On 14-07-2020 05:14 pm, Andreas Rheinhardt wrote:
Gyan Doshi:
Some legacy applications such as AVI2MVE expect raw RGB bitmaps
to be stored bottom-up, whereas our RIFF BITMAPINFOHEADER assumes
they are always stored top-down and thus write a negative value
for height. This can prevent reading of these files.
Option flipped_raw_rgb added to AVI and Matroska muxers
which will write positive value for height when enabled.
Note that the user has to flip the bitmaps beforehand using other
means such as the vflip filter.
---
1. The avi demuxer adds "BottomUp" to the extradata in case it demuxes
bottom up data. The Matroska demuxer currently doesn't and so rawvideo
stored in Matroska in vfw mode will always be treated as top-down. This
needs to be fixed, too.
Agreed. But that's a separate patch,
2. But why don't we add an option to the raw encoder so that it adds (or
maybe switches?) "BottomUp" to the extradata to indicate that the output
is bottom-up? That seems like a better place for me. (E.g. it would
naturally allow to set the bottom-up/top-down property on a per-stream
basis.)
This "feature" is a quirk of Microsoft / RIFF containers (or their
accommodation in other containers viz. VFW in Matroska) rather than a
generic property of raw video streams - the extradata string is an
ffmpeg invention. Since this option is meant to pacify old legacy apps
which wouldn't deal with multiple streams, per-stream assignment is a
bonus but not necessary. I modified Matroska muxer for completeness
rather than expecting anyone to actually use it.
Gyan
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