[FFmpeg-cvslog] avcodec/ac3dec: add consistent noise generation option.

Jonathan Campbell git at videolan.org
Sun Jan 22 03:31:01 EET 2017


ffmpeg | branch: master | Jonathan Campbell <jonathan at castus.tv> | Sat Sep  3 03:34:01 2016 -0700| [d5d474aea53822642f0465825f8a94cb2327e1e6] | committer: Michael Niedermayer

avcodec/ac3dec: add consistent noise generation option.

use av_lfg_init_from_data() to seed AC-3 dithering from the AC-3 frame
data to make it consistent given the same AC-3 frame, if option is set.

Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=d5d474aea53822642f0465825f8a94cb2327e1e6
---

 libavcodec/ac3dec.c       | 7 +++++++
 libavcodec/ac3dec.h       | 4 ++++
 libavcodec/ac3dec_fixed.c | 1 +
 libavcodec/ac3dec_float.c | 1 +
 4 files changed, 13 insertions(+)

diff --git a/libavcodec/ac3dec.c b/libavcodec/ac3dec.c
index 499971a..4499160 100644
--- a/libavcodec/ac3dec.c
+++ b/libavcodec/ac3dec.c
@@ -1426,6 +1426,13 @@ 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)
+        av_lfg_init_from_data(&s->dith_state, s->input_buffer, FFMIN(buf_size, AC3_FRAME_BUFFER_SIZE));
+
     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 6cd67c0..495e9a6 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 },



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