk     |                    Owner:
                 Type:  defect       |                   Status:  open
             Priority:  minor        |                Component:
              Version:  git-master   |  documentation
             Keywords:               |               Resolution:
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0
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Comment (by andrewrk):

 > My original interpretation of this ticket was that you argued that the
 short_name
 > parameter of av_guess_codec() should have precedence over the fmt
 parameter. Was I
 > correct?

 No. The title of the ticket is correct as well as my clarified code
 example.

 I do not think the short_name of the codec should change what *format* is
 used, but I do think the short_name of the codec should change what
 *codec* is used.

 > Why are you calling av_guess_codec() if you know exactly what codec you
 want to use?

 The ingredients for choosing a format and codec are:

  * format: format short name, filename hint, codec mime type
  * codec: the format, codec short name, filename hint, codec mime type

 So it seems that the API user should be able to call av_guess_format,
 supply the format choosing ingredients, get a format. Then call
 av_guess_codec, supply the codec choosing ingredients, get a codec.

 But it is not this way. Here's how my code looks currently:


 {{{
     e->oformat = av_guess_format(encoder->format_short_name,
             encoder->filename, encoder->mime_type);
     if (!e->oformat) {
         groove_encoder_detach(encoder);
         av_log(NULL, AV_LOG_ERROR, "unable to determine format\n");
         return -1;
     }

     // av_guess_codec ignores mime_type, filename, and codec_short_name.
 see
     // https://trac.ffmpeg.org/ticket/4706
     // because of this we do a workaround to return the correct codec
 based on
     // the codec_short_name.
     AVCodec *codec = NULL;
     if (encoder->codec_short_name) {
         codec = avcodec_find_encoder_by_name(encoder->codec_short_name);
         if (!codec) {
             const AVCodecDescriptor *desc =
                 avcodec_descriptor_get_by_name(encoder->codec_short_name);
             if (desc) {
                 codec = avcodec_find_encoder(desc->id);
             }
         }
     }
     if (!codec) {
         enum AVCodecID codec_id = av_guess_codec(e->oformat,
                 encoder->codec_short_name, encoder->filename,
 encoder->mime_type,
                 AVMEDIA_TYPE_AUDIO);
         codec = avcodec_find_encoder(codec_id);
         if (!codec) {
             groove_encoder_detach(encoder);
             av_log(NULL, AV_LOG_ERROR, "unable to find encoder\n");
             return -1;
         }
     }
     e->codec = codec;
     av_log(NULL, AV_LOG_INFO, "encoder: using codec: %s\n",
 codec->long_name);

 }}}

--
Ticket URL: <https://trac.ffmpeg.org/ticket/4706#comment:4>
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