[FFmpeg-devel] [RFC] av_get_bits_per_sample() questions

[Alex Converse]

On Sun, Mar 13, 2011 at 2:20 PM, Justin Ruggles
<justin.ruggles at gmail.com> wrote:
> On 03/13/2011 04:59 PM, Stefano Sabatini wrote:
>
>> Hi,
>>
>> just discovered that we have:
>>
>> int av_get_bits_per_sample(enum CodecID codec_id);
>> and:
>> int av_get_bits_per_sample_fmt(enum AVSampleFormat sample_fmt);
>>
>> av_get_bits_per_sample() return per-codec bits per sample, and is only
>> used in pcm:
>> ./pcm.c:48: ? ?avctx->bits_per_coded_sample = av_get_bits_per_sample(avctx->codec->id);
>> ./pcm.c:93: ? ?sample_size = av_get_bits_per_sample(avctx->codec->id)/8;
>> ./pcm.c:232: ? ? ? ?avctx->bits_per_raw_sample = av_get_bits_per_sample(avctx->codec->id);
>> ./pcm.c:285: ? ?sample_size = av_get_bits_per_sample(avctx->codec_id)/8;
>> ./pcm.c:287: ? ?/* av_get_bits_per_sample returns 0 for CODEC_ID_PCM_DVD */
>>
>> Since this is a per-codec property I wonder if it would be a better
>> idea to put the information in the codec context and drop the
>> function.
>
> I agree it's ugly.
>
> I think it's supposed to just be a convenience function for libavformat
> and other muxers/demuxers to be able to handle raw pcm/adpcm/dpcm more
> easily. ?I think it would be ok to redefine how bits_per_raw_sample is
> used as an alternative. ?Currently it only has meaning for encoding with
> sample_fmt==SAMPLE_FMT_S32, but I think it would be better if that were
> expanded to be valid for any sample format with any raw pcm-like codec
> (ADPCM, DPCM, PCM). ?Then I think we could set that in the decoders and
> make the function return bits_per_raw_sample just for backwards
> compatibility.
>
>> The second one, av_get_bits_per_sample_fmt(), is misnamed (should be
>> av_get_bits_per_sample()), so we may change the name to
>> av_get_bits_per_sample2() for avoiding the conflict with the name
>> already taken.
>
>
> I agree. ?But as long as we're reworking it, why not
> av_get_bytes_per_sample() so it doesn't have to be divided by 8 everywhere?
>

Don't some ADPCM codecs have less than 8 bits per sample.

Regards,
Alex