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

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Date:	Thu, 14 Jan 2016 14:02:13 -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, 'Andrzej Hajda' <a.hajda@...sung.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.

Le jeudi 14 janvier 2016 à 18:21 +0100, Kamil Debski a écrit :
> I had a look into the documentation of MFC. It is possible to force
> two types of a frame to be coded.
> The one is a keyframe, the other is a not coded frame. As I
> understand this is a type of frame that means that image did not
> change from previous frame. I am sure I seen it in an MPEG4 stream in
> a movie trailer. The initial board with the age rating is displayed
> for a couple of seconds and remains static. Thus there is one I-frame 
> and a number of non-coded frames.
> 
> That is the reason why the control was implemented in MFC as a menu
> and not a button. Thus the question remains - is it better to leave
> it as a menu, or should there be two (maybe more in the future)
> buttons?

Then I believe we need both. Because with the menu, setting I-Frame, I
would expect to only receive keyframes from now-on. While the useful
feature we are looking for here, is to get the next buffer (or nearby)
to be a keyframe. It's the difference between creating an I-Frame only
stream and requesting a key-frame manually for recovery (RTP use case).
In this end, we should probably take that time to review the features
we have as we need:

- A way to trigger a key frame to be produce
- A way to produce a I-Frame only stream
- A way to set the key-frame distance (in frames) even though this
could possibly be emulated using the trigger.

cheers,
Nicolas
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