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

> 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.

Alternatively if the values are expected to change a lot
BlockAdditional could be used. The data are left to interpretation by
the codec, just like CodecState but doesn't require the blocks to be
added to the Seek entries.

https://matroska.org/technical/specs/index.html#BlockAdditional

> 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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