On date Tuesday 2023-12-26 23:25:16 +0100, Clément Bœsch wrote: > These functions encode a slice of alpha (1 to 8 macroblocks) which are > expected to be encoded as a repeated sequence of "[diff][run-1]", where > diff is the running difference of the alpha value and run is how many > times that value is expected to be duplicated (within the limit of a > grand total of 2048 unpacked samples, corresponding to a slice of 8 MB). > > Even when run==0 (the run variable semantic is actually "run minus 1"), > there is always a diff previously encoded that needs a counter of at > least 1. This means we need to call put_alpha_run() unconditionally at > the end of the bitstream to account for the last running diff. > > This commit fixes glitchy playbacks on QuickTime with M2 and M3 hardware > (but not M1 for some mysterious reason) with files generated with > commands such as: > > ffmpeg -f lavfi -i testsrc2=d=5:s=912x320,chromakey -c:v prores_aw > -profile:v 4 -y aw.mov > ffmpeg -f lavfi -i testsrc2=d=5:s=912x320,chromakey -c:v prores_ks > -profile:v 4444 -y ks.mov > > The glitch expresses itself deterministically as blinking black > rectangles on random frames (for example on frame 21, 54, 71, 79, ...). > > Even with the proresdec from FFmpeg, overreads actually happens while > reading the run-minus-1 value (around val = get_bits(gb, 4) in > unpack_alpha()). This doesn't seem to cause any particular issue because > it simply overreads into the next slice, and because the decoder is > resilient, but it's still a problem. > > Fixes ticket #10255. > --- > libavcodec/proresenc_anatoliy.c | 3 +-- > libavcodec/proresenc_kostya.c | 3 +-- > 2 files changed, 2 insertions(+), 4 deletions(-) > > diff --git a/libavcodec/proresenc_anatoliy.c b/libavcodec/proresenc_anatoliy.c > index 16741afd68..9b9ffa03be 100644 > --- a/libavcodec/proresenc_anatoliy.c > +++ b/libavcodec/proresenc_anatoliy.c > @@ -486,8 +486,7 @@ static av_always_inline int > encode_alpha_slice_data(AVCodecContext *avctx, int8_ > run++; > } > } while (idx < num_coeffs); > - if (run) > - put_alpha_run(&pb, run); > + put_alpha_run(&pb, run); > flush_put_bits(&pb); > *a_data_size = put_bytes_output(&pb); > > diff --git a/libavcodec/proresenc_kostya.c b/libavcodec/proresenc_kostya.c > index e904632f8e..8d45e42d1a 100644 > --- a/libavcodec/proresenc_kostya.c > +++ b/libavcodec/proresenc_kostya.c > @@ -562,8 +562,7 @@ static void encode_alpha_plane(ProresContext *ctx, > PutBitContext *pb, > run++; > } > } while (idx < num_coeffs); > - if (run) > - put_alpha_run(pb, run); > + put_alpha_run(pb, run); > }
LGTM, thanks. _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
