[FFmpeg-devel] [PATCH 2/2] avcodev/libdcadec: implement request_channel_layout

[wm4]

On Tue,  7 Jul 2015 03:06:24 -0300
James Almer <jamrial at gmail.com> wrote:

> Signed-off-by: James Almer <jamrial at gmail.com>
> ---
>  libavcodec/libdcadec.c | 34 ++++++++++++++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
> 
> diff --git a/libavcodec/libdcadec.c b/libavcodec/libdcadec.c
> index 4bc3765..796826e 100644
> --- a/libavcodec/libdcadec.c
> +++ b/libavcodec/libdcadec.c
> @@ -36,6 +36,8 @@ typedef struct DCADecContext {
>      int buffer_size;
>  } DCADecContext;
>  
> +static int downmix_warned = 0;
> +
>  static int dcadec_decode_frame(AVCodecContext *avctx, void *data,
>                                 int *got_frame_ptr, AVPacket *avpkt)
>  {
> @@ -131,6 +133,17 @@ static int dcadec_decode_frame(AVCodecContext *avctx, void *data,
>      if (exss = dcadec_context_get_exss_info(s->ctx)) {
>          enum AVMatrixEncoding matrix_encoding = AV_MATRIX_ENCODING_NONE;
>  
> +        if (!downmix_warned) {
> +            uint64_t layout = avctx->request_channel_layout;
> +
> +            if (((layout == AV_CH_LAYOUT_STEREO_DOWNMIX || layout == AV_CH_LAYOUT_STEREO) && !exss->embedded_stereo) ||
> +                ( layout == AV_CH_LAYOUT_5POINT1 && !exss->embedded_6ch))
> +                av_log(avctx, AV_LOG_WARNING, "%s downmix was requested but no custom coefficients are available, "
> +                                              "this may result in clipping\n",
> +                                              layout == AV_CH_LAYOUT_5POINT1 ? "5.1" : "stereo");
> +            downmix_warned = 1;
> +        }
> +

What does this mean? Does this happen with FFmpeg's DCA decoder too?

>          switch(exss->matrix_encoding) {
>          case DCADEC_MATRIX_ENCODING_SURROUND:
>              matrix_encoding = AV_MATRIX_ENCODING_DOLBY;
> @@ -195,6 +208,27 @@ static av_cold int dcadec_init(AVCodecContext *avctx)
>      if (avctx->flags & CODEC_FLAG_BITEXACT)
>          flags |= DCADEC_FLAG_CORE_BIT_EXACT;
>  
> +    if (avctx->request_channel_layout > 0 && avctx->request_channel_layout != AV_CH_LAYOUT_NATIVE) {
> +        switch (avctx->request_channel_layout) {
> +        case AV_CH_LAYOUT_STEREO:
> +        case AV_CH_LAYOUT_STEREO_DOWNMIX:
> +            /* libdcadec ignores the 2ch flag if used alone when no custom downmix coefficients
> +               are available, silently outputting a 5.1 downmix if possible instead.
> +               Using both the 2ch and 6ch flags together forces a 2ch downmix using default
> +               coefficients in such cases. This matches the behavior of the 6ch flag when used
> +               alone, where a 5.1 downmix is generated if possible, regardless of custom
> +               coefficients being available or not. */
> +            flags |= DCADEC_FLAG_KEEP_DMIX_2CH | DCADEC_FLAG_KEEP_DMIX_6CH;
> +            break;
> +        case AV_CH_LAYOUT_5POINT1:
> +            flags |= DCADEC_FLAG_KEEP_DMIX_6CH;
> +            break;
> +        default:
> +            av_log(avctx, AV_LOG_WARNING, "Invalid request_channel_layout\n");
> +            break;
> +        }
> +    }
> +
>      s->ctx = dcadec_context_create(flags);
>      if (!s->ctx)
>          return AVERROR(ENOMEM);