some thoughts on /dev/video ...

[Ralph Metzler <rjkm@netcologne.de>]

Guido Fiala writes:
 > Of course making a standard device for video sounds good.
 > 
 > But what about different functionality?
 > 
 > Analog TV can not be recorded or played-back the same as dvb.
 > (not practicable, but theoretically)
 > 
 > So long it's not 100% compatible, it makes module-autoloading difficult, try
 > the following:
 > 
 > You have a bttv card and a dvb card - if you press the xawtv-icon
 > all the drivers should load automatically and it should open the right
 > /dev/video* device. Then you press the gVideo-icon and the same with the
 > dvb-modules. It should work independend from order.
 > 
 > How can we solve this trouble? The most easy would be a different device-major.

What exactly is incombatible between the io calls of the bttv and DVB drivers?
Grabbing via ioctl with the DVB driver will deliver a single
uncompressed picture exactly like the bttv driver.


Only read/write and tuning is different:

- tuning 
  gVideo (or xawtv) could be modified to look for the card capabilities and change
  the tuning behavior accordingly. (Itīs all open source, knock yourselves out :-)

- write
  bttv does not have it -> no icompatibility

  The IOMEGA BUZ driver has it, but for motion JPEG, so one should just ignore
  the data if the card cannot handle it
  
  The Stradis driver has it and at least the playback control io calls are
  compatible with the DVB driver. Now that the DVB driver understands
  PES directly this could be made fully compatible.

- read 
  bttv delivers VBI data in /dev/video, that should be changed anyway only to come
  out of /dev/vbi

   
So, what besides tuning is really that incompatible???

I donīt say one could not introduce a new device only for the DVB
features, but the V4L parts responsible for display on the screen and
grabbing single pictures are compatible and should stay available
via the V4L interface.


 > Another thing is the current modul-name identity for tuner.o and msp3400.o.
 > I know, it's work in progress, but is it intended that you need just one tuner.o
 > (and one msp3400.o) for all the different cards, with different tuners in your
 > system? Is it not recommended to change module-names?

The tuner driver of the DVB driver should be compatible with the
kernel driver and should work with the tuners bttv uses.
If not, please tell me. I donīt (and never did) use the tuner input of
the bttv driver much (only for testing) and donīt even have a Bt card
with tuner installed right now (I really have to get one of those new boards
with 6 PCI slots ...).

You can forget about the MSP34XX driver. The version which comes with
the DVB driver is an old version which once came with bttv. I did not
get around adding the features for the analog add-on module of the DVB-C card
yet.


Ralph