[FFmpeg-devel] [RFC] LPCM 24 bits support

[Michael Niedermayer]

On Fri, Apr 18, 2008 at 11:24:03PM +0200, Lars T?uber wrote:
> On Fri, 18 Apr 2008 22:52:40 +0200 Michael Niedermayer <michaelni at gmx.at> wrote:
> > On Fri, Apr 18, 2008 at 09:37:12PM +0200, Lars T?uber wrote:
> > > On Fri, 18 Apr 2008 22:08:24 +0200 Michael Niedermayer <michaelni at gmx.at> wrote:
> > > > On Fri, Apr 18, 2008 at 09:05:23PM +0200, Lars T?uber wrote:
> > > > > On Fri, 18 Apr 2008 15:39:43 +0200 Michael Niedermayer <michaelni at gmx.at> wrote:
> > > > > > On Thu, Apr 17, 2008 at 10:13:40PM +0200, Lars T?uber wrote:
> [...]
> > > @@ -492,6 +498,35 @@ static int pcm_decode_frame(AVCodecConte
> > >              *samples++ = s->table[*src++];
> > >          }
> > >          break;
> > > +    case CODEC_ID_PCM_DVD: {
> > > +            int audio24[8*2], *ap;
> > > +            const uint8_t *src_LSB;
> > > +
> > > +            if (avctx->channels <= 0 || avctx->channels > 8) {
> > > +                av_log(avctx, AV_LOG_ERROR, "PCM_DVD channels out of bounds\n");
> > > +                return -1;
> > > +            }
> > > +            n = buf_size / (avctx->channels * 2 * avctx->bits_per_sample / 8);
> > > +            while (n--) {
> > > +                ap = audio24;
> > > +                src_LSB = src + avctx->channels * 2 * 2;
> > > +
> > > +                if (avctx->bits_per_sample == 20)
> > > +                    for (c=0; c < avctx->channels; c++, src+=4, src_LSB++ ) {
> > > +                        *ap++ = src[0]<<16 | src[1]<<8 | (*src_LSB & 0xf0);
> > > +                        *ap++ = src[2]<<16 | src[3]<<8 | (*src_LSB & 0x0f)<<4;
> > > +                    }
> > > +                else {
> > > +                    for (c=0; c < 2*avctx->channels; c++, src+=2, src_LSB++ )
> > > +                        *ap++ = src[0]<<16 | src[1]<<8 | *src_LSB;
> > > +                }
> > > +                src = src_LSB;
> > > +
> > > +                for (c=0; c < avctx->channels*2; c++)
> > > +                    *samples++ = audio24[c] >> 8;
> > > +            }
> > 
> > and what if bits_per_sample is something else than 20 or 24 ?
> 
> Switch statement added.
> 
> I'm not sure about the wording of the error message.
> Is it
> - sample depth
> - sample width or
> - sample resolution
> ???

all are fine


[...]
> diff -pur ffmpeg/libavcodec/pcm.c ffmpeg.1/libavcodec/pcm.c
> --- ffmpeg/libavcodec/pcm.c	2008-04-18 20:22:18.000000000 +0200
> +++ ffmpeg.1/libavcodec/pcm.c	2008-04-18 23:19:20.000000000 +0200
> @@ -492,6 +498,41 @@ static int pcm_decode_frame(AVCodecConte
>              *samples++ = s->table[*src++];
>          }
>          break;
> +    case CODEC_ID_PCM_DVD: {
> +            int audio24[8*2], *ap;
> +            const uint8_t *src_LSB;
> +
> +            if (avctx->channels > 8) {
> +                av_log(avctx, AV_LOG_ERROR, "PCM_DVD channels out of bounds\n");
> +                return -1;
> +            }

> +            n = buf_size / (avctx->channels * 2 * avctx->bits_per_sample / 8);
> +            while (n--) {
> +                ap = audio24;
> +                src_LSB = src + avctx->channels * 2 * 2;
> +
> +                switch (avctx->bits_per_sample) {
> +                    case 20:
> +                        for (c=0; c < avctx->channels; c++, src+=4, src_LSB++ ) {
> +                            *ap++ = src[0]<<16 | src[1]<<8 | (*src_LSB & 0xf0);
> +                            *ap++ = src[2]<<16 | src[3]<<8 | (*src_LSB & 0x0f)<<4;
> +                        }
> +                        break;
> +                    case 24:
> +                        for (c=0; c < 2*avctx->channels; c++, src+=2, src_LSB++ )
> +                            *ap++ = src[0]<<16 | src[1]<<8 | *src_LSB;
> +                        break;
> +                    default:
> +                        av_log(avctx, AV_LOG_ERROR, "PCM_DVD unsupported sample depth\n");
> +                        return -1;
> +                }
> +                src = src_LSB;
> +
> +                for (c=0; c < avctx->channels*2; c++)
> +                    *samples++ = audio24[c] >> 8;

following is simpler and faster:

if(avctx->bits_per_sample != 20 && avctx->bits_per_sample != 24){
    av_log(avctx, AV_LOG_ERROR, "PCM_DVD unsupported sample depth\n");
    return -1;
}
n = buf_size / (avctx->channels * 2 * avctx->bits_per_sample / 8);
while (n--) {
    for (c=0; c < 2*avctx->channels; c++)
        *samples++ = bytestream_get_be16(&src);
    src+= avctx->channels * (avctx->bits_per_sample-16) / 4;
}

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

No snowflake in an avalanche ever feels responsible. -- Voltaire
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