Fwd: [Cellar] Depth offsets for subtitles in case of 3D MVC tracks in MKV files

FW answer


---------- Forwarded message ----------
From: Steve Lhomme <[email protected]>
Date: 2016-02-29 9:24 GMT+01:00
Subject: Re: [Matroska-devel] [Cellar] Depth offsets for subtitles in
case of 3D MVC tracks in MKV files
To: Hendrik Leppkes <[email protected]>


2016-02-29 9:17 GMT+01:00 Hendrik Leppkes <[email protected]>:
> On Mon, Feb 29, 2016 at 8:51 AM, Steve Lhomme <[email protected]> wrote:
>>
>> What is the range of depth allowed in Blu-Rays ? Are they discrete
>> value or floating values ?
>>
>
> The "depth" is defined in discrete pixel values in the BD SEI, ie. the
> offset to move it left/right for each eye, so it doesn't have a direct
> meaning of "depth", but just instructions on how to render it.

Ah, interresting. We could still use a z-order value, because that's
what 3D is about. But then it would probably be a float to actually
translate to a wide range of possibilities. But, as seen with the rare
float values in Matroska, in the case where it's actually used (this
case) it would just lead to approximate values of the original format.

> Note that the way this is implemented on Blu-rays, the depth can
> change from frame to frame. Every GOP has a new SEI block which
> includes one offset for every frame in the SEI, so its controlled on a
> frame level, not a scene/GOP level.

So I think we should go with the CodecState approach. Meaning we need
a specific codec ID for such Blu-Ray subtitles. We should not write
the CodecState if the values are the same as the time it was
previously written.

This is also assuming the subtitles are always key frames, so the
(de)coding order is also the display order.

--
Steve Lhomme
Matroska association Chairman


-- 
Steve Lhomme
Matroska association Chairman
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