[Matroska-devel] New Matroska field: chroma range/pixel format

Dave Rice dave at dericed.com
Wed Sep 23 21:33:03 CEST 2015


> On Sep 23, 2015, at 3:27 PM, wm4 <nfxjfg at googlemail.com> wrote:
> 
> On Wed, 23 Sep 2015 18:00:58 +0200
> Steve Lhomme <slhomme at matroska.org> wrote:
> 
>> We currently have a ColourSpace field that is just mapped from AVI.
>> I'm not even sure it's used.
> 
> Raw video. Might be FFmpeg specific.

When the codec id is V_Uncompressed, the ColourSpace shows the fourcc of the uncompressed data, example: YUY2 or UYVY (from AVI fourccs). Without this uncompressed in Matroska wouldn't be characterized with any sample ordering, chroma subsampling or bit depth as inferred by the fourcc in ColourSpace.

>> When storing raw video, the pixels are stored in a certain way and
>> decoding the pixels need some conversion from this encoding to
>> whatever your screen is using. Right now we don't have all the fields
>> needed to describe these raw data.

Right, even if uncompressed video is stored in Matroska, there is no method to describe it as full range or broadcast range or whether to use bt601, bt709, etc.
dave

>> It may also be useful to tell easily if a H264 or VP9 video is in 8
>> bits per pixels, 10 or 12 bits, without having to inspect codec
>> private data or even Blocks.
>> 
>> I think a field for Chroma Subsampling (I420, I422, Y410, etc) and one
>> for Chroma Range (BT.608, BT.709, BT.2020) should be sufficient. The
>> Chroma Subsampling generally described how each "plane" is layed out
>> in the raw data.
> 
> That kind of redundant info just seems to make everything harder than
> it is...
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