[FFmpeg-devel] [PATCH] Make a clear distinction between an unsupported codec and an unknown one

[Stefano Sabatini]

On date Sunday 2008-08-31 17:30:58 +0100, Robert Swain encoded:
> 2008/8/31 Vitor Sessak <vitor1001 at gmail.com>:
> > Robert Swain wrote:
> >> 2008/8/31 Peter Ross <pross at xvid.org>:
> >>> On Sun, Aug 31, 2008 at 12:53:34PM +0200, Michael Niedermayer wrote:
> >>>> On Sun, Aug 31, 2008 at 06:56:48AM +0200, Vitor Sessak wrote:
> >>>>> See $subj. I got pretty confused by "Stream #0.1: Audio: 0x0000, 5512 Hz,
> >>>>> mono, s16" meaning that a codec is known, but unsupported...
> >>>>>
> >>>>> -Vitor
> >>>>> Index: libavcodec/utils.c
> >>>>> ===================================================================
> >>>>> --- libavcodec/utils.c      (revision 15050)
> >>>>> +++ libavcodec/utils.c      (working copy)
> >>>>> @@ -1091,8 +1091,12 @@
> >>>>>                       (enc->codec_tag >> 16) & 0xff,
> >>>>>                       (enc->codec_tag >> 24) & 0xff,
> >>>>>                        enc->codec_tag);
> >>>>> +        } else if (enc->codec_id) {
> >>>>> +            snprintf(buf1, sizeof(buf1), "unsuported (id 0x%04x)", enc->codec_id);
> >>>>> +        } else if (enc->codec_tag) {
> >>>>> +            snprintf(buf1, sizeof(buf1), "unknown (0x%04x)", enc->codec_tag);
> >>>>>          } else {
> >>>>> -            snprintf(buf1, sizeof(buf1), "0x%04x", enc->codec_tag);
> >>>>> +            snprintf(buf1, sizeof(buf1), "unknown");
> >>>>>          }
> >>>> I think this is inconsistant now
> >>>> Before it just printed the tag now it prints the tag when its
> >>>> printable, if not and codec_id is not 0 the id and if not and
> >>>> id is 0 and the tag is not 0 the tag and ...
> >>>> Printing the ID in addition to the tag and "NONE" instead of
> >>>> 0x0000 or so seems more consistent to me
> >
> > IMHO, when we have a codec ID, the codec is already identified and there
> > is no use printing the 4CC. Yes, I should move them the "if
> > (enc->codec_id)" up.
> 
> Some people may be interested in the FOURCC even if they know the codec.
> 
> >>> An enhancement to the unsupported case would be to actually print
> >>> the name of the codec. e.g. i am always forgetting which 0x16X
> >>> twocc refers to wmav3.
> >>
> >> Indeed. In my opinion it should print the codec name if possible and
> >
> > Today we have:
> >
> > AVCodec flac_decoder = {
> >     "flac",
> >     CODEC_TYPE_AUDIO,
> >     CODEC_ID_FLAC,
> >     sizeof(FLACContext),
> >     flac_decode_init,
> >     NULL,
> >     flac_decode_close,
> >     flac_decode_frame,
> >     CODEC_CAP_DELAY,
> >     .flush= flac_flush,
> >     .long_name= NULL_IF_CONFIG_SMALL("FLAC (Free Lossless Audio Codec)"),
> > };
> >
> > AVCodec flac_encoder = {
> >     "flac",
> >     CODEC_TYPE_AUDIO,
> >     CODEC_ID_FLAC,
> >     sizeof(FlacEncodeContext),
> >     flac_encode_init,
> >     flac_encode_frame,
> >     flac_encode_close,
> >     NULL,
> >     .capabilities = CODEC_CAP_SMALL_LAST_FRAME,
> >     .sample_fmts = (enum SampleFormat[]){SAMPLE_FMT_S16,SAMPLE_FMT_NONE},
> >     .long_name = NULL_IF_CONFIG_SMALL("FLAC (Free Lossless Audio Codec)"),
> > };
> >
> > enum CodecID {
> >     CODEC_ID_NONE,
> >
> >     /* video codecs */
> >     CODEC_ID_MPEG1VIDEO,
> > [...]
> >
> >     CODEC_ID_FLAC,
> > [...]
> > }
> >
> > Note the duplication of both the short and the long name. I think that
> > setting the codec long and short name in the same place of CodecID would
> > remove duplication and resolve the issue of finding the name of
> > unimplemented codecs...
> 
> I like this idea. 

Just my 2 ?cent...

We could have a list of the format supported, with a name like
AVCodecFormat
or
AVStreamFormat

unfortunately the term "format" creates confusion with the specific
(and likely not-so-correct) use of term format done in libavformat.

Such structure could contain for example a name, long_name, fourcc,
type, and a list of encoders and decoders supporting it (yes it could
be more than one, think for example aac/libfaad, last time I tried to do:
ffmpeg -acodec libfaad -i ~/test.mov -ar 22100 -vcodec libx264 -t 1.0 -y outfile.mp4
I end up decoding with the native decoder...).

Also, maybe it would make sense to keep there the capabilities and the
list of supported things (pix_fmts, framerates, sizes etc.).

Then every codec could contain a list of the formats supported.

Regards.
-- 
FFmpeg = Free & Fiendish Magic Patchable Elastic Generator