On 04/06/2020 11:02, Stanimir Varbanov wrote: > Hi Hans, > > On 5/27/20 12:53 AM, Stanimir Varbanov wrote: >> Hi Hans, >> >> On 5/26/20 3:04 PM, Hans Verkuil wrote: >>> On 26/05/2020 10:54, Stanimir Varbanov wrote: >>>> Add v4l2 control for decoder thumbnail. >>>> >>>> Signed-off-by: Stanimir Varbanov <stanimir.varbanov@xxxxxxxxxx> >>>> --- >>>> Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst | 7 +++++++ >>>> drivers/media/v4l2-core/v4l2-ctrls.c | 2 ++ >>>> include/uapi/linux/v4l2-controls.h | 2 ++ >>>> 3 files changed, 11 insertions(+) >>>> >>>> diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst >>>> index d0d506a444b1..e838e410651b 100644 >>>> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst >>>> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst >>>> @@ -3726,6 +3726,13 @@ enum v4l2_mpeg_video_hevc_size_of_length_field - >>>> disables generating SPS and PPS at every IDR. Setting it to one enables >>>> generating SPS and PPS at every IDR. >>>> >>>> +``V4L2_CID_MPEG_VIDEO_DECODER_THUMBNAIL (button)`` >>>> + Instructs the decoder to produce immediate output. The decoder should >>>> + consume first input buffer for progressive stream (or first two buffers >>>> + for interlace). Decoder should not allocate more output buffers that it >>>> + is required to consume one input frame. Usually the decoder input >>>> + buffers will contain only I/IDR frames but it is not mandatory. >>> >>> This is very vague. It doesn't explain why the control is called 'THUMBNAIL', >>> but more importantly it doesn't explain how this relates to normal decoding. >> >> If in the normal decode the capture queue buffers are 5, in the >> thumbnail mode the number of buffers will be only 1 (if the bitstream is >> progressive) and this will guarantee low memory usage. The other >> difference is that the decoder will produce decoded frames (without >> errors) only for I/IDR (sync frames). Isn't this really a "DECODE_SYNC_FRAMES_ONLY" control? That's what it does, right? Skip any B/P frames and only decode sync frames. That this is useful for creating thumbnails is just a specific use-case. Regards, Hans >> >>> >>> I.e. if you are decoding and 'press' this control, what happens then? >> >> Might be the button type wasn't great idea. In fact the control should >> be set before streamon so that the driver returns min_capture_bufs 1. >> >>> >>> What exactly is the use-case? >> >> It could be used to generate thumbnails of all video clips in a folder >> or when you open a Gallery application on your phone. >> > > What is your opinion on that control? I could consider to make it Venus > custom control but from the use-case it looks other drivers also can > benefit of it. > > I tried to make more generic one [1] but it looks it will be too difficult. >
