[FFmpeg-trac] #3147(avcodec:new): H264 - Wrong field order
FFmpeg
trac at avcodec.org
Wed May 7 11:36:53 CEST 2014
#3147: H264 - Wrong field order
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Reporter: Underground78 | Owner:
Type: defect | Status: new
Priority: normal | Component: avcodec
Version: git-master | Resolution:
Keywords: h264 | Blocked By:
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
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Comment (by t.rapp):
I also stumbled over this problem a few weeks ago. From looking at the
source and some small debugging it seems that MediaInfo derives the field
order from the picture "bottom_field_flag":
Recommendation H.264
(https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-H.264-200305-S!!PDF-E&type=items)
page 80:
"""
bottom_field_flag equal to 1 specifies that the slice is part of a coded
bottom field. bottom_field_flag equal to 0 specifies that the picture is
a
coded top field. When this syntax element is not present for the current
slice, it shall be inferred to be equal to 0.
"""
FFmpeg relies only on the information in `h->sei_pic_struct`. When trying
to use `h->picture_structure` I stumble over the issue that FFmpeg
defaults to `h->picture_structure = PICT_FRAME` when the bottom_field_flag
is absent instead of `h->picture_structure = PICT_BOTTOM_FIELD` as
mentioned in the specs. But then I am unsure how to differ between
interlaced and non-interlaced data.
--
Ticket URL: <https://trac.ffmpeg.org/ticket/3147#comment:3>
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