avformat/riffenc: indicate storage of flipped RGB bitmaps

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 files changed, 13 insertions, 0 deletions

diff --git a/doc/muxers.texi b/doc/muxers.texi
index 86976f4f61..813b4678f4 100644
--- a/doc/muxers.texi
+++ b/doc/muxers.texi
@@ -89,6 +89,12 @@ specific scenarios, e.g. when merging multiple audio streams into one for
 compatibility with software that only supports a single audio stream in AVI
 (see @ref{amerge,,the "amerge" section in the ffmpeg-filters manual,ffmpeg-filters}).
 
+@item flipped_raw_rgb
+If set to true, store positive height for raw RGB bitmaps, which indicates
+bitmap is stored bottom-up. Note that this option does not flip the bitmap
+which has to be done manually beforehand, e.g. by using the vflip filter.
+Default is @var{false} and indicates bitmap is stored top down.
+
 @end table
 
 @anchor{chromaprint}
@@ -1413,6 +1419,13 @@ disposition default exists, no subtitle track will be marked as default.
 In this mode the FlagDefault is set if and only if the AV_DISPOSITION_DEFAULT
 flag is set in the disposition of the corresponding stream.
 @end table
+
+@item flipped_raw_rgb
+If set to true, store positive height for raw RGB bitmaps, which indicates
+bitmap is stored bottom-up. Note that this option does not flip the bitmap
+which has to be done manually beforehand, e.g. by using the vflip filter.
+Default is @var{false} and indicates bitmap is stored top down.
+
 @end table
 
 @anchor{md5}