Re: [PATCH v2 0/3] media: uapi: h264: First batch of adjusments

[Boris Brezillon <boris.brezillon@collabora.com>]

On Mon, 10 Jun 2019 10:52:47 +0200
Boris Brezillon <boris.brezillon@collabora.com> wrote:

> Hello,
> 
> This is a first batch of adjustments to the stateless H264 decoder
> uAPI. The first one is about adding support for per-frame decoding,
> which is the only mode supported on some codecs (the hantro G1 block
> supports per-slice decoding but not in an way that would allow
> efficient multiplexing of several decoding contexts).
> 
> The second modification drops the P0/B0/B1 ref lists from the
> decode_params control. These lists are no longer needed now that we know
> we can build them kernel side based on the DPB.
> 
> There are few more changes in the pipe, but I'd like to sync with Paul,
> Jonas, Jernej and Nicolas before modifying:
> * Enforce order of the scaling list (looks like the rockchip and cedrus
>   have different expectations)
> * Pass top/bottom field info as flags in the DPB entry: the field
>   attached to the capture buffer is not accurate as capture bufs might
>   contain both top/bottom (meaning they are actually interlaced), but a
>   coded frame might contain only one of these fields. Note
>   that there's also a problem with the output -> capture field flag
>   propagation we have in copy_metadata() because a coded slice might
>   contain only data for top or bottom, but the capture frame might
>   contain both. Doing capture->field = output->field means we're lying
>   about what's inside the capture buffer (not sure we have
>   implementation checking that)
> * s/dpb/refs/: looks like we're abusing the term DPB which is supposed
>   to be implementation specific. What's provided by the bitstream is a
>   list of references that will be used to decode a frame
> * ... (add your own)
> 
> Feel free to comment on these changes and/or propose alternatives.
> 
> Regards,
> 
> Boris
> 
> Changes in v2:
> * Allow decoding multiple slices in per-slice decoding mode
> * Minor doc improvements/fixes

Forgot:

* Drop sunxi changes until we settle on the uAPI changes (supporting
  multi-slice decoding in per-slice mode requires a bit more work and I
  can't test it)

> 
> Boris Brezillon (3):
>   media: uapi: h264: Clarify our expectations regarding NAL header
>     format
>   media: uapi: h264: Add the concept of decoding mode
>   media: uapi: h264: Get rid of the p0/b0/b1 ref-lists
> 
>  .../media/uapi/v4l/ext-ctrls-codec.rst        | 56 +++++++++++++++----
>  drivers/media/v4l2-core/v4l2-ctrls.c          |  9 +++
>  include/media/h264-ctrls.h                    | 13 +++++
>  3 files changed, 68 insertions(+), 10 deletions(-)
>