* [FFmpeg-devel] [PATCH 1/2] avcodec/ffv1: flip half of float16
@ 2025-01-18 20:19 Michael Niedermayer
2025-01-18 20:19 ` [FFmpeg-devel] [PATCH 2/2] avcodec/ffv1: Compactify floats Michael Niedermayer
0 siblings, 1 reply; 2+ messages in thread
From: Michael Niedermayer @ 2025-01-18 20:19 UTC (permalink / raw)
To: FFmpeg development discussions and patches
float16 is a sign bit followed by "positive is larger" exponent and mantisse
that way the up direction changes between negative and positive numbers
flipping the exponent and mantisse for positive numbers gives a compression
gain of 0.5% for both RCT and noRCT modes using the
ACES_OT_VWG_SampleFrames testset
Sponsored-by: Sovereign Tech Fund
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
libavcodec/ffv1dec_template.c | 10 ++++++++++
libavcodec/ffv1enc_template.c | 11 +++++++++++
2 files changed, 21 insertions(+)
diff --git a/libavcodec/ffv1dec_template.c b/libavcodec/ffv1dec_template.c
index e983d1ba648..0be17b54bbb 100644
--- a/libavcodec/ffv1dec_template.c
+++ b/libavcodec/ffv1dec_template.c
@@ -185,6 +185,16 @@ static int RENAME(decode_rgb_frame)(FFV1Context *f, FFV1SliceContext *sc,
b += g;
r += g;
}
+ if (f->flt) {
+ if (!(r&0x8000))
+ r ^= 0x7FFF;
+ if (!(g&0x8000))
+ g ^= 0x7FFF;
+ if (!(b&0x8000))
+ b ^= 0x7FFF;
+ if (transparency && !(a&0x8000))
+ a ^= 0x7FFF;
+ }
if (lbd)
*((uint32_t*)(src[0] + x*4 + stride[0]*y)) = b + ((unsigned)g<<8) + ((unsigned)r<<16) + ((unsigned)a<<24);
diff --git a/libavcodec/ffv1enc_template.c b/libavcodec/ffv1enc_template.c
index bc14926ab95..4d20cb93627 100644
--- a/libavcodec/ffv1enc_template.c
+++ b/libavcodec/ffv1enc_template.c
@@ -180,6 +180,17 @@ static int RENAME(encode_rgb_frame)(FFV1Context *f, FFV1SliceContext *sc,
r = *((const uint16_t *)(src[2] + x*2 + stride[2]*y));
}
+ if (f->flt) {
+ if (!(r&0x8000))
+ r ^= 0x7FFF;
+ if (!(g&0x8000))
+ g ^= 0x7FFF;
+ if (!(b&0x8000))
+ b ^= 0x7FFF;
+ if (transparency && !(a&0x8000))
+ a ^= 0x7FFF;
+ }
+
if (sc->slice_coding_mode != 1) {
b -= g;
r -= g;
--
2.48.1
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^ permalink raw reply [flat|nested] 2+ messages in thread
* [FFmpeg-devel] [PATCH 2/2] avcodec/ffv1: Compactify floats
2025-01-18 20:19 [FFmpeg-devel] [PATCH 1/2] avcodec/ffv1: flip half of float16 Michael Niedermayer
@ 2025-01-18 20:19 ` Michael Niedermayer
0 siblings, 0 replies; 2+ messages in thread
From: Michael Niedermayer @ 2025-01-18 20:19 UTC (permalink / raw)
To: FFmpeg development discussions and patches
float16 (and more so float32) have many odd values
half the values are negative, many are larger than "1.0"
and many values are very close to 0.
Storing the 16bits as is, looses compression because of the mixture
of dense and sparse regions and also many completely unused ones.
This simply remaps the 65536 values so no unused values remain
This improves compression by about 1% for the ACES_OT_VWG_SampleFrames testset
(this testset contains all kind of funny values including many images
with negative rgb values)
The space needed for the map is insignificant compared to the
compression gained
Sponsored-by: Sovereign Tech Fund
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
libavcodec/ffv1.h | 1 +
libavcodec/ffv1dec_template.c | 20 +++++++++++++
libavcodec/ffv1enc_template.c | 54 +++++++++++++++++++++++++++++++++++
3 files changed, 75 insertions(+)
diff --git a/libavcodec/ffv1.h b/libavcodec/ffv1.h
index 2c2df154037..bf49f613a75 100644
--- a/libavcodec/ffv1.h
+++ b/libavcodec/ffv1.h
@@ -104,6 +104,7 @@ typedef struct FFV1SliceContext {
uint64_t (*rc_stat2[MAX_QUANT_TABLES])[32][2];
};
};
+ uint16_t fltmap[4][65536];
} FFV1SliceContext;
typedef struct FFV1Context {
diff --git a/libavcodec/ffv1dec_template.c b/libavcodec/ffv1dec_template.c
index 0be17b54bbb..4662ec51651 100644
--- a/libavcodec/ffv1dec_template.c
+++ b/libavcodec/ffv1dec_template.c
@@ -155,6 +155,20 @@ static int RENAME(decode_rgb_frame)(FFV1Context *f, FFV1SliceContext *sc,
memset(RENAME(sc->sample_buffer), 0, 8 * (w + 6) * sizeof(*RENAME(sc->sample_buffer)));
+ if (f->flt) {
+ for (int p= 0; p<3 + transparency; p++) {
+ int j = 0;
+ int lu = 0;
+ uint8_t state[2] = {128, 128};
+ for (int i= 0; i<65536; i++) {
+ int u = get_rac(&sc->c, state + lu);
+ sc->fltmap[p][j] = i;
+ j+= u;
+ lu = u;
+ }
+ }
+ }
+
for (y = 0; y < h; y++) {
for (p = 0; p < 3 + transparency; p++) {
int ret;
@@ -186,6 +200,12 @@ static int RENAME(decode_rgb_frame)(FFV1Context *f, FFV1SliceContext *sc,
r += g;
}
if (f->flt) {
+ r = sc->fltmap[0][r];
+ g = sc->fltmap[1][g];
+ b = sc->fltmap[2][b];
+ if (transparency)
+ a = sc->fltmap[3][a];
+
if (!(r&0x8000))
r ^= 0x7FFF;
if (!(g&0x8000))
diff --git a/libavcodec/ffv1enc_template.c b/libavcodec/ffv1enc_template.c
index 4d20cb93627..da81a6a44ac 100644
--- a/libavcodec/ffv1enc_template.c
+++ b/libavcodec/ffv1enc_template.c
@@ -148,6 +148,54 @@ static int RENAME(encode_rgb_frame)(FFV1Context *f, FFV1SliceContext *sc,
memset(RENAME(sc->sample_buffer), 0, ring_size * MAX_PLANES *
(w + 6) * sizeof(*RENAME(sc->sample_buffer)));
+ if (f->flt) {
+ memset(sc->fltmap, 0, sizeof(sc->fltmap));
+
+ for (y = 0; y < h; y++) {
+ for (x = 0; x < w; x++) {
+ int b, g, r, av_uninit(a);
+
+ if (sizeof(TYPE) == 4 || transparency) {
+ g = *((const uint16_t *)(src[0] + x*2 + stride[0]*y));
+ b = *((const uint16_t *)(src[1] + x*2 + stride[1]*y));
+ r = *((const uint16_t *)(src[2] + x*2 + stride[2]*y));
+ if (transparency)
+ a = *((const uint16_t *)(src[3] + x*2 + stride[3]*y));
+ } else {
+ b = *((const uint16_t *)(src[0] + x*2 + stride[0]*y));
+ g = *((const uint16_t *)(src[1] + x*2 + stride[1]*y));
+ r = *((const uint16_t *)(src[2] + x*2 + stride[2]*y));
+ }
+ if (!(r&0x8000))
+ r ^= 0x7FFF;
+ if (!(g&0x8000))
+ g ^= 0x7FFF;
+ if (!(b&0x8000))
+ b ^= 0x7FFF;
+ if (transparency && !(a&0x8000))
+ a ^= 0x7FFF;
+
+ sc->fltmap[0][r] = 1;
+ sc->fltmap[1][g] = 1;
+ sc->fltmap[2][b] = 1;
+ if (transparency)
+ sc->fltmap[3][a] = 1;
+ }
+ }
+ for (int p= 0; p<3 + transparency; p++) {
+ int j = 0;
+ int lu = 0;
+ uint8_t state[2] = {128, 128};
+ for (int i= 0; i<65536; i++) {
+ int u = sc->fltmap[p][i];
+ sc->fltmap[p][i] = j;
+ j+= u;
+ put_rac(&sc->c, state + lu, u);
+ lu = u;
+ }
+ }
+ }
+
for (y = 0; y < h; y++) {
for (i = 0; i < ring_size; i++)
for (p = 0; p < MAX_PLANES; p++)
@@ -189,6 +237,12 @@ static int RENAME(encode_rgb_frame)(FFV1Context *f, FFV1SliceContext *sc,
b ^= 0x7FFF;
if (transparency && !(a&0x8000))
a ^= 0x7FFF;
+
+ r = sc->fltmap[0][r];
+ g = sc->fltmap[1][g];
+ b = sc->fltmap[2][b];
+ if (transparency)
+ a = sc->fltmap[3][a];
}
if (sc->slice_coding_mode != 1) {
--
2.48.1
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https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
To unsubscribe, visit link above, or email
ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".
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2025-01-18 20:19 [FFmpeg-devel] [PATCH 1/2] avcodec/ffv1: flip half of float16 Michael Niedermayer
2025-01-18 20:19 ` [FFmpeg-devel] [PATCH 2/2] avcodec/ffv1: Compactify floats Michael Niedermayer
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