This is really just a matter of choice. If you don't care about spec-conformance in this particular case, top_field_first *could* be 1 and/or picture_structure *could* be not 3 even when progressive_sequence is 1, so which one do you choose to believe? The truth is, it doesn't even matter.
If you insist on making it more clumsy and silly, I can resend. On Sun, 6 Feb 2022 at 13:46, Andreas Rheinhardt <andreas.rheinha...@outlook.com> wrote: > > Tom Yan: > > the top_field_first bit is only used to indicate the field order > > when the picture is a frame picture (which consists of two fields) > > but not when it is a field picture (which consists of one single > > top or bottom field). > > > > also removing the unnecessary progressive_sequence check (the bit > > is mandated to be 0 if progressive_frame is 0 on any picture in the > > sequence). > > > > Just because something is mandated does not mean that it is so; > spec-incompliant files exist. > > > Signed-off-by: Tom Yan <tom.t...@gmail.com> > > --- > > libavcodec/mpegvideo_parser.c | 15 +++++++++------ > > 1 file changed, 9 insertions(+), 6 deletions(-) > > > > diff --git a/libavcodec/mpegvideo_parser.c b/libavcodec/mpegvideo_parser.c > > index c5dc867d24..004ff602f6 100644 > > --- a/libavcodec/mpegvideo_parser.c > > +++ b/libavcodec/mpegvideo_parser.c > > @@ -181,6 +181,7 @@ static void > > mpegvideo_extract_headers(AVCodecParserContext *s, > > break; > > case 0x8: /* picture coding extension */ > > if (bytes_left >= 5) { > > + s->picture_structure = buf[2] & 0x3; > > top_field_first = buf[3] & (1 << 7); > > repeat_first_field = buf[3] & (1 << 1); > > progressive_frame = buf[4] & (1 << 7); > > @@ -198,13 +199,15 @@ static void > > mpegvideo_extract_headers(AVCodecParserContext *s, > > } > > } > > > > - if (!pc->progressive_sequence && > > !progressive_frame) { > > - if (top_field_first) > > - s->field_order = AV_FIELD_TT; > > - else > > - s->field_order = AV_FIELD_BB; > > - } else > > + if (progressive_frame) > > s->field_order = AV_FIELD_PROGRESSIVE; > > + else if (top_field_first || > > + /* top_field_first is mandated to be 0 > > when > > + the picture is not a frame picture) */ > > + s->picture_structure == > > AV_PICTURE_STRUCTURE_TOP_FIELD) > > + s->field_order = AV_FIELD_TT; > > + else > > + s->field_order = AV_FIELD_BB; > > } > > break; > > } > > _______________________________________________ > 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". _______________________________________________ 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".