[FFmpeg-devel] Make ffmpeg.c and ffplay.c use avctx->request_channels

[Michael Niedermayer]

On Wed, Dec 12, 2007 at 10:11:52AM +0100, Andreas ?man wrote:
> Hi
>
> Patch does $subj.
>
> I'm not sure if this change affects something that i'm not aware of.
> I've tested it with DTS and AC3 audio in various downmix scenarios.
> Regression tests passes as well.
>
> I assume this is the way forward (and what was meant by adding
> request_channels in the first place)
>

> Index: ffmpeg.c
> ===================================================================
> --- ffmpeg.c	(revision 11202)
> +++ ffmpeg.c	(working copy)
> @@ -1615,31 +1615,23 @@
>                  if (av_fifo_init(&ost->fifo, 2 * MAX_AUDIO_PACKET_SIZE))
>                      goto fail;
>  
> -                if (codec->channels == icodec->channels &&
> -                    codec->sample_rate == icodec->sample_rate) {
> -                    ost->audio_resample = 0;
> -                } else {
> -                    if (codec->channels != icodec->channels &&
> -                        (icodec->codec_id == CODEC_ID_AC3 ||
> -                         icodec->codec_id == CODEC_ID_DTS)) {
> -                        /* Special case for 5:1 AC3 and DTS input */
> -                        /* and mono or stereo output      */
> -                        /* Request specific number of channels */
> -                        icodec->channels = codec->channels;
> -                        if (codec->sample_rate == icodec->sample_rate)
> -                            ost->audio_resample = 0;
> -                        else {
> -                            ost->audio_resample = 1;
> -                        }
> -                    } else {
> -                        ost->audio_resample = 1;
> -                    }
> -                }
> +                if (codec->sample_rate != icodec->sample_rate)
> +                    ost->audio_resample = 1;
> +
> +                j = icodec->channels;
> +
> +                if (icodec->channels > 2 && codec->channels < icodec->channels)
> +                    /* Ask codec to do multichannel downmix for us */
> +                    j = icodec->request_channels = codec->channels;
> +                else if (codec->channels != icodec->channels)
> +                    /* Let audio_resample() try to mix channels */
> +                    ost->audio_resample = 1;
> +
>                  if(audio_sync_method>1)
>                      ost->audio_resample = 1;
>  
>                  if(ost->audio_resample){
> -                    ost->resample = audio_resample_init(codec->channels, icodec->channels,
> +                    ost->resample = audio_resample_init(codec->channels, j,
>                                                      codec->sample_rate, icodec->sample_rate);

you assume that every codec with >2 chans can downmix this is likely not the
case
a CODEC_CAP_DOWNMIX could be added or just check the channels number after
avcodec_open()

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

When you are offended at any man's fault, turn to yourself and study your
own failings. Then you will forget your anger. -- Epictetus
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