[Libva] (H264) Reference Picture selection

[Sreerenj]

On 14.05.2014 10:51, Xiang, Haihao wrote:
> On Mon, 2014-05-12 at 07:34 +0200, Gwenole Beauchesne wrote:
>> 2014-05-12 7:29 GMT+02:00 Zhao, Yakui <yakui.zhao at intel.com>:
>>> On Sun, 2014-05-11 at 22:41 -0600, Gwenole Beauchesne wrote:
>>>> Hi,
>>>>
>>>> 2014-05-12 3:34 GMT+02:00 Zhao Yakui <yakui.zhao at intel.com>:
>>>>> On Fri, 2014-05-09 at 03:06 -0600, Yuan, Feng wrote:
>>>>>> Hi,
>>>>>>
>>>>>>>>> I have a scheme where the decoder ack's received frames - With this
>>>>>>>>> information I could resync without an IDR by carefully selecting the
>>>>>>>>> reference frame(s).
>>>>>>>> Will you please describe your idea in detail?
>>>>>>>>> long term references would typically be employed as well, but it
>>>>>>>>> seems ref-pic-marking was removed may'13?
>>>>>>>> Why do you hope to use the long-term reference? As you know, the
>>>>>>>> current encoding is based on hardware-acceleration. When more the
>>>>>>>> reference frames can be selected, the driver will be more complex and
>>>>>>>> then the encoding speed is also affected.
>>>>>>> It's for implementing Cisco's clearpath technology
>>>>>>> (http://www.cisco.com/c/dam/en/us/td/docs/telepresence/endpoint/softwa
>>>>>>> re/clearpath/clearpath_whitepaper.pdf)
>>>>>>> Basically one would  periodically mark a P frame as long term reference, in
>>>>>>> case of packet loss one can thus refer to this one instead of restarting the
>>>>>>> stream with an idr.
>>>>>>>
>>>>>>>
>>>>>>> I'm not too concerned about the encoding speed as long as it's above
>>>>>>> realtime (60fps 1920x1080)
>>>>>> Maybe it's more convenient If libva can have a switch for slice_header made between driver and app. Then some specially cases(ref-reorder, long-term-ref) may let app to manage slice-header.
>>>>> Thanks for your suggestion. If the slice-header info is also generated
>>>>> by the app and then be passed to the driver, it can be easy to do the
>>>>> operation of "re-order and long-term-ref"
>>>>>
>>>>> But this will depend on the policy how the slice header info is
>>>>> generated. (by app or the driver). Now this is exported by querying the
>>>>> capability of the driver. If we move this into the app, the
>>>>> infrastructure will be changed a lot.
>>>> Infrastructure of what? The application? No, it doesn't really change
>>>> anything but generating the extra packed slice header.
>>> Currently the app will query the capability of encoding and determine
>>> which kind of header should be passed by the upper application(For
>>> example: PPS/SPS).
>>> If the Slice_header info is exposed, the driver will assume that it is
>>> the responsibility of generating the slice header info. In such case it
>>> is difficult to mix the two working modes without a lot of changes.(One
>>> is that the driver generates the slice header info. Another is that the
>>> app generates the slice header info).
>> Then the driver needs to be fixed to not assume anything. The API and
>> operation points look clear enough, aren't they?
>>
>> The changes to the codec layer are minimal, and this was done already,
>> in multiple instances of codec layers, and with another driver.
> Where is your code for codec layer with packed slice header/packed raw
> data, I want to know the point where is packed slice header / packed raw
> data inserted into the bitstream in the codec layer.
I have these patches for the codec-layer (gstreaemr-vaapi)  but not yet 
integrated to gstreamer-vaapi master.
Submitting all packed_headers in the following order  just after the 
submission of VAEncSequenceParameterBuffer to vaRenderPicture() : 
"packed_sps, packed_pps, packed_slice".
And then submitting Miscparam, PictureParam and SliceParam. Is it not 
enough?

Anyway the intel driver seems to be using fixed size arrays for 
referencing packed headers (packed_header_param[4] and 
packed_header_data[4]) which needs to be changed if there are
multiple slices per frame since we have to submit packed headers for 
each slice. isn't it?


>
>>
>>>>> Another problem is that it is possible that one frame has multiple
>>>>> slices. In such case the user should pass the multiple slice header
>>>>> info.
>>>> This is not an an issue. The API mandates that the packed headers are
>>>> provided in order.
>>>
>>>
>>>> Regards,
>>>> Gwenole.
>>>
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>
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-- 
Thanks
Sree

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