[FFmpeg-devel] CNG (consistent noise generation) patch for AC-3 decoder
Jonathan Campbell
jonathan at impactstudiopro.com
Sat Sep 3 02:49:54 EEST 2016
On 09/02/2016 04:37 PM, Michael Niedermayer wrote:
> On Fri, Sep 02, 2016 at 04:05:44PM -0700, Jonathan Campbell wrote:
>> On 09/02/2016 01:56 PM, Michael Niedermayer wrote:
>>> On Fri, Sep 02, 2016 at 01:13:33PM -0700, Jonathan Campbell wrote:
>>>> On 09/02/2016 01:01 PM, Michael Niedermayer wrote:
>>>>> On Fri, Sep 02, 2016 at 10:19:23AM -0700, Jonathan Campbell wrote:
>>>>> [...]
>>>>>> CRC computation isn't fast enough? What should I use then? A sum of
>>>>>> byte values?
>>>>> av_lfg_init() calls av_md5_sum()
>>>>> av_md5_sum() is too slow to be called per ac3 frame
>>>>>
>>>>> [...]
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> ffmpeg-devel mailing list
>>>>> ffmpeg-devel at ffmpeg.org
>>>>> http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>>>> Then for this to work at better performance, I'm going to have to
>>>> either directly modify the AVLFG struct state (probably not a good
>>>> idea), or add a function to libavutil/lfg.c that allows "fast
>>>> seeding" without the use of MD5 which could probably be something as
>>>> simple as copy the 32-bit seed 16 times through c->state[] with or
>>>> without modification during the loop. Sound good?
>>> yes, something like this
>>> probably spliting the input into 16 parts get 16 CRCs and use them
>>> instead of replication is probably better
>>>
>>>
>>> [...]
>>>
>>>
>>> _______________________________________________
>>> ffmpeg-devel mailing list
>>> ffmpeg-devel at ffmpeg.org
>>> http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>> How's this:
>>
>> void av_lfg_init_from_data(AVLFG *c, const unsigned char *data,
>> unsigned int length) {
>> unsigned int beg, end, segm;
>> const AVCRC *avcrc;
>> uint32_t crc = 0;
> 1 might be better
>
> should be ok otherwise didnt review it deeply though
>
> [...]
>
>
> _______________________________________________
> ffmpeg-devel mailing list
> ffmpeg-devel at ffmpeg.org
> http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
Finished patch. Hopefully it won't get garbled as an attachment.
Jonathan Campbell
-------------- next part --------------
diff --git a/libavcodec/ac3dec.c b/libavcodec/ac3dec.c
index fac189b..18a674b 100644
--- a/libavcodec/ac3dec.c
+++ b/libavcodec/ac3dec.c
@@ -1419,6 +1419,13 @@ 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 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 },
diff --git a/libavutil/lfg.c b/libavutil/lfg.c
index 08a4f67..178d27e 100644
--- a/libavutil/lfg.c
+++ b/libavutil/lfg.c
@@ -23,6 +23,7 @@
#include <limits.h>
#include <math.h>
#include "lfg.h"
+#include "crc.h"
#include "md5.h"
#include "intreadwrite.h"
#include "attributes.h"
@@ -58,3 +59,29 @@ void av_bmg_get(AVLFG *lfg, double out[2])
out[0] = x1 * w;
out[1] = x2 * w;
}
+
+void av_lfg_init_from_data(AVLFG *c, const unsigned char *data, unsigned int length) {
+ unsigned int beg, end, segm;
+ const AVCRC *avcrc;
+ uint32_t crc = 1;
+
+ c->index = 0;
+
+ avcrc = av_crc_get_table(AV_CRC_32_IEEE);
+ if (avcrc == NULL) return;
+
+ /* try to avoid integer overflow during the segmented crc loop below.
+ * the code below would break if "end" went backwards before "beg". */
+ if (length > (UINT_MAX / 128U)) return;
+
+ /* across 64 pieces of the incoming data,
+ * do a running crc of each segment and store the crc as the state for that slot.
+ * this works even if the length of the piece is 0 bytes. */
+ beg = 0;
+ for (segm = 0;segm < 64;segm++) {
+ end = (((segm + 1) * length) / 64);
+ crc = av_crc(avcrc, crc, data + beg, end - beg);
+ c->state[segm] = (unsigned int)crc;
+ beg = end;
+ }
+}
diff --git a/libavutil/lfg.h b/libavutil/lfg.h
index ec90562..f3c08ec 100644
--- a/libavutil/lfg.h
+++ b/libavutil/lfg.h
@@ -29,6 +29,11 @@ typedef struct AVLFG {
void av_lfg_init(AVLFG *c, unsigned int seed);
+/*
+ * Seed the state of the ALFG using binary data
+ */
+void av_lfg_init_from_data(AVLFG *c, const unsigned char *data, unsigned int length);
+
/**
* Get the next random unsigned 32-bit number using an ALFG.
*
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