[FFmpeg-devel] [PATCH] doc/examples/decode_audio: read the audio data from data[0]

[Hendrik Leppkes]

On Tue, Oct 8, 2019 at 10:44 AM Steven Liu <lq at chinaffmpeg.org> wrote:
>
> only frame linesize[0] can get length size,
> i have tested before patch like this:
> ffmpeg -i /Users/liuqi/input.mp3 -codec:a ac3 -ac 5 a.ac3
> ./doc/examples/decode_audio a.ac3 a.pcm
> ffplay -f f32le -ac 5 -ar 44100 a.pcm
> there have problem.
>
> no problem after this patch.
>
> Reported-by: Bepartofyou
> Signed-off-by: Steven Liu <lq at chinaffmpeg.org>
> ---
>  doc/examples/decode_audio.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/doc/examples/decode_audio.c b/doc/examples/decode_audio.c
> index 6c2a8ed550..4a81302ad3 100644
> --- a/doc/examples/decode_audio.c
> +++ b/doc/examples/decode_audio.c
> @@ -98,7 +98,7 @@ static void decode(AVCodecContext *dec_ctx, AVPacket *pkt, AVFrame *frame,
>          }
>          for (i = 0; i < frame->nb_samples; i++)
>              for (ch = 0; ch < dec_ctx->channels; ch++)
> -                fwrite(frame->data[ch] + data_size*i, 1, data_size, outfile);
> +                fwrite(frame->data[0] + data_size*i, 1, data_size, outfile);
>      }
>  }
>

This change is definitely not correct. Without further changes, all
this does is copy the same block up to "channels" times. But whats
with all the other channel?

The current code is correct for handling planar audio. (ie. S16P/FLTP,
for example), but not packed audio (ie. S16/FLT). If you want to
support both planar and packed, you will need more changes then this.

- Hendrik