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@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@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@ffmpeg.org
http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
Finished patch. Hopefully it won't get garbled as an attachment.
Jonathan Campbell
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.
*
_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel@ffmpeg.org
http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
