[FFmpeg-devel] [PATCH v2 01/11] avcodec/vvc: add shared header for vvc

[Nuo Mi]

On Tue, Jan 12, 2021 at 6:01 AM Mark Thompson <sw at jkqxz.net> wrote:

> On 10/01/2021 08:35, Nuo Mi wrote:
> > On Sun, Jan 10, 2021 at 9:39 AM Nuo Mi <nuomi2021 at gmail.com> wrote:
> >> On Sun, Jan 10, 2021 at 3:09 AM Mark Thompson <sw at jkqxz.net> wrote:
> >>> On 09/01/2021 07:34, Nuo Mi wrote:
> >>>> ---
> >>>>    libavcodec/vvc.h | 124
> +++++++++++++++++++++++++++++++++++++++++++++++
> >>>>    1 file changed, 124 insertions(+)
> >>>>    create mode 100644 libavcodec/vvc.h
> >>>>
> >>>> diff --git a/libavcodec/vvc.h b/libavcodec/vvc.h
> >>>> new file mode 100644
> >>>> index 0000000000..0bd2acac1d
> >>>> --- /dev/null
> >>>> +++ b/libavcodec/vvc.h
> >>>> @@ -0,0 +1,124 @@
> >>>> ...
> >>>> +
> >>>> +    // A.4.1: the highest level allows a MaxLumaPs of 35 651 584.
> >>>> +    VVC_MAX_LUMA_PS = 35651584,
> >>>> +    // A.4.1: pic_width_in_luma_samples and
> pic_height_in_luma_samples
> >>> are
> >>>> +    // constrained to be not greater than sqrt(MaxLumaPs * 8).  Hence
> >>> height/
> >>>> +    // width are bounded above by sqrt(8 * 35651584) = 16888.2
> samples.
> >>>> +    VVC_MAX_WIDTH  = 16888,
> >>>> +    VVC_MAX_HEIGHT = 16888,
> >>>> +
> >>>> +    // A.4.1: table A.1 allows at most 440 tiles for any au.
> >>>> +    VVC_MAX_TILE_ROWS    = 440,
> >>>
> >>> Is this bound really the best we can do?
> >>>
> >>> That is, is it actually possible to construct a valid stream with 440
> >>> tile rows?  It must have a single tile column and a height of at least
> >>> 14080 (for 440 rows of 32x32 CTUs), which feels extreme enough that it
> >>> might hit some of the other level constraints.
> >>>
> >> The  VVC_MAX_HEIGHT is 16888, it's higher than 14080.
> >> If we limit the VVC_MAX_HEIGHT to 4k, we can reduce it to 135.
>  >
>  > How about we define it as 20,  check the size and return error if > 20.
>  > 20 should enough for most of clips. hevc used 20.
>
> I'm specifically asking whether any of the other limits imply a better
> bound on the number of columns.  Can a 32x14080 stream (or something
> similar) with 440 tiles ever be valid given all of the constraints?
>
> 440 is not large enough that it would matter in terms of space used, so if
> there isn't actually a better implied limit then leave it as 440.  (<1kB -
> constrast that with the entry points, which are already >10kB of
> almost-never-used space with the current limit.)
>
No, I did not see and constraint in spec and the reference code. It does
not needed to be 32x14080, it can be 1920x14080 too.

>
> >>>> +    // A.4.1: table A.1 allows at most 20 tile columns for any level.
> >>>> +    VVC_MAX_TILE_COLUMNS = 20,
> >>>> +
> >>>> +    // A.4.1 table A.1 allows at most 600 slice for any level.
> >>>> +    VVC_MAX_SLICES = 600,
> >>>> ...
>
> - Mark
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