[FFmpeg-devel] [PATCH v2 1/4] lavc/vaapi_encode: add EQUAL_MULTI_ROWS support for slice structure

[Mark Thompson]

On 19/07/2020 08:00, Linjie Fu wrote:
> On Thu, Jun 18, 2020 at 1:36 PM Linjie Fu <linjie.justin.fu at gmail.com> wrote:
>>
>> On Tue, May 12, 2020 at 9:49 PM Linjie Fu <linjie.fu at intel.com> wrote:
>>>
>>> VA_ENC_SLICE_STRUCTURE_EQUAL_MULTI_ROWS is added to in the latest
>>> libva (1.8.0) which matches the hardware behaviour:
>>>
>>> /** \brief Driver supports any number of rows per slice but they must be the same
>>> *       for all slices except for the last one, which must be equal or smaller
>>> *       to the previous slices. */
>>>
>>> And VA_ENC_SLICE_STRUCTURE_EQUAL_ROWS is kind of deprecated for iHD
>>> since it's somehow introduced in [1] however misleading from what we
>>> actually handle, and one row per slice would not get a good quality.
>>>
>>> Caps query support in driver is WIP, and this would fix the multi slice
>>> encoding for VAEntrypointEncSliceLP.
>>>
>>> [1]<https://github.com/intel/libva/commit/0e6d5441f19bdc674b4da3169d614d10fd644778>
>>>
>>> Signed-off-by: Linjie Fu <linjie.fu at intel.com>
>>> ---
>>>   libavcodec/vaapi_encode.c | 3 +++
>>>   1 file changed, 3 insertions(+)
>>>
>>> diff --git a/libavcodec/vaapi_encode.c b/libavcodec/vaapi_encode.c
>>> index cb05ebd..234618a 100644
>>> --- a/libavcodec/vaapi_encode.c
>>> +++ b/libavcodec/vaapi_encode.c
>>> @@ -1888,6 +1888,9 @@ static av_cold int vaapi_encode_init_slice_structure(AVCodecContext *avctx)
>>>           req_slices = avctx->slices;
>>>       }
>>>       if (slice_structure & VA_ENC_SLICE_STRUCTURE_ARBITRARY_ROWS ||
>>> +#if VA_CHECK_VERSION(1, 8, 0)
>>> +        slice_structure & VA_ENC_SLICE_STRUCTURE_EQUAL_MULTI_ROWS ||
>>> +#endif
>>>           slice_structure & VA_ENC_SLICE_STRUCTURE_ARBITRARY_MACROBLOCKS) {
>>>           ctx->nb_slices  = req_slices;
>>>           ctx->slice_size = ctx->slice_block_rows / ctx->nb_slices;
>>> --
>>> 2.7.4
>>
>> Full support is provided in libva[1] and media-driver[2], and we've
>> observed it works for multi slice encoding for AVC. (300+ cases)
>>
>> Prefer to apply this soon with commit message refined.
>>
> Applied, thx.
Treating EQUAL_MULTI_ROWS in the same way as the arbitrary-size cases is just wrong.

Consider 9 rows, 4 slices - we pick 4 slices with sizes { 3, 2, 2, 2 }, which EQUAL_MULTI_ROWS does not allow.

It isn't possible to split the frame into 4 slices at all with the EQUAL_MULTI_ROWS structure - the closest options are 3 slices with sizes { 3, 3, 3 } or 5 slices with sizes { 2, 2, 2, 2, 1 }.

You can see the same problem at 1080p with five slices.

Thanks,

- Mark