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

[Mark Thompson]

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.)

>>>> +    // 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