[VAAPI AV1 Encode] Encoder doesn't check VAConfigAttribEncMaxRefFrames

On official ffmpeg (with the upstreamed AV1 encode patch), the encoder seems to be generating bitstreams using always 2 reference frames set to LAST/GOLDEN for P, even when VAConfigAttribEncMaxRefFrames.L0 reports a lower limit (e.g max 1 L0 reference frame).

@feiwan1 Is this something that could be checked so only the LAST reference is used for P when VAConfigAttribEncMaxRefFrames.L0 = 1 ? This affects the vaon12 VA driver which has encode AV1 support over different hardware abstracted through D3D12 reporting different support for VAConfigAttribEncMaxRefFrames.

Thanks!

Actually, looks like this also affects other codecs like H264/HEVC encoding with VAAPI, could we add such check for those as well?

OK, I will add the max ref frames check. BTW, 2 refs for P frame is only avaliable for AV1. Other codecs still use one ref for P frame.

Thanks @feiwan1 ! For B frames in AV1, vaon12 is also reporting the L1 limit in the upper 16 bits of VAConfigAttribEncMaxRefFrames, right now looks like encoding B uses 2 references, could also the max references check be staged in the B case in case in the future there are more references used in B frame, so they're always under the L1 limit of VAConfigAttribEncMaxRefFrames too ?

Thanks @feiwan1 ! For B frames in AV1, vaon12 is also reporting the L1 limit in the upper 16 bits of VAConfigAttribEncMaxRefFrames, right now looks like encoding B uses 2 references, could also the max references check be staged in the B case in case in the future there are more references used in B frame, so they're always under the L1 limit of VAConfigAttribEncMaxRefFrames too ?

Sure, both L0 and L1 should be checked.