[vlc-devel] [PATCH 3/7] video_format: add a interlaced flag in the video format

[Steve Lhomme]

On 2020-11-07 12:59, Rémi Denis-Courmont wrote:
> Not that I'd personally know why it currently is the way it is.
> 
> Would this patchset allow getting the deinterlacing status from V4L and 
> equivalent? In other words, how does it work for demuxers, especially 
> raw video demuxers?

I have no idea how V4L works and even less how it handles interlacing. 
So I don't know.

> Le 6 novembre 2020 19:02:18 GMT+02:00, "Rémi Denis-Courmont" 
> <remi at remlab.net> a écrit :
> 
>     Le perjantaina 6. marraskuuta 2020, 16.42.10 EET Steve Lhomme a écrit :
> 
>         So we can catch format differences to detect interlace mode
>         changes in push
>         mode.
> 
> 
>     AFAIU, that's a big no-no for some muxers / codecs - which is why it is the
>     way it currently is.

It is currently designed for a pull system. This existing code doesn't 
even deinterlace the first interlaced frame. So I don't think the 
current design should tell us how it should be done in pull model.

The interlacing is already a "state" of the whole pipeline. It's 
currently detected from decoded pictures. In the past it was not 
possible to request on a new format on the output without losing 
everything that was pushed before. Now we can change the pipeline format 
and keep everything that was there before. So it's not possible to set 
the interlacing state when it changes in the source. That would be 
coherent with how push work for all the other "states". Or, the other 
way around, I don't see why interlacing should be a special case.