On 2 September 2016 at 02:59, Jonathan Campbell < jonat...@impactstudiopro.com> wrote:
> I finished the consistent noise generation patch for AC-3 decoding. > > Set AVOption "cons_noisegen" to 1 (true) to enable it. > > Git repository: > https://github.com/joncampbell123/FFmpeg.git > > commit dbd086586f0ad1591ea2013293bbb6e4dbfd0455 > Author: Jonathan Campbell <jonat...@castus.tv> > Date: Thu Sep 1 18:46:16 2016 -0700 > > AC-3 consistent noise generation: avopt -cons_noisegen <number> > > When -cons_noisegen 1, the linear feedback generator used for AC-3 > dithering is seeded with the contents of the AC-3 frame. Seeding from > the AC-3 frame ensures the dithering noise comes out exactly the same > when given the same AC-3 frame data, which can then be used by > non-linear editing software to reliably decode discontinuous segments > of > an AC-3 bitstream without gaps or discontinuities. > > Jonathan Campbell > > Patch follows, hope Thunderbird doesn't garble it: > > diff --git a/libavcodec/ac3dec.c b/libavcodec/ac3dec.c > index fac189b..28048d7 100644 > --- a/libavcodec/ac3dec.c > +++ b/libavcodec/ac3dec.c > @@ -1419,6 +1419,19 @@ static int ac3_decode_frame(AVCodecContext * > avctx, void *data, > (const uint16_t *) buf, cnt); > } else > memcpy(s->input_buffer, buf, FFMIN(buf_size, > AC3_FRAME_BUFFER_SIZE)); > + > + /* if consistent noise generation is enabled, seed the linear > feedback generator > + * with the contents of the AC-3 frame so that the noise is identical > across > + * decodes given the same AC-3 frame data, for use with non-linear > edititing software. */ > + if (s->consistent_noise_generation) { > + const AVCRC *avcrc = av_crc_get_table(AV_CRC_32_IEEE); > + > + if (avcrc != NULL) > + av_lfg_init(&s->dith_state, av_crc(avcrc, 0, s->input_buffer, > FFMIN(buf_size, AC3_FRAME_BUFFER_SIZE))); > + else > + av_log(avctx, AV_LOG_ERROR, "CNG unable to seed from frame"); > + } > + > buf = s->input_buffer; > /* initialize the GetBitContext with the start of valid AC-3 Frame */ > if ((ret = init_get_bits8(&s->gbc, buf, buf_size)) < 0) > diff --git a/libavcodec/ac3dec.h b/libavcodec/ac3dec.h > index c2b867e..98184e9 100644 > --- a/libavcodec/ac3dec.h > +++ b/libavcodec/ac3dec.h > @@ -177,6 +177,10 @@ typedef struct AC3DecodeContext { > int end_freq[AC3_MAX_CHANNELS]; ///< end frequency bin > (endmant) > ///@} > > +///@name Consistent noise generation > + int consistent_noise_generation; ///< seed noise generation > with AC-3 frame on decode > +///@} > + > ///@name Rematrixing > int num_rematrixing_bands; ///< number of rematrixing > bands (nrematbnd) > int rematrixing_flags[4]; ///< rematrixing flags > (rematflg) > diff --git a/libavcodec/ac3dec_fixed.c b/libavcodec/ac3dec_fixed.c > index 6416da4..1f79ade 100644 > --- a/libavcodec/ac3dec_fixed.c > +++ b/libavcodec/ac3dec_fixed.c > @@ -168,6 +168,7 @@ static void ac3_downmix_c_fixed16(int16_t **samples, > int16_t (*matrix)[2], > #include "ac3dec.c" > > static const AVOption options[] = { > + { "cons_noisegen", "enable consistent noise generation", > OFFSET(consistent_noise_generation), AV_OPT_TYPE_BOOL, {.i64 = 0 }, 0, 1, > PAR }, > { "drc_scale", "percentage of dynamic range compression to apply", > OFFSET(drc_scale), AV_OPT_TYPE_FLOAT, {.dbl = 1.0}, 0.0, 6.0, PAR }, > { "heavy_compr", "enable heavy dynamic range compression", > OFFSET(heavy_compression), AV_OPT_TYPE_BOOL, {.i64 = 0 }, 0, 1, PAR }, > { NULL}, > diff --git a/libavcodec/ac3dec_float.c b/libavcodec/ac3dec_float.c > index 0a5319a..b85a4ce 100644 > --- a/libavcodec/ac3dec_float.c > +++ b/libavcodec/ac3dec_float.c > @@ -32,6 +32,7 @@ > #include "ac3dec.c" > > static const AVOption options[] = { > + { "cons_noisegen", "enable consistent noise generation", > OFFSET(consistent_noise_generation), AV_OPT_TYPE_BOOL, {.i64 = 0 }, 0, 1, > PAR }, > { "drc_scale", "percentage of dynamic range compression to apply", > OFFSET(drc_scale), AV_OPT_TYPE_FLOAT, {.dbl = 1.0}, 0.0, 6.0, PAR }, > { "heavy_compr", "enable heavy dynamic range compression", > OFFSET(heavy_compression), AV_OPT_TYPE_BOOL, {.i64 = 0 }, 0, 1, PAR }, > { "target_level", "target level in -dBFS (0 not applied)", > OFFSET(target_level), AV_OPT_TYPE_INT, {.i64 = 0 }, -31, 0, PAR }, > > _______________________________________________ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > http://ffmpeg.org/mailman/listinfo/ffmpeg-devel > Any random noise, hardcoded constant or not sill sounds like white noise. What is the point of this patch? _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
