[FFmpeg-devel] [PATCH 2/2] avcodec/ffv1: Use dual run coder for fltmap

[Michael Niedermayer <michael@niedermayer.cc>]

This improves compression by 0.1% overall
I tried several other things but so far this is the best
compromise between complexity and compression

Sponsored-by: Sovereign Tech Fund
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
 libavcodec/ffv1dec_template.c | 10 ++++++++--
 libavcodec/ffv1enc_template.c | 13 +++++++++++--
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/libavcodec/ffv1dec_template.c b/libavcodec/ffv1dec_template.c
index 1fa9933d984..1f8aeb52a2d 100644
--- a/libavcodec/ffv1dec_template.c
+++ b/libavcodec/ffv1dec_template.c
@@ -159,9 +159,15 @@ static int RENAME(decode_rgb_frame)(FFV1Context *f, FFV1SliceContext *sc,
         for (int p= 0; p<3 + transparency; p++) {
             int j = 0;
             int lu = 0;
-            uint8_t state[2] = {128, 128};
+            uint8_t state[2][32];
+            int run = -1;
+            memset(state, 128, sizeof(state));
             for (int i= 0; i<65536; i++) {
-                int u = get_rac(&sc->c, state + lu);
+                int u;
+                if (run < 0)
+                    run = get_symbol_inline(&sc->c, state[lu], 0);
+                u = lu ^ !run;
+                run --;
                 sc->fltmap[p][j] = i ^ ((i&0x8000) ? 0 : 0x7FFF);
                 j+= u;
                 lu = u;
diff --git a/libavcodec/ffv1enc_template.c b/libavcodec/ffv1enc_template.c
index 4c7cd2e647c..e62fa140bee 100644
--- a/libavcodec/ffv1enc_template.c
+++ b/libavcodec/ffv1enc_template.c
@@ -177,15 +177,24 @@ static int RENAME(encode_rgb_frame)(FFV1Context *f, FFV1SliceContext *sc,
         for (int p= 0; p<3 + transparency; p++) {
             int j = 0;
             int lu = 0;
-            uint8_t state[2] = {128, 128};
+            uint8_t state[2][32];
+            int run = 0;
+            memset(state, 128, sizeof(state));
             for (int i= 0; i<65536; i++) {
                 int ri = i ^ ((i&0x8000) ? 0 : 0x7FFF);
                 int u = sc->fltmap[p][ri];
                 sc->fltmap[p][ri] = j;
                 j+= u;
-                put_rac(&sc->c, state + lu, u);
+
+                if (lu == u) {
+                    run ++;
+                } else {
+                    put_symbol_inline(&sc->c, state[lu], run, 0, NULL, NULL);
+                    run = 0;
+                }
                 lu = u;
             }
+            put_symbol(&sc->c, state[lu], run, 0);
         }
     }
 
-- 
2.48.1

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