[FFmpeg-devel] [RFC] stream parsing

[Michael Niedermayer]

On Sun, Sep 26, 2010 at 12:54:34PM +0200, Benjamin Larsson wrote:
> 
> > 
> > this looks strange
> > i would have expected a
> > if((codec->capabilities & CODEC_CAP_CHANNEL_CONF) && !channel_layout)
> >     return 0;
> > 
> > in has_codec_parameters()
> 
> 
> There is no AVCodec available in has_codec_parameters() only an
> AVCodecContext.
> 
> > 
> > but maybe this doesnt work for some case?
> 
> It wont work as it's the wrong struct.
> 
> 
> > 
> > at least your "if we dont have all parameters remove these 3 parameters"
> > is looking worse
> > 
> 
> This is what the AAC codec uses, I'm not saying its correct I just took
> something that worked. But IIRC something need to set these to 0 before
> opening the decoder otherwise it will use the values the demuxer set.
> 
> Anyway I redid the patch, it's abit more logical now but pretty much the
> same.
> 
> Btw in has_codec_parameters() there is a list of codecs with some
> special casing, I think these codecs should have this new capability set.
> 
> MvH
> Benjamin Larsson

>  libavcodec/avcodec.h |    5 +++++
>  libavcodec/dca.c     |    1 +
>  libavformat/utils.c  |   27 ++++++++++++++++++++-------
>  3 files changed, 26 insertions(+), 7 deletions(-)
> ab6630288f93c954106ef242caf7ab19da255387  codec_cap_channel_conf.diff
> Index: libavcodec/avcodec.h
> ===================================================================
> --- libavcodec/avcodec.h	(revision 25194)
> +++ libavcodec/avcodec.h	(working copy)
> @@ -684,7 +684,12 @@
>   * encoders
>   */
>  #define CODEC_CAP_EXPERIMENTAL     0x0200
> +/**
> + * Codec should fill in channel configuration and samplerate instead of container
> + */
> +#define CODEC_CAP_CHANNEL_CONF     0x0400
>  
> +
>  //The following defines may change, don't expect compatibility if you use them.
>  #define MB_TYPE_INTRA4x4   0x0001
>  #define MB_TYPE_INTRA16x16 0x0002 //FIXME H.264-specific
> Index: libavcodec/dca.c
> ===================================================================
> --- libavcodec/dca.c	(revision 25194)
> +++ libavcodec/dca.c	(working copy)
> @@ -1500,4 +1500,5 @@
>      .decode = dca_decode_frame,
>      .close = dca_decode_end,
>      .long_name = NULL_IF_CONFIG_SMALL("DCA (DTS Coherent Acoustics)"),
> +    .capabilities = CODEC_CAP_CHANNEL_CONF,
>  };
> Index: libavformat/utils.c
> ===================================================================
> --- libavformat/utils.c	(revision 25194)
> +++ libavformat/utils.c	(working copy)
> @@ -1995,12 +1995,22 @@
>  #endif
>  }
>  
> -static int has_codec_parameters(AVCodecContext *enc)
> +static int has_codec_parameters(AVCodecContext *enc, AVCodec *codec)
>  {
>      int val;
>      switch(enc->codec_type) {
>      case AVMEDIA_TYPE_AUDIO:
>          val = enc->sample_rate && enc->channels && enc->sample_fmt != SAMPLE_FMT_NONE;
> +        /* Some containers report wrong information about channel configuration
> +         * let the codecs handle it in those cases (dca for example)).
> +         */
> +        if (codec && codec->capabilities & CODEC_CAP_CHANNEL_CONF) {
> +            enc->sample_rate    = 0;
> +            enc->channel_layout = 0;
> +            enc->frame_size     = 0;
> +            enc->channels       = 0;
> +            return 0;
> +        }

av_find_stream_info() will return once all streams has_codec_parameters()
return non zero
this explicitly returns 0 unconditional on any parameters being available or
not thus has_codec_parameters() will never return non zero for an affected
stream, leading to exit only by bug and time/pos limits

like i said the code should test if channel_layout has been set and
return 0 if not it should not set any variable to 0 because this is unneeded
that is unless it is actually needed but then id like to know why

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Everything should be made as simple as possible, but not simpler.
-- Albert Einstein
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