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

[Lance Wang]

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



> 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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