[FFmpeg-devel] PATCH] lavf/qtpalette: Ignore greyscale bit in certain cases

Mats Peterson matsp888 at yahoo.com
Sat Jan 2 06:39:03 CET 2016

The QuickTime File Format Specification states the following:

"Depth: A 16-bit integer that indicates the pixel depth of the
compressed image. Values of 1, 2, 4, 8 ,16, 24, and 32 indicate the
depth of color images. The value 32 should be used only if the image
contains an alpha channel. Values of 34, 36, and 40 indicate 2-, 4-, and
8-bit grayscale, respectively, for grayscale images."

There is no mention of value 33, i.e. 1-bit video (0x01) with the
greyscale bit (0x20) set. I therefore suggest that we ignore the
greyscale bit when processing 1-bit video. Another reason to do this is
that the first 1-bit sample file below will be displayed properly with
blue colors in QuickTime in Windows or Mac *in spite of* the greyscale
bit being set.

Also, QuickTime in Windows or Mac ignores the greyscale bit if the
video sample description contains a palette, regardless of bit depth.
This is undocumented behaviour, but I think we should do the same, and
it seems pretty logical after all, since one wouldn't really bother
putting a customized palette into a grayscale file anyway. See the
second 8-bit sample file below, which has the greyscale bit set, and
which contains a palette in the video sample description. In Windows or
Mac, it will be displayed with the palette in the sample description, in
spite of the greyscale bit being set.


Mats Peterson
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