[FFmpeg-devel] [PATCH 4/4] avcodec/ffv1: NOT FOR GIT, experiment about float decorrelation

[Michael Niedermayer <michael@niedermayer.cc>]

This performs a tiny bit better than not using it but it is incompatible
with the RCT which gives a bigger gain

Sponsored-by: Sovereign Tech Fund
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
 libavcodec/ffv1.h             | 20 ++++++++++++++++++++
 libavcodec/ffv1enc_template.c | 33 ++++++++++++++++++++++++---------
 2 files changed, 44 insertions(+), 9 deletions(-)

diff --git a/libavcodec/ffv1.h b/libavcodec/ffv1.h
index 2c2df154037..84a443613df 100644
--- a/libavcodec/ffv1.h
+++ b/libavcodec/ffv1.h
@@ -196,6 +196,26 @@ static av_always_inline int fold(int diff, int bits)
     return diff;
 }
 
+// We treat infinite as a big number, 0 as a small non 0 number, this is close enough, we ignore denormal numbers
+static av_always_inline int64_t f2i(uint16_t f)
+{
+    int s = -(f>>15);
+    int64_t v = (1024L + (f & 1023)) << ((f & 0x7C00) >> 10);
+    return (v + s) ^ s;
+}
+
+//undo above
+static av_always_inline uint16_t i2f(int64_t v)
+{
+    int s = v>>63;
+    int e;
+    v = (v + s) ^ s;
+
+    e = av_log2(v>>10);
+
+    return (s&32768) + (e<<10) + ((v + (1U<<e)/2) >> e) - 1024;
+}
+
 static inline void update_vlc_state(VlcState *const state, const int v)
 {
     int drift = state->drift;
diff --git a/libavcodec/ffv1enc_template.c b/libavcodec/ffv1enc_template.c
index bc14926ab95..12d519320c0 100644
--- a/libavcodec/ffv1enc_template.c
+++ b/libavcodec/ffv1enc_template.c
@@ -64,7 +64,13 @@ RENAME(encode_line)(FFV1Context *f, FFV1SliceContext *sc,
 
         context = RENAME(get_context)(f->quant_tables[p->quant_table_index],
                                       sample[0] + x, sample[1] + x, sample[2] + x);
-        diff    = sample[0][x] - RENAME(predict)(sample[0] + x, sample[1] + x);
+
+        int64_t  L = f2i(sample[0][x-1]);
+        int64_t  T = f2i(sample[1][x]);
+        int64_t LT = f2i(sample[1][x-1]);
+
+        diff    = sample[0][x] - mid_pred(i2f(L), i2f(L + T - LT), i2f(T));
+//         diff    = sample[0][x] - RENAME(predict)(sample[0] + x, sample[1] + x);
 
         if (context < 0) {
             context = -context;
@@ -147,7 +153,16 @@ 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(0){
+        int v;
+        for (v = 0; v<65536; v++) {
+            int64_t i = f2i(v);
+            int v2 = i2f(i);
+            if (v != v2)
+                av_log(0,0, "D %X %X %LX\n", v, v2, i);
+            av_assert0(v2 == v);
+        }
+    }
     for (y = 0; y < h; y++) {
         for (i = 0; i < ring_size; i++)
             for (p = 0; p < MAX_PLANES; p++)
@@ -180,13 +195,13 @@ static int RENAME(encode_rgb_frame)(FFV1Context *f, FFV1SliceContext *sc,
                 r = *((const uint16_t *)(src[2] + x*2 + stride[2]*y));
             }
 
-            if (sc->slice_coding_mode != 1) {
-                b -= g;
-                r -= g;
-                g += (b * sc->slice_rct_by_coef + r * sc->slice_rct_ry_coef) >> 2;
-                b += offset;
-                r += offset;
-            }
+//             if (sc->slice_coding_mode != 1) {
+//                 b -= g;
+//                 r -= g;
+//                 g += (b * sc->slice_rct_by_coef + r * sc->slice_rct_ry_coef) >> 2;
+//                 b += offset;
+//                 r += offset;
+//             }
 
             sample[0][0][x] = g;
             sample[1][0][x] = b;
-- 
2.48.1

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