[FFmpeg-cvslog] avcodec/mpegvideo_enc: Allow slices only for slice-thread-able codecs

[Andreas Rheinhardt]

ffmpeg | branch: master | Andreas Rheinhardt <andreas.rheinhardt at outlook.com> | Sat Jan 29 22:39:15 2022 +0100| [8ca4b515e73079cda068e253853654db394b8171] | committer: Andreas Rheinhardt

avcodec/mpegvideo_enc: Allow slices only for slice-thread-able codecs

One can use slices without slice-threading. The results for
mpegvideo-encoders are abysmal: AMV, SpeedHQ, H.263, RV10, RV20,
MSMPEG4v2, MSMPEG4v3 and WMV1 produce broken files.
WMV2 meanwhile expects the MpegEncContext given to ff_wmv2_encode_mb()
to be at the beginning of a Wmv2Context (a structure that this encoder
shares with the WMV2 decoder), yet this is only true for the
main context and not for the slice contexts, leading to segfaults.
SpeedHQ additionally triggers an av_assert2, because it is not
byte-aligned at a position where it ought to be byte-aligned.

Given that no codec not supporting slice threading works this commit
disallows using slices unless the encoder supports slice threading.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at outlook.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=8ca4b515e73079cda068e253853654db394b8171
---

 libavcodec/mpegvideo_enc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavcodec/mpegvideo_enc.c b/libavcodec/mpegvideo_enc.c
index 71c999fab0..5abd463430 100644
--- a/libavcodec/mpegvideo_enc.c
+++ b/libavcodec/mpegvideo_enc.c
@@ -603,7 +603,7 @@ av_cold int ff_mpv_encode_init(AVCodecContext *avctx)
     }
 
     if (avctx->slices > 1 &&
-        (avctx->codec_id == AV_CODEC_ID_FLV1 || avctx->codec_id == AV_CODEC_ID_H261)) {
+        !(avctx->codec->capabilities & AV_CODEC_CAP_SLICE_THREADS)) {
         av_log(avctx, AV_LOG_ERROR, "Multiple slices are not supported by this codec\n");
         return AVERROR(EINVAL);
     }