I would like to clarify the value of VAConfigAttribEncMaxRefFrames.
Below is the document about it.
> Maximum number of reference frames. Read-only.
> This attribute determines the maximum number of reference
> frames supported for encoding.
> Note: for H.264 encoding, the value represents the maximum number
> of reference frames for both the reference picture list 0 (bottom
> 16 bits) and the reference picture list 1 (top 16 bits).
It looks like it reports the maximum number of reference frames that
can be "actually" used for encoding. (1)
So I expect, if value=1 is reported, a single frame out of the picture
list can be used.
On the other hand, there is no API to know the maximum picture lists.
The size of each of the picture lists can be up to 16 in H264.
Must a VA-API driver support up to 16 in H264?
Aside, in H264, a bit confusingly,max_num_ref_frames in SPS is the
maximum length of sum of picture lists.
Perhaps, does the VAConfigAttribEncMaxRefFrames report it. (2)
Which is correct, (1) or (2)?