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). > >> >> 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. -- regards, Stan [1] https://www.spinics.net/lists/linux-media/msg167794.html
