Re: [ANNOUNCE] experimental alsa stream support at xawtv3

From: Hans Verkuil <hverkuil@xs4all.nl>
To: Mauro Carvalho Chehab <mchehab@redhat.com>
Cc: Linux Media Mailing List <linux-media@vger.kernel.org>,
	Devin Heitmueller <dheitmueller@kernellabs.com>
Subject: Re: [ANNOUNCE] experimental alsa stream support at xawtv3
Date: Tue, 24 May 2011 08:50:34 +0200	[thread overview]
Message-ID: <201105240850.35032.hverkuil@xs4all.nl> (raw)
In-Reply-To: <4DDAC0C2.7090508@redhat.com>

On Monday, May 23, 2011 22:17:06 Mauro Carvalho Chehab wrote:
> Due to the alsa detection code that I've added at libv4l2util (at v4l2-utils)
> during the weekend, I decided to add alsa support also on xawtv3, basically
> to provide a real usecase example. Of course, for it to work, it needs the
> very latest v4l2-utils version from the git tree.

Please, please add at the very least some very big disclaimer in libv4l2util
that the API/ABI is likely to change. As mentioned earlier, this library is
undocumented, has not gone through any peer-review, and I am very unhappy with
it and with the decision (without discussion it seems) to install it.

Once you install it on systems it becomes much harder to change.

Regards,

	Hans

> I've basically added there the code that Devin wrote for tvtime, with a few
> small fixes and with the audio device auto-detection.
> 
> With this patch, xawtv will now get the alsa device associated with a video
> device node (if any), and start streaming from it, on a separate thread.
> 
> As the code is the same as the one at tvtime, it should work at the
> same devices that are supported there. I tested it only on two em28xx devices:
> 	- HVR-950;
> 	- WinTV USB-2.
> 
> It worked with HVR-950, but it didn't work with WinTV USB-2. It seems that
> snd-usb-audio do something different to set the framerate, that the alsa-stream
> code doesn't recognize. While I didn't test, I think it probably won't work
> with saa7134, as the code seems to hardcode the frame rate to 48 kHz, but
> saa7134 supports only 32 kHz.
> 
> It would be good to add an option to disable this behavior and to allow manually
> select the alsa out device, so please send us patches ;)
> 
> Anyway, patches fixing it and more tests are welcome.
> 
> The git repositories for xawtv3 and v4l-utils is at:
> 
> http://git.linuxtv.org/xawtv3.git
> http://git.linuxtv.org/v4l-utils.git
> 
> Thanks,
> Mauro.
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