[FFmpeg-devel] [PATCH] avcodec/atrac3plus: reorder channels to match the output layout

[Andreas Rheinhardt]

James Almer:
> The order in which the channels are coded in the bitstream do not always follow
> the native, bitmask-based order of channels both signaled by the WAV container
> and forced by this same decoder. This is the case with layouts containing an
> LFE channel, as it's always coded last.
> 
> Fixes ticket #9964.
> 
> Signed-off-by: James Almer <jamrial at gmail.com>
> ---
> 6.1 and 7.1 untested, but much like 5.1 they were wrong before this change.
> 
>  libavcodec/atrac3plusdec.c | 25 ++++++++++++++++++++++---
>  1 file changed, 22 insertions(+), 3 deletions(-)
> 
> diff --git a/libavcodec/atrac3plusdec.c b/libavcodec/atrac3plusdec.c
> index ee71645a3c..8c3d20af76 100644
> --- a/libavcodec/atrac3plusdec.c
> +++ b/libavcodec/atrac3plusdec.c
> @@ -65,6 +65,7 @@ typedef struct ATRAC3PContext {
>  
>      int num_channel_blocks;     ///< number of channel blocks
>      uint8_t channel_blocks[5];  ///< channel configuration descriptor
> +    AVChannelLayout coded_ch_layout; ///< order of channels as coded in the bitstream
>  } ATRAC3PContext;
>  
>  static av_cold int atrac3p_decode_close(AVCodecContext *avctx)
> @@ -74,6 +75,8 @@ static av_cold int atrac3p_decode_close(AVCodecContext *avctx)
>      av_freep(&ctx->ch_units);
>      av_freep(&ctx->fdsp);
>  
> +    av_channel_layout_uninit(&ctx->coded_ch_layout);
> +
>      ff_mdct_end(&ctx->mdct_ctx);
>      ff_mdct_end(&ctx->ipqf_dct_ctx);
>  
> @@ -84,6 +87,7 @@ static av_cold int set_channel_params(ATRAC3PContext *ctx,
>                                        AVCodecContext *avctx)
>  {
>      int channels = avctx->ch_layout.nb_channels;
> +    int ret;
>      memset(ctx->channel_blocks, 0, sizeof(ctx->channel_blocks));
>  
>      av_channel_layout_uninit(&avctx->ch_layout);
> @@ -92,17 +96,20 @@ static av_cold int set_channel_params(ATRAC3PContext *ctx,
>          avctx->ch_layout        = (AVChannelLayout)AV_CHANNEL_LAYOUT_MONO;
>          ctx->num_channel_blocks = 1;
>          ctx->channel_blocks[0]  = CH_UNIT_MONO;
> +        ctx->coded_ch_layout    = avctx->ch_layout;
>          break;
>      case 2:
>          avctx->ch_layout        = (AVChannelLayout)AV_CHANNEL_LAYOUT_STEREO;
>          ctx->num_channel_blocks = 1;
>          ctx->channel_blocks[0]  = CH_UNIT_STEREO;
> +        ctx->coded_ch_layout    = avctx->ch_layout;
>          break;
>      case 3:
>          avctx->ch_layout        = (AVChannelLayout)AV_CHANNEL_LAYOUT_SURROUND;
>          ctx->num_channel_blocks = 2;
>          ctx->channel_blocks[0]  = CH_UNIT_STEREO;
>          ctx->channel_blocks[1]  = CH_UNIT_MONO;
> +        ctx->coded_ch_layout    = avctx->ch_layout;
>          break;
>      case 4:
>          avctx->ch_layout        = (AVChannelLayout)AV_CHANNEL_LAYOUT_4POINT0;
> @@ -110,6 +117,7 @@ static av_cold int set_channel_params(ATRAC3PContext *ctx,
>          ctx->channel_blocks[0]  = CH_UNIT_STEREO;
>          ctx->channel_blocks[1]  = CH_UNIT_MONO;
>          ctx->channel_blocks[2]  = CH_UNIT_MONO;
> +        ctx->coded_ch_layout    = avctx->ch_layout;
>          break;
>      case 6:
>          avctx->ch_layout        = (AVChannelLayout)AV_CHANNEL_LAYOUT_5POINT1_BACK;
> @@ -118,6 +126,9 @@ static av_cold int set_channel_params(ATRAC3PContext *ctx,
>          ctx->channel_blocks[1]  = CH_UNIT_MONO;
>          ctx->channel_blocks[2]  = CH_UNIT_STEREO;
>          ctx->channel_blocks[3]  = CH_UNIT_MONO;
> +        ret = av_channel_layout_from_string(&ctx->coded_ch_layout, "FL+FR+FC+BL+BR+LFE");
> +        if (ret < 0)
> +            return ret;
>          break;
>      case 7:
>          avctx->ch_layout        = (AVChannelLayout)AV_CHANNEL_LAYOUT_6POINT1_BACK;
> @@ -127,6 +138,9 @@ static av_cold int set_channel_params(ATRAC3PContext *ctx,
>          ctx->channel_blocks[2]  = CH_UNIT_STEREO;
>          ctx->channel_blocks[3]  = CH_UNIT_MONO;
>          ctx->channel_blocks[4]  = CH_UNIT_MONO;
> +        ret = av_channel_layout_from_string(&ctx->coded_ch_layout, "FL+FR+FC+BL+BR+BC+LFE");
> +        if (ret < 0)
> +            return ret;
>          break;
>      case 8:
>          avctx->ch_layout        = (AVChannelLayout)AV_CHANNEL_LAYOUT_7POINT1;
> @@ -136,6 +150,9 @@ static av_cold int set_channel_params(ATRAC3PContext *ctx,
>          ctx->channel_blocks[2]  = CH_UNIT_STEREO;
>          ctx->channel_blocks[3]  = CH_UNIT_STEREO;
>          ctx->channel_blocks[4]  = CH_UNIT_MONO;
> +        ret = av_channel_layout_from_string(&ctx->coded_ch_layout, "FL+FR+FC+BL+BR+SL+SR+LFE");
> +        if (ret < 0)
> +            return ret;
>          break;
>      default:
>          av_log(avctx, AV_LOG_ERROR,
> @@ -377,10 +394,12 @@ static int atrac3p_decode_frame(AVCodecContext *avctx, AVFrame *frame,
>          reconstruct_frame(ctx, &ctx->ch_units[ch_block],
>                            channels_to_process, avctx);
>  
> -        for (i = 0; i < channels_to_process; i++)
> -            memcpy(samples_p[out_ch_index + i], ctx->outp_buf[i],
> +        for (i = 0; i < channels_to_process; i++) {
> +            enum AVChannel ch = av_channel_layout_channel_from_index(&ctx->coded_ch_layout, out_ch_index + i);
> +            int idx = av_channel_layout_index_from_channel(&frame->ch_layout, ch);
> +            memcpy(samples_p[idx], ctx->outp_buf[i],
>                     ATRAC3P_FRAME_SAMPLES * sizeof(**samples_p));
> -
> +        }
>          ch_block++;
>          out_ch_index += channels_to_process;
>      }

Wouldn't it be simpler to just use a hardcoded array like { 0, 1, 2, 4,
5, 6, 3 } for 6.1 (and other arrays for the other layouts) instead of
using the channel layout API to do it (after all, the order of channels
in enum AVChannel won't change)? This would avoid the allocations
inherent in av_channel_layout_from_string() as well as the function
calls in atrac3p_decode_frame().

Apart from that, setting a channel layout via assignment is forbidden
(yes, i know it is safe here, because you are just copying an explicit
layout once more).

- Andreas