[FFmpeg-devel] possible bug in pcm.c

[Paul B Mahol]

On 10/20/13, Lukasz M <lukasz.m.luki at gmail.com> wrote:
> Hi,
>
> I work on code that reads stream from input, decodes audio
> with avcodec_decode_audio4 and then encode frame again.
> Output muxer is pulse device. I use AV_CODEC_ID_PCM_S16LE codec (taken from
> device) and AV_SAMPLE_FMT_S16 sample format
>
> Input has 2 channels. I got a noise on speakers. I was strugging a lot and
> finally debugged it:
>
> after decoding with avcodec_decode_audio4, frame has sample
> format AV_SAMPLE_FMT_S16P, 2 channels.
> During encoding frame->data[0] is taken as a source for all samples, but it
> has data only for one channel, second one is on frame->data[1]

I'm little confused what exactly your code does?

>
> static int pcm_encode_frame(...)
> [...]
>     sample_size = av_get_bits_per_sample(avctx->codec->id) / 8;
>     n           = frame->nb_samples * avctx->channels;
>     samples     = (const short *)frame->data[0];
>
> [...]
>
> switch (avctx->codec->id) {
> [...]
>     case AV_CODEC_ID_PCM_S16LE:
> #endif /* HAVE_BIGENDIAN */
>     case AV_CODEC_ID_PCM_U8:
>         memcpy(dst, samples, n * sample_size);
>         break;
>
> It seems pcm_encode_frame doesn't support AV_SAMPLE_FMT_S16P frames
> correctly.
>
> I made a test and set output codec to 1 channel and it works correctly
> (clean sound on speakers)
>
> Can someone confirm it is a bug?

pcm.c code is correct.

>
> Best regards,
> Lukasz Marek
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