From: Hans Verkuil <hverkuil-cisco@xs4all.nl>
To: Stanimir Varbanov <stanimir.varbanov@linaro.org>,
linux-media@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: Philipp Zabel <p.zabel@pengutronix.de>,
Ezequiel Garcia <ezequiel@collabora.com>,
Paul Kocialkowski <paul.kocialkowski@bootlin.com>,
Nicolas Dufresne <nicolas@ndufresne.ca>,
Tomasz Figa <tfiga@chromium.org>
Subject: Re: [PATCH] v4l2-ctrl: add control for thumnails
Date: Thu, 4 Jun 2020 11:08:48 +0200 [thread overview]
Message-ID: <544b19dd-4883-bae0-b488-46c856eb207d@xs4all.nl> (raw)
In-Reply-To: <d02c6cd0-a502-dc52-519e-54b6328d5373@linaro.org>
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.
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.
>
next prev parent reply other threads:[~2020-06-04 9:09 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-26 8:54 [PATCH] v4l2-ctrl: add control for thumnails Stanimir Varbanov
2020-05-26 12:04 ` Hans Verkuil
2020-05-26 21:53 ` Stanimir Varbanov
2020-06-04 9:02 ` Stanimir Varbanov
2020-06-04 9:08 ` Hans Verkuil [this message]
2020-06-04 12:34 ` Stanimir Varbanov
2020-06-04 12:56 ` Hans Verkuil
2020-06-04 12:57 ` Tomasz Figa
2020-10-13 12:52 ` Stanimir Varbanov
2020-10-13 13:12 ` Tomasz Figa
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