[FFmpeg-devel] [PATCH] lavc/vaapi_encode: Don't pass VAConfigAttribEncPackedHeaders with value set to 0

[Eoff, Ullysses A]

> -----Original Message-----
> From: ffmpeg-devel [mailto:ffmpeg-devel-bounces at ffmpeg.org] On Behalf Of Mark Thompson
> Sent: Tuesday, February 13, 2018 11:54 AM
> To: FFmpeg development discussions and patches <ffmpeg-devel at ffmpeg.org>
> Subject: Re: [FFmpeg-devel] [PATCH] lavc/vaapi_encode: Don't pass VAConfigAttribEncPackedHeaders with value set to 0
> 
> On 13/02/18 18:52, Mark Thompson wrote:
> > On 13/02/18 08:24, Haihao Xiang wrote:
> >> Recent Intel i965 driver commit strictly disallows application to set
> >> unsupported attribute values, VA_ENC_PACKED_HEADER_NONE (0) is not used
> >> in Intel i965 driver, so application shouldn't pass this value to the
> >> driver. On the other hand, VA_ENC_PACKED_HEADER_NONE (0) means the
> >> driver doesn't support any packed header mode, so application also
> >> shouldn't pass packed header to driver if a driver returns
> >> VA_ENC_PACKED_HEADER_NONE (0), the driver should work without
> >> VAConfigAttribEncPackedHeaders set for this case.
> >>
> >> In addition, VA_ATTRIB_NOT_SUPPORTED and VA_ENC_PACKED_HEADER_NONE make
> >> thing messy, we will deprecate VA_ENC_PACKED_HEADER_NONE in the
> >> future. See https://github.com/intel/libva/issues/178 for more information.
> >>
> >> This fixes broken vp9 encoder on Kably Lake with Intel I965 driver.
> >>
> >> Signed-off-by: Haihao Xiang <haihao.xiang at intel.com>
> >> ---
> >>  libavcodec/vaapi_encode.c | 4 ++++
> >>  1 file changed, 4 insertions(+)
> >>
> >> diff --git a/libavcodec/vaapi_encode.c b/libavcodec/vaapi_encode.c
> >> index e371f5761ee..1d30aabed40 100644
> >> --- a/libavcodec/vaapi_encode.c
> >> +++ b/libavcodec/vaapi_encode.c
> >> @@ -1111,6 +1111,10 @@ static av_cold int vaapi_encode_config_attributes(AVCodecContext *avctx)
> >>                         ctx->va_packed_headers, attr[i].value);
> >>                  ctx->va_packed_headers &= attr[i].value;
> >>              }
> >> +
> >> +            if (!ctx->va_packed_headers)
> >> +                continue;
> >> +
> >>              ctx->config_attributes[ctx->nb_config_attributes++] =
> >>                  (VAConfigAttrib) {
> >>                  .type  = VAConfigAttribEncPackedHeaders,
> >>
> >
> > This seems wrong to me: the driver has indicated that packed headers are supported, so the user is providing this attribute to
> indicate to the driver that they will not use any of them.  Compare the VP8 case, where the driver does not support them and says so -
> there we correctly don't provide the attribute (though maybe the commentary could be clearer on that).
> 
> Right, I hadn't realised you had already made a change so that encoding is currently broken.  I've made
> <https://github.com/intel/intel-vaapi-driver/pull/358> to revert the API/ABI-breaking part of the change.
> 
> Thanks,
> 
> - Mark

I prefer this patch over the one for intel-vaapi-driver.

The va.h documentation for VA_ENC_PACKED_HEADER_NONE
says "Driver does not support any packed headers mode".
Hence, it's only valid for reporting to client that packed headers
are "unsupported".  Unfortunately, VA_ENC_PACKED_HEADER_NONE 
is redundant/ambiguous since there is also
VA_ATTRIB_NOT_SUPPORTED to relay the same information.
This is why we want to deprecate VA_ENC_PACKED_HEADER_NONE
in VAAPI.

I don't think it's correct for clients to send
VA_ENC_PACKED_HEADER_NONE attribute value to the driver
when the driver reports packed headers are "supported".  It
goes against VA_ENC_PACKED_HEADER_NONE's documented
purpose.  AFAIK, libavcodec is the only library that does this.  It
is better to just omit the attribute altogether if client does not
want to use any of the "supported" packed headers.  And this
patch solves that.

In the future, it's probably worth amending VAAPI to allow for
drivers to relay when packed headers are required vs. optional,
too.

U. Artie

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