On Fri, Jan 25, 2019 at 10:04 PM Paul Kocialkowski <paul.kocialkowski@xxxxxxxxxxx> wrote: > > Hi, > > On Thu, 2019-01-24 at 20:23 +0800, Ayaka wrote: > > > > Sent from my iPad > > > > > On Jan 24, 2019, at 6:27 PM, Paul Kocialkowski <paul.kocialkowski@xxxxxxxxxxx> wrote: > > > > > > Hi, > > > > > > > On Thu, 2019-01-10 at 21:32 +0800, ayaka wrote: > > > > I forget a important thing, for the rkvdec and rk hevc decoder, it would > > > > requests cabac table, scaling list, picture parameter set and reference > > > > picture storing in one or various of DMA buffers. I am not talking about > > > > the data been parsed, the decoder would requests a raw data. > > > > > > > > For the pps and rps, it is possible to reuse the slice header, just let > > > > the decoder know the offset from the bitstream bufer, I would suggest to > > > > add three properties(with sps) for them. But I think we need a method to > > > > mark a OUTPUT side buffer for those aux data. > > > > > > I'm quite confused about the hardware implementation then. From what > > > you're saying, it seems that it takes the raw bitstream elements rather > > > than parsed elements. Is it really a stateless implementation? > > > > > > The stateless implementation was designed with the idea that only the > > > raw slice data should be passed in bitstream form to the decoder. For > > > H.264, it seems that some decoders also need the slice header in raw > > > bitstream form (because they take the full slice NAL unit), see the > > > discussions in this thread: > > > media: docs-rst: Document m2m stateless video decoder interface > > > > Stateless just mean it won’t track the previous result, but I don’t > > think you can define what a date the hardware would need. Even you > > just build a dpb for the decoder, it is still stateless, but parsing > > less or more data from the bitstream doesn’t stop a decoder become a > > stateless decoder. > > Yes fair enough, the format in which the hardware decoder takes the > bitstream parameters does not make it stateless or stateful per-se. > It's just that stateless decoders should have no particular reason for > parsing the bitstream on their own since the hardware can be designed > with registers for each relevant bitstream element to configure the > decoding pipeline. That's how GPU-based decoder implementations are > implemented (VAAPI/VDPAU/NVDEC, etc). > > So the format we have agreed on so far for the stateless interface is > to pass parsed elements via v4l2 control structures. > > If the hardware can only work by parsing the bitstream itself, I'm not > sure what the best solution would be. Reconstructing the bitstream in > the kernel is a pretty bad option, but so is parsing in the kernel or > having the data both in parsed and raw forms. Do you see another > possibility? Is reconstructing the bitstream so bad? The v4l2 controls provide a generic interface to an encoded format which the driver needs to convert into a sequence that the hardware can understand. Typically this is done by populating hardware-specific structures. Can't we consider that in this specific instance, the hardware-specific structure just happens to be identical to the original bitstream format? I agree that this is not strictly optimal for that particular hardware, but such is the cost of abstractions, and in this specific case I don't believe the cost would be particularly high?
