lkml.org 
[lkml]   [2020]   [Jun]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] v4l2-ctrl: add control for thumnails
From
Date
Hi Hans,

On 6/4/20 12:08 PM, Hans Verkuil wrote:
> 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@linaro.org>
>>>>> ---
>>>>> 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.

Yes, it is.
To me V4L2_CID_MPEG_VIDEO_DECODE_SYNC_FRAMES sounds better. If you are
fine I can send a new patch.

The definition of "sync frames" is a bit difficult for codec-agnostic
controls. Is it sound better "INTRA", DECODE_INTRA_FRAMES (ONLY)?

>
> 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.
>>
>

--
regards,
Stan

\
 
 \ /
  Last update: 2020-06-04 14:35    [W:0.080 / U:0.892 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site