V4L for DVB ASI

V4L for DVB ASI

[Dinesh Bhat]

Hello,

We are DVB ASI PCI/PCIe card manufacturers in Canada. Some of you may 
have heard about our distributors: DVEO/Computer Modules. We encourage 
open source and use open source to develop our Linux products. I have 
been doing some research on getting our already open sourced DVB ASI 
drivers to work with either v4l or the regular DVB API.

I had asked a question to the community a while ago and have had few 
responses. The question was mainly to find out if there is any interest 
in the community towards this goal. We will be happy to work with you. 
The initial response was to work on v4l as opposed to the DVB API. Since 
the cards support PID filtering and other transport stream analysis, I 
am encouraged to use DVB API instead of V4L because of TS feature 
support at the software level. But then I could be wrong since I have 
not done a lot of research on these two APIs. Sigmund Augdal had listed 
out the pros and cons to my previous question:

Use the DVB Api:
pros:
 * you can take advantage of the software pid and section filters in the
dvb framework
 * if your device supports hardware pid/section filters, apis will be
available to take advantage of them
 * userspace applications that handle mpeg2 ts often use this api, and
would be easy to adapt.
cons:
 * you might need to extend the apis to handle asi cards

Use the v4l2 api:
pros:
 * semantics are well defined.
 * provides an extensible api using so called "controls"
cons:
 * adapting user space applications will be more difficult
 * no reuse of software filters

If Anybody wants to look at the drivers, they are available at http://www.linsys.ca in customer support section.

Thanks for any advice and help.

Kind Regards,

Dinesh

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Fx: 204-697-2417
www.linsys.ca

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Re: V4L for DVB ASI

[Hans Verkuil]

Hi Dinesh,

On Thursday 24 July 2008 18:36:27 Dinesh Bhat wrote:
> Hello,
>
> We are DVB ASI PCI/PCIe card manufacturers in Canada. Some of you may
> have heard about our distributors: DVEO/Computer Modules. We
> encourage open source and use open source to develop our Linux
> products. I have been doing some research on getting our already open
> sourced DVB ASI drivers to work with either v4l or the regular DVB
> API.
>
> I had asked a question to the community a while ago and have had few
> responses. The question was mainly to find out if there is any
> interest in the community towards this goal. We will be happy to work
> with you. The initial response was to work on v4l as opposed to the
> DVB API. Since the cards support PID filtering and other transport
> stream analysis, I am encouraged to use DVB API instead of V4L
> because of TS feature support at the software level. But then I could
> be wrong since I have not done a lot of research on these two APIs.
> Sigmund Augdal had listed out the pros and cons to my previous
> question:
>
> Use the DVB Api:
> pros:
>  * you can take advantage of the software pid and section filters in
> the dvb framework
>  * if your device supports hardware pid/section filters, apis will be
> available to take advantage of them
>  * userspace applications that handle mpeg2 ts often use this api,
> and would be easy to adapt.
> cons:
>  * you might need to extend the apis to handle asi cards
>
> Use the v4l2 api:
> pros:
>  * semantics are well defined.
>  * provides an extensible api using so called "controls"
> cons:
>  * adapting user space applications will be more difficult
>  * no reuse of software filters
>
> If Anybody wants to look at the drivers, they are available at
> http://www.linsys.ca in customer support section.

Since I am heavily involved in the MPEG support for V4L2 I suspect that 
I am probably the right person to look into this. I must have missed 
this the first time you mailed it, probably because the subject didn't 
mention V4L. I am not involved in the DVB API, with the exception of 
the MPEG decoding part of it (dvb/video.h, dvb/audio.h) since my ivtv 
driver uses that for the MPEG decoding.

Looking over the functionality of ASI I see (correct me if I am wrong) 
that it is basically a transport standard for MPEG-TS streams as used 
in DVB applications. There is no routing, tuning or (de)modulating 
involved. The device is fed one or more MPEG-TS streams, they are muxed 
and timestamped and sent out over the ASI connection. And it can also 
receive an MPEG-TS stream and is able to demux that depending on the 
PIDs.

In my personal opinion I would say that this falls under the V4L API 
(with perhaps some use of the video.h/audio.h interfaces from DVB). 
Regardings the cons that are mentioned: since there is no standard for 
the ASI API all user space apps need to be converted anyway if a 
standard would appear. And as I understand it, any filtering is done in 
hardware.

Looking at the ioctls of your driver I would say that most if not all of 
these can be implemented as controls. Based on the admittedly limited 
information I have I see no obstacle of getting this into the v4l 
framework.

Regards,

	Hans

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