Re: [Cellar] FFV1 Version 4

[Jerome Martinez <[e-mail]>]

Le 05/01/2016 18:44, Michael Niedermayer a écrit :
> the global header / extradata / ConfigurationRecord can and should be 
> duplicated at the container level. repeating it at the codec level 
> would make finding a duplicate element relativly hard as one probably 
> would have to scan the whole file. A container could contain something 
> like an index to point to redundant copies, while at codec level this 
> would not work so easily 

As far as I know, I never seen duplicated ConfigurationRecord.
I guess we should add such option (e.g. in Matroska specs, there is 
already a discussion about duplicated parts) for people wanting to 
secure this important part.5

> [...]
>
> different picture_structures in 1 frame dont make sense or do i
> misunderstand ?

Some people may be crazy enough for wanting and trying e.g.:
- slice 0,0 top field first
- slice 0,0 (the same as the line above) bottom field first
- slice 0,1 progressive
- slice 1,0 bottom field first
- slice 1,0 (the same as the line above) top field first
- slice 1,1 progressive
(we have MABFF feature in AVC/H264, so I don't invent too much)

and for the moment, I see nothing in the FFV1 specification forbidding 
that (did I miss something?)
So either we are clear it is authorized (and the reference decoder can 
deal with it), or we explicitly forbid it (picture_structure is same in 
all slices of a frame)


>
>> Additionally, picture_structure, sar_num, sar_dem (and other?) do
>> not use to change (or they change as often as  chroma_planes,
>> h_chroma_subsample, alpha_plane...), so we may consider to put them
>> in the ConfigurationRecord() too (and we may need to take care of
>> duplicating it in the container?)
> they could optionally be put in the global ConfigurationRecord
> but it should stay possible for them to change if thats what the
> source video we encode is doing

I like the idea to have such optional possibility. this is not a lot, 
but always some bits of compression.
A candidate for FFV1 version 4 feature!

Jérôme