[Libav-user] How to transcode mp3 file to G.711 encoded wav file

[Bob Kirnum]

Perhaps the AV_SAMPLE_FMT_S16 is referring to the sample format input to
the G.711 uLaw encoder (input should be 16 bit linear PCM)?  Then this
would be correct.  Perhaps split the effort and verify that you can decode
the MP3 to linear PCM properly, and encode linear to uLaw properly for WAV
separately?  Using the wrong sample rate (not downsampling to 8 kHz) would
not result in noise (what you reported), would just result in the wrong
audio speed.  One additional thought, does decoding the MP3 result in 16
bit integer linear PCM or 32 bit float PCM?  If float, that would be a
mismatch and result in noise when encoding to uLaw.

On Mon, Dec 6, 2021 at 10:40 AM Robert Smith via Libav-user <
libav-user at ffmpeg.org> wrote:

> If I change
>
> pCodecCtx->sample_fmt = AV_SAMPLE_FMT_S16;
>
> to
>
> pCodecCtx->sample_fmt = AV_SAMPLE_FMT_U8;
>
> Then I get the following error:
>
> [pcm_mulaw @ 0x2d33450] Specified sample_fmt is not supported.
>
> Any idea? Thanks
>
> On Friday, December 3, 2021, 06:15:54 PM EST, Bob Kirnum <
> bkirnum at gmail.com> wrote:
>
>
> G.711 is 8 bits, could be an issue. Also, not sure if you need to
> downsample to 8kHz manually or not.
>
> > On Dec 3, 2021, at 5:36 PM, Robert Smith via Libav-user <
> libav-user at ffmpeg.org> wrote:
> >
> > pCodecCtx->sample_fmt = AV_SAMPLE_FMT_S16;
>
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