[linux-dvb] Re: streaming video over USB?

[Alex Woods <linux-dvb@giblets.org>]

On Tue, May 18, 2004 at 10:13:53AM +0200, Patrick Boettcher wrote:
> On Tue, 18 May 2004, Craig Procter wrote:
> > Is the video packetized by the USB device or is it sent in a constant
> > stream which the software on the PC then 'grabs' and decodes/shows on
> > screen?
> 
> For Twinhan VP7041 the dvb data is directly streamed to the software, and
> the software does the rest (So no special repackaging by the device).

For the Hauppauge DEC range, audio and video streams are streamed in a
proprietary format called PVA.  It contains MPEG ES packets.  Section data is
also packeted up.

> > Is there a 'universal' way which has been adopted for streaming
> > USB video or does each manufacturer have their own way of doing things?
> 
> Since the USB devices have different endpoint types (e.g. Hauppauge dec-t
> has isochronous EPs for data (Alex, correct me if I'm wrong), VP7041 has
> only bulk endpoints for everything) and so different access method, I'm
> not sure if a abstact usb driver is useful.

Indeed, the DECs use isochronous transfers data streams.  There definately
isn't a standard for streaming DVB data over USB.

> > (ie: software has to be tailored to each different USB video device).
> 
> No, in Linux the driver build an abstract framework for the applications,
> this could be possible in Windows as well, but I don't know.

It would be possible in Windows, but as far as I'm aware the software is very
much tailored to the device.

> Also is there a difference in the way the video is streamed if the source is
> analogue or digital TV?

I would imagine analogue TV is more likely to be streamed as plain MPEG,
whereas DVB hardware would prefer MPEG transport streams.  But it probably
varies widely depending on the hardware's capabilities.

Cheers,
Alex


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