avcodec/ffv1enc: Prevent generation of files with broken slices

Fixes: Ticket5548

Sponsored-by: Sovereign Tech Fund
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit b7ff66a358)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/ffv1.c

@@ -119,6 +119,13 @@ 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;
+}
+
 av_cold int ff_ffv1_init_slice_contexts(FFV1Context *f)
 {
     int max_slice_count = f->num_h_slices * f->num_v_slices;

libavcodec/ffv1.h

@@ -171,6 +171,7 @@ PlaneContext *ff_ffv1_planes_alloc(void);
 int ff_ffv1_allocate_initial_states(FFV1Context *f);
 void ff_ffv1_clear_slice_state(const FFV1Context *f, FFV1SliceContext *sc);
 int ff_ffv1_close(AVCodecContext *avctx);
+int ff_need_new_slices(int width, int num_h_slices, int chroma_shift);
 
 static av_always_inline int fold(int diff, int bits)
 {

libavcodec/ffv1enc.c

@@ -865,6 +865,10 @@ static av_cold int encode_init(AVCodecContext *avctx)
                     continue;
                 if (maxw * maxh * (int64_t)(s->bits_per_raw_sample+1) * plane_count > 8<<24)
                     continue;
+                if (s->version < 4)
+                    if (  ff_need_new_slices(avctx->width , s->num_h_slices, s->chroma_h_shift)
+                        ||ff_need_new_slices(avctx->height, s->num_v_slices, s->chroma_v_shift))
+                        continue;
                 if (avctx->slices == s->num_h_slices * s->num_v_slices && avctx->slices <= MAX_SLICES || !avctx->slices)
                     goto slices_ok;
             }