[FFmpeg-devel] [PATCH 3/3] [RFC] avcodec/ffv1: Better rounding for slice positions

[Michael Niedermayer <michael@niedermayer.cc>]

This fixes green lines in some odd dimensions with some slice configurations
like Ticket 5548

This also changes the encoder and whats encoded, and would require an
update to the specification. This change attempts to limit the change
to configurations that have missing lines currently.

Testing is welcome and needed

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
 libavcodec/ffv1.c    | 38 ++++++++++++++++++++++++++++++++++----
 libavcodec/ffv1.h    |  2 ++
 libavcodec/ffv1dec.c |  8 ++++----
 libavcodec/ffv1enc.c |  7 ++++---
 4 files changed, 44 insertions(+), 11 deletions(-)

diff --git a/libavcodec/ffv1.c b/libavcodec/ffv1.c
index f44fead350b..e780c910aee 100644
--- a/libavcodec/ffv1.c
+++ b/libavcodec/ffv1.c
@@ -103,6 +103,36 @@ av_cold int ff_ffv1_init_slices_state(FFV1Context *f)
     return 0;
 }
 
+int ff_need_new_slices(int width, int num_h_slices, int chroma_shift) {
+    int mpw = 1<<chroma_shift;
+    int i = width * (int64_t)(num_h_slices - 1) / num_h_slices;
+
+    return width % mpw && (width - i) % mpw == 0;
+}
+
+int ff_slice_coord(const FFV1Context *f, int width, int sx, int num_h_slices, int chroma_shift) {
+    int mpw = 1<<chroma_shift;
+    int awidth = FFALIGN(width, mpw);
+    int old = 1;
+
+    if (f->version > 4) {
+        old = 0;
+    } else if (f->version == 3 && f->micro_version > 4 ||
+               f->version == 4 && f->micro_version > 2
+    ) {
+        // If the old system will not encode all pixels we will choose the new
+        old = !ff_need_new_slices(width, num_h_slices, chroma_shift);
+    }
+
+    if (old)
+        return width * sx / num_h_slices;
+
+    sx = (awidth * (int64_t)sx + (num_h_slices * mpw / 2)) / (num_h_slices * mpw) * mpw;
+    if (sx == awidth)
+        sx = width;
+    return sx;
+}
+
 av_cold int ff_ffv1_init_slice_contexts(FFV1Context *f)
 {
     int i, max_slice_count = f->num_h_slices * f->num_v_slices;
@@ -112,10 +142,10 @@ av_cold int ff_ffv1_init_slice_contexts(FFV1Context *f)
     for (i = 0; i < max_slice_count;) {
         int sx          = i % f->num_h_slices;
         int sy          = i / f->num_h_slices;
-        int sxs         = f->avctx->width  *  sx      / f->num_h_slices;
-        int sxe         = f->avctx->width  * (sx + 1) / f->num_h_slices;
-        int sys         = f->avctx->height *  sy      / f->num_v_slices;
-        int sye         = f->avctx->height * (sy + 1) / f->num_v_slices;
+        int sxs         = ff_slice_coord(f, f->avctx->width , sx    , f->num_h_slices, f->chroma_h_shift);
+        int sxe         = ff_slice_coord(f, f->avctx->width , sx + 1, f->num_h_slices, f->chroma_h_shift);
+        int sys         = ff_slice_coord(f, f->avctx->height, sy   ,  f->num_v_slices, f->chroma_v_shift);
+        int sye         = ff_slice_coord(f, f->avctx->height, sy + 1, f->num_v_slices, f->chroma_v_shift);
         FFV1Context *fs = av_mallocz(sizeof(*fs));
 
         if (!fs)
diff --git a/libavcodec/ffv1.h b/libavcodec/ffv1.h
index 14e40936065..3f658a26522 100644
--- a/libavcodec/ffv1.h
+++ b/libavcodec/ffv1.h
@@ -143,6 +143,8 @@ int ff_ffv1_init_slice_contexts(FFV1Context *f);
 int ff_ffv1_allocate_initial_states(FFV1Context *f);
 void ff_ffv1_clear_slice_state(const FFV1Context *f, FFV1Context *fs);
 int ff_ffv1_close(AVCodecContext *avctx);
+int ff_need_new_slices(int width, int num_h_slices, int chroma_shift);
+int ff_slice_coord(const FFV1Context *f, int width, int sx, int num_h_slices, int chroma_shift);
 
 static av_always_inline int fold(int diff, int bits)
 {
diff --git a/libavcodec/ffv1dec.c b/libavcodec/ffv1dec.c
index a376a4c8170..0486938eb2b 100644
--- a/libavcodec/ffv1dec.c
+++ b/libavcodec/ffv1dec.c
@@ -184,10 +184,10 @@ static int decode_slice_header(const FFV1Context *f, FFV1Context *fs)
     if (sx > f->num_h_slices - sw || sy > f->num_v_slices - sh)
         return AVERROR_INVALIDDATA;
 
-    fs->slice_x      =  sx       * (int64_t)f->width  / f->num_h_slices;
-    fs->slice_y      =  sy       * (int64_t)f->height / f->num_v_slices;
-    fs->slice_width  = (sx + sw) * (int64_t)f->width  / f->num_h_slices - fs->slice_x;
-    fs->slice_height = (sy + sh) * (int64_t)f->height / f->num_v_slices - fs->slice_y;
+    fs->slice_x      =  ff_slice_coord(f, f->width , sx     , f->num_h_slices, f->chroma_h_shift);
+    fs->slice_y      =  ff_slice_coord(f, f->height, sy     , f->num_v_slices, f->chroma_v_shift);
+    fs->slice_width  =  ff_slice_coord(f, f->width , sx + sw, f->num_h_slices, f->chroma_h_shift) - fs->slice_x;
+    fs->slice_height =  ff_slice_coord(f, f->height, sy + sh, f->num_v_slices, f->chroma_v_shift) - fs->slice_y;
 
     av_assert0((unsigned)fs->slice_width  <= f->width &&
                 (unsigned)fs->slice_height <= f->height);
diff --git a/libavcodec/ffv1enc.c b/libavcodec/ffv1enc.c
index 11be7fe32ea..e04695efa93 100644
--- a/libavcodec/ffv1enc.c
+++ b/libavcodec/ffv1enc.c
@@ -397,7 +397,8 @@ static int write_extradata(FFV1Context *f)
     int i, j, k;
     uint8_t state2[32][CONTEXT_SIZE];
     unsigned v;
-
+    int need_new_slices = ff_need_new_slices(f->avctx->width , f->num_h_slices, f->chroma_h_shift)
+                        ||ff_need_new_slices(f->avctx->height, f->num_v_slices, f->chroma_v_shift);
     memset(state2, 128, sizeof(state2));
     memset(state, 128, sizeof(state));
 
@@ -412,9 +413,9 @@ static int write_extradata(FFV1Context *f)
     put_symbol(c, state, f->version, 0);
     if (f->version > 2) {
         if (f->version == 3) {
-            f->micro_version = 4;
+            f->micro_version = 4 + need_new_slices;
         } else if (f->version == 4)
-            f->micro_version = 2;
+            f->micro_version = 2 + need_new_slices;
         put_symbol(c, state, f->micro_version, 0);
     }
 
-- 
2.17.1

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