[FFmpeg-devel] [RFC/PATCH] bitpacked_dec: Optimization for bitpacked_dec decoder performance

[Paul B Mahol]

On Sat, May 6, 2023 at 1:32 PM Lance Wang <lance.lmwang at gmail.com> wrote:

> On Sat, May 6, 2023 at 4:58 AM Devin Heitmueller <
> devin.heitmueller at ltnglobal.com> wrote:
>
> > Rework the code a bit to speed up the 10-bit bitpacked decoding
> > routine.  This is probably about as fast as I can get it without
> > switching to assembly language.
> >
> > Demonstratable with:
> >
> > ./ffmpeg -f lavfi -i "smptehdbars=size=3840x2160" -c bitpacked -f image2
> > -frames:v 1 source.yuv
> > ./ffmpeg -f bitpacked -pix_fmt yuv422p10le -s 3840x2160 -c:v bitpacked -i
> > source.yuv -pix_fmt yuv422p10le out.yuv
> >
> > On my development system, it went from 80ms for a 2160p frame
> > down to 20ms (i.e. a 4X speedup).  Good enough for now, I hope...
> >
> >
> FYI, on my development system, I run two time for the original and modified
> version and no obvious difference:
> ./ffmpeg -f lavfi -i "smptehdbars=size=3840x2160" -c bitpacked -frames:v 25
> source.yuv
> time ./ffmpeg -f bitpacked -pix_fmt yuv422p10le -s 3840x2160 -c:v bitpacked
> -i source.yuv -pix_fmt yuv422p10le out.yuv
> frame=   25 fps=0.0 q=-0.0 Lsize=  810000kB time=00:00:00.96
> bitrate=6912000.0kbits/s speed=1.13x
>
> real 0m0.961s
> user 0m1.086s
> sys 0m1.360s
>
> frame=   25 fps=0.0 q=-0.0 Lsize=  810000kB time=00:00:00.96
> bitrate=6912000.0kbits/s speed=1.16x
>
> real 0m0.936s
> user 0m1.358s
> sys 0m1.350s
>
> after apply the patch:
> frame=   25 fps=0.0 q=-0.0 Lsize=  810000kB time=00:00:00.96
> bitrate=6912000.0kbits/s speed=1.14x
>
> real 0m0.953s
> user 0m0.906s
> sys 0m1.438s
>
> frame=   25 fps=0.0 q=-0.0 Lsize=  810000kB time=00:00:00.96
> bitrate=6912000.0kbits/s speed=1.17x
>
> real 0m0.922s
> user 0m0.926s
> sys 0m1.066s
>

Only 25 frames?
This is flawed.


>
>
>
> > Signed-off-by: Devin Heitmueller <dheitmueller at ltnglobal.com>
> > ---
> >  libavcodec/bitpacked_dec.c | 17 +++++++----------
> >  1 file changed, 7 insertions(+), 10 deletions(-)
> >
> > diff --git a/libavcodec/bitpacked_dec.c b/libavcodec/bitpacked_dec.c
> > index a1ffef1..96aba27 100644
> > --- a/libavcodec/bitpacked_dec.c
> > +++ b/libavcodec/bitpacked_dec.c
> > @@ -28,7 +28,6 @@
> >
> >  #include "avcodec.h"
> >  #include "codec_internal.h"
> > -#include "get_bits.h"
> >  #include "libavutil/imgutils.h"
> >  #include "thread.h"
> >
> > @@ -65,7 +64,7 @@ static int bitpacked_decode_yuv422p10(AVCodecContext
> > *avctx, AVFrame *frame,
> >  {
> >      uint64_t frame_size = (uint64_t)avctx->width *
> > (uint64_t)avctx->height * 20;
> >      uint64_t packet_size = (uint64_t)avpkt->size * 8;
> > -    GetBitContext bc;
> > +    uint8_t *src;
> >      uint16_t *y, *u, *v;
> >      int ret, i, j;
> >
> > @@ -79,20 +78,18 @@ static int bitpacked_decode_yuv422p10(AVCodecContext
> > *avctx, AVFrame *frame,
> >      if (avctx->width % 2)
> >          return AVERROR_PATCHWELCOME;
> >
> > -    ret = init_get_bits(&bc, avpkt->data, avctx->width * avctx->height *
> > 20);
> > -    if (ret)
> > -        return ret;
> > -
> > +    src = avpkt->data;
> >      for (i = 0; i < avctx->height; i++) {
> >          y = (uint16_t*)(frame->data[0] + i * frame->linesize[0]);
> >          u = (uint16_t*)(frame->data[1] + i * frame->linesize[1]);
> >          v = (uint16_t*)(frame->data[2] + i * frame->linesize[2]);
> >
> >          for (j = 0; j < avctx->width; j += 2) {
> > -            *u++ = get_bits(&bc, 10);
> > -            *y++ = get_bits(&bc, 10);
> > -            *v++ = get_bits(&bc, 10);
> > -            *y++ = get_bits(&bc, 10);
> > +            *u++ = (src[0] << 2) | (src[1] >> 6);
> > +            *y++ = ((src[1] << 4) | (src[2] >> 4)) & 0x3ff;
> > +            *v++ = ((src[2] << 6) | (src[3] >> 2)) & 0x3ff;
> > +            *y++ = ((src[3] << 8) | (src[4]))      & 0x3ff;
> > +            src += 5;
> >          }
> >      }
> >
> > --
> > 1.8.3.1
> >
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