Re: [RFC, libv4l]: Make libv4l2 usable on devices with complex pipeline

[Pavel Machek <pavel@ucw.cz>]

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Hi!

> > Pavel,
> > 
> > I appreciate your efforts of adding support for mc-based devices to
> > libv4l.

Thanks.

> > I guess the main poin that Hans is pointing is that we should take
> > extra care in order to avoid adding new symbols to libv4l ABI/API
> > without being sure that they'll be needed in long term, as removing
> > or changing the API is painful for app developers, and keeping it
> > ABI compatible with apps compiled against previous versions of the
> > library is very painful for us.
> 
> Indeed. Sorry if I wasn't clear on that.

Aha, ok, no, I did not get that.

> > The hole idea is that generic applications shouldn't notice
> > if the device is using a mc-based device or not.
> 
> What is needed IMHO is an RFC that explains how you want to solve this
> problem, what the parser would look like, how this would configure a
> complex pipeline for use with libv4l-using applications, etc.
> 
> I.e., a full design.
> 
> And once everyone agrees that that design is solid, then it needs to be
> implemented.
> 
> I really want to work with you on this, but I am not looking for partial
> solutions.

Well, expecting design to be done for opensource development is a bit
unusual :-).

I really see two separate tasks

1) support for configuring pipeline. I believe this is best done out
of libv4l2. It outputs description file, format below. Currently I
have implemented this is in Python. File format is below.

2) support for running libv4l2 on mc-based devices. I'd like to do
that.

Description file would look like. (# comments would not be not part of file).

V4L2MEDIADESC
3 # number of files to open
/dev/video2
/dev/video6
/dev/video3
3 # number of controls to map. Controls not mentioned here go to
  # device 0 automatically. Sorted by control id.
  # Device 0 
00980913 1
009a0003 1
009a000a 2

We can parse that easily without requiring external libraries. Sorted
data allow us to do binary search.

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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