[FFmpeg-devel] [PATCH] Deterministic Noise Generation option for audio codecs that involve noise generation (RNG)

[Michael Niedermayer]

On Sat, Sep 07, 2013 at 01:24:03PM -0700, Jonathan Campbell wrote:
> Here you go.
> 
> This patch adds:
> 
> -a function to libavutil's linear feedback generator to initialize a
> known state from binary data and a frame counter value.
> - two flags to libavcodec/avcodec.h to enable deterministic noise
> generation and another flag to be implemented in the future to
> disable noise band coding entirely.
> - two lines of code to ac3dec.c to seed the LFG on decode to the
> AC-3 frame and the AVContext frame number.
> 
> It is written to patch against FFMPEG 1.2.3. Do you need me to make
> another patch for FFMPEG 2.0.1 or can you guys handle that?

patches must be against git master or rather they have to apply to
git master and work.
releases only receive backports from master.

more comments below
[...]

> 671cd059b5d1446f2dbc8905bdd6ddef3f23cf02  ffmpeg-1.2.3-codec-flag2-dng.patch
> diff -r -u ffmpeg-1.2.3.old/libavcodec/ac3dec.c ffmpeg-1.2.3/libavcodec/ac3dec.c
> --- ffmpeg-1.2.3.old/libavcodec/ac3dec.c	2013-08-26 17:13:44.000000000 -0700
> +++ ffmpeg-1.2.3/libavcodec/ac3dec.c	2013-09-07 12:50:45.194293510 -0700
> @@ -1380,6 +1380,10 @@
>          return ret;
>      }
>  
> +    /* if Deterministic Noise Generation is enabled, then seed the RNG from the input frame */
> +    if (avctx->flags2 & CODEC_FLAG2_DNG)

> +	av_lfg_init_from_binary_data_and_frame_number(&s->dith_state,buf,s->frame_size,avctx->frame_number);

tabs are not allowed in ffmpeg git (except in Makefiles)


> +
>      /* decode the audio blocks */
>      channel_map = ff_ac3_dec_channel_map[s->output_mode & ~AC3_OUTPUT_LFEON][s->lfe_on];
>      for (ch = 0; ch < AC3_MAX_CHANNELS; ch++) {
> diff -r -u ffmpeg-1.2.3.old/libavcodec/avcodec.h ffmpeg-1.2.3/libavcodec/avcodec.h
> --- ffmpeg-1.2.3.old/libavcodec/avcodec.h	2013-08-26 17:13:44.000000000 -0700
> +++ ffmpeg-1.2.3/libavcodec/avcodec.h	2013-09-07 12:53:11.816875961 -0700
> @@ -718,6 +718,8 @@
>  #define CODEC_FLAG2_LOCAL_HEADER  0x00000008 ///< Place global headers at every keyframe instead of in extradata.
>  #define CODEC_FLAG2_DROP_FRAME_TIMECODE 0x00002000 ///< timecode is in drop frame format. DEPRECATED!!!!
>  #define CODEC_FLAG2_IGNORE_CROP   0x00010000 ///< Discard cropping information from SPS.
> +#define CODEC_FLAG2_DNG           0x00020000 ///< Enable Deterministic Noise Generation.
> +#define CODEC_FLAG2_NO_NOISE      0x00040000 ///< Disable noise coding (XXX not yet implemented)

please dont add any flags, the flag systems is rather unflexible and
the number of flags limited to 32


>  
>  #if FF_API_MPV_GLOBAL_OPTS
>  #define CODEC_FLAG_CBP_RD         0x04000000 ///< Use rate distortion optimization for cbp.
> diff -r -u ffmpeg-1.2.3.old/libavutil/lfg.c ffmpeg-1.2.3/libavutil/lfg.c
> --- ffmpeg-1.2.3.old/libavutil/lfg.c	2013-08-10 16:23:28.000000000 -0700
> +++ ffmpeg-1.2.3/libavutil/lfg.c	2013-09-07 12:51:04.334630770 -0700
> @@ -44,6 +44,26 @@
>      c->index = 0;
>  }
>  
> +av_cold void av_lfg_init_from_binary_data_and_frame_number(AVLFG *c, unsigned char *data,unsigned int data_length,unsigned int counter)
> +{
> +    uint8_t tmp[16] = { 0 };
> +    int i;
> +
> +    av_md5_sum(tmp, data, data_length);
> +    for (i = 8; i < 64; i += 4) {
> +        c->state[i    ] = AV_RL32(tmp);
> +        c->state[i + 1] = AV_RL32(tmp + 4);
> +        c->state[i + 2] = AV_RL32(tmp + 8);
> +        c->state[i + 3] = AV_RL32(tmp + 12);
> +	if (i != 60) {
> +            tmp[4] = i;
> +	    if (counter != 0 && (i&1) == 0) AV_WL32(tmp+6,counter); /* XXX: Is there a better way? */
> +	    av_md5_sum(tmp, tmp, 16);
> +	}
> +    }

md5 is slow, running it over the whole frame is overkill
libavutil/murmur3.c might be an alternative

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Asymptotically faster algorithms should always be preferred if you have
asymptotical amounts of data
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