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

[Justin Ruggles]

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?

-Justin