[FFmpeg-devel] [PATCH 1/3] lavf/riffenc: Improve spec compliance

Mats Peterson matsp888 at yahoo.com
Fri Mar 11 18:06:49 CET 2016

On 03/11/2016 06:04 PM, Mats Peterson wrote:
> On 03/11/2016 05:10 AM, Mats Peterson wrote:
>> Forget patch 2/3 and 3/3 from the old patch set.
>>  From the Microsoft documentation for BITMAPINFOHEADER at
>> https://msdn.microsoft.com/en-us/library/windows/desktop/dd318229%28v=vs.85%29.aspx:
>> "biSize: Specifies the number of bytes required by the structure. This
>> value does not include the size of the color table or the size of the
>> color masks, if they are appended to the end of structure."
>> So, biSize is always 40. Also, Windows Media Player won't detect video
>> encoded with Microsoft Video 1 in 8 bpp mode if this value is anything
>> else than 40. I don't know about other codecs, they probably work.
>> Anyway, we should stick with the specs, and not include the palette size
>> in that field.
>> Regarding the biClrUsed field, I'm setting it to 1 <<
>> bits_per_coded_sample if palettized video, since setting it to 0 is
>> another case where it won't work with Windows Media Player and Microsoft
>> Video 1 in 8 bpp mode.
>> Mats
> Regarding HuffYUV, I would say it breaks the specs by using its own
> BITMAPINFOHEADER larger than 40 bytes, but we can't do much about that
> now. For other codecs, anything after the BITMAPINFOHEADER, be it a
> palette or other data, should NOT be included in biSize, since that's
> what Microsoft tells us. They don't mention non-palette data, but that's
> almost implicit.
> Remember, biSize is "The number of bytes required by the structure." I'm
> quoting Microsoft. The structure is the BITMAPINFOHEADER, nothing else.
> Mats

To get the size of any "global non-palette header" or whatever, just 
subtract the size of the BITMAPINFOHEADER (40 bytes) from the size of 
the strf chunk.


Mats Peterson

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