linux-kernel - Re: [PATCH] v4l: add V4L2_CID_MPEG_VIDEO_FORCE_FRAME

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Date:	Thu, 14 Jan 2016 10:02:23 -0500
From:	Nicolas Dufresne <nicolas.dufresne@...labora.com>
To:	Kamil Debski <k.debski@...sung.com>,
	'Wu-Cheng Li' <wuchengli@...omium.org>, pawel@...iak.com,
	mchehab@....samsung.com, hverkuil@...all.nl, crope@....fi,
	standby24x7@...il.com, ricardo.ribalda@...il.com, ao2@....it,
	bparrot@...com
Cc:	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-api@...r.kernel.org
Subject: Re: [PATCH] v4l: add V4L2_CID_MPEG_VIDEO_FORCE_FRAME_TYPE.

Hi Kamil,

Le mercredi 13 janvier 2016 à 17:43 +0100, Kamil Debski a écrit :
> Good to hear that there are new codecs to use the V4L2 codec API :)
> 
> My two cents are following - when you add a control that does the same work
> as a driver specific control then it would be great if you modified the
> driver that
> uses the specific control to also support the newly added control.
> This way future applications  could use the control you added for both new
> and
> old drivers.

When i first notice this MFC specific control, I believed it was use to
produce I-Frame only streams (rather then a toggle, to produce one key-
frame on demand). So I wanted to verify the implementation to make sure
what Wu-Cheng is doing make sense. Though, I found that we set:

  ctx->force_frame_type = ctrl->val;

And never use that value anywhere else in the driver code. Hopefully
I'm just missing something, but if it's not implemented, maybe it's
better not to expose it. Otherwise, this may lead to hard to find
streaming issues. I do hope we can add this feature though, as it's
very useful feature for real time encoding.

cheers,
Nicolas
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