Re: [PATCH v2 1/4] media: v4l2-ctrls: Add intra-refresh period control

[Stanimir Varbanov]

On 1/12/21 12:05 PM, Hans Verkuil wrote:
> On 06/12/2020 11:27, Stanimir Varbanov wrote:
>> Add a control to set intra-refresh period.
>>
>> Signed-off-by: Stanimir Varbanov <stanimir.varbanov@xxxxxxxxxx>
>> ---
>>  .../userspace-api/media/v4l/ext-ctrls-codec.rst       | 11 +++++++++++
>>  drivers/media/v4l2-core/v4l2-ctrls.c                  |  2 ++
>>  include/uapi/linux/v4l2-controls.h                    |  1 +
>>  3 files changed, 14 insertions(+)
>>
>> diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
>> index 454ecd9a0f83..d65d7c1381b7 100644
>> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
>> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
>> @@ -1104,6 +1104,17 @@ enum v4l2_mpeg_video_h264_entropy_mode -
>>      macroblocks is refreshed until the cycle completes and starts from
>>      the top of the frame. Applicable to H264, H263 and MPEG4 encoder.
>>  
>> +``V4L2_CID_MPEG_VIDEO_INTRA_REFRESH_PERIOD (integer)``
>> +    Intra macroblock refresh period. This sets the period to refresh
>> +    the whole frame. With other words, this defines the number of frames
> 
> With -> In
> 
>> +    for which the whole frame will be intra-refreshed.  An example:
>> +    setting period to 1 means that the whole frame will be refreshed,
>> +    setting period to 2 means that the half of macroblocks will be
>> +    intra-refreshed on frameX and the other half of macroblocks
>> +    will be refreshed in frameX + 1 and so on. Setting period to zero
>> +    means no period is specified.
>> +    Applicable to H264 and HEVC encoders.
> 
> I'm confused. Isn't this the same as V4L2_CID_MPEG_VIDEO_CYCLIC_INTRA_REFRESH_MB?
> Except that here you don't give the number of macroblocks but instead the number
> of frames it will take to fully refresh a frame and leave it to the driver to
> calculate the number of macroblocks?

Yes, correct. The periodic control looks more generic because it doesn't
limit the type of intra-refresh (cyclic vs random vs adaptive) but
instead set the number of frames to fully refresh the whole frame and is
also taken from Android mediacodec [1], where the user doesn't care too
much what intra-refresh type will be used but instead how much frames
are needed to fully refresh.

> 
> If I am right, then you need to clearly document the relationship between the
> two controls, and what happens if you set them both.

Yep, I can add such description.

One note here; the CYCLIC_INTRA_REFRESH_MB and INTRA_REFRESH_PERIOD are
not interchangeable because intra-refresh period could use different
type of inter-refresh, eg. random vs cyclic.

> 
> It seems the venus driver already supports V4L2_CID_MPEG_VIDEO_CYCLIC_INTRA_REFRESH_MB,
> so why add this control as well?

The cyclic intra-refresh control in Venus driver is just enumerable but
ignored when set, in other words it does nothing.

> 
> Regards,
> 
> 	Hans
> 

[1]
https://developer.android.com/reference/android/media/MediaFormat#KEY_INTRA_REFRESH_PERIOD

-- 
regards,
Stan