[pvrusb2] recommendation for just watching tv

[tombreit]

hi,

thanks a lot for this detailed description! i will try to fiddle out if 
a no-pvr-solution might better fit my needs...

but when i'm back in the pvr-camp, i'll happily try your driver.

greetings from germany,
thomas



Am Mittwoch, den 16.11.2005, 22:36 -0600 schrieb Mike Isely:
> On Thu, 17 Nov 2005, tombreit wrote:
> 
> > hi,
> >
> > i'd like to just watch tv on my laptop - but i'm a little bit confused
> > about the usb-solutions for "my" linux (debian testing/unstable).
> >
> > you guys might be more involved in this hauppauge pvr usb2-thing :-)
> > ... and could perhaps give me some recommendations about this (or
> > another?) analog-usb-tv-box?
> >
> > is this device also suitable for live-tv-watching in good quality? or is
> > it primarily for recording? it's not about getting it to work on linux,
> > just about quality and suitability.
> >
> > sorry, you see, i'm really confused :-)
> > looking forward for some suggestions,
> > thomas breitner
> >
> 
> Here's some info from where I'm sitting:
> 
> There are two basic types of video capture strategies:
> 
>    1. Digitize raw video frames and make that available to applications.
> 
>    2. Digitize raw video and THEN hardware-encode that into a nice standard 
> mpeg2 video stream.
> 
> There are two basic types of video capture devices:
> 
>    A. Devices which are PCI cards and must be inserted into the computer.
> 
>    B. Devices which are external by nature and communicate with the 
> computer through a USB connection.
> 
> There are tuners out there on the market in each combination of strategy / 
> type.  There are some plusses and minuses to each choice.  For example...
> 
> If you have a laptop, you're mostly limited to USB devices (choice B).
> 
> PCI cards however seem to have more mature drivers in Linux.  Video4Linux 
> just recently seems to have started directly supporting a range of USB 
> capture devices.
> 
> Raw uncompressed video capture (choice 1) requires a lot of bandwidth, a 
> lot of storage space, and the formats are not all that well standardized. 
> Also, if one is going to try to "store" such video data, the file may 
> require additional metadata encoded in order to properly delimit frames. 
> Cards which only provide the uncompressed video therefore tend not to be 
> great choices for use in a PVR - typically with such a card you still want 
> to store mpeg2 anyway (rather than trying to mess with raw frames) so 
> you're left having to do the encoding in software.  Software mpeg2 
> encoding is expensive; you need a big machine to do that in real time.
> 
> Using a device which directly generates mpeg2 video (choice 2) is far more 
> friendly for bandwidth purposes and is mpeg2 data is easily stored in a 
> file since it's just a byte stream with all required metadata already 
> embedded within it.  This makes devices which emit mpeg2 data ideal 
> devices for PVR applications - you can build a nice PVR without having to 
> configure a hugely powerful PC which is nice because then you use smaller 
> fans (or no fan) which is a lot more amenable to a home theater 
> environment.
> 
> On the other hand, mpeg2 is not a good choice if you just want to "watch" 
> TV and not record it.  Why?  Because if you are starting with an mpeg2 
> stream then you have to decode that back to video frames before displaying 
> it and that typically requires a software decoder setup (which still 
> requires far less CPU than a software mpeg2 encoder).  A device which 
> spits out raw uncompressed frames is a much better choice here because 
> there the data is already in a form that you can display fairly easily. 
> For just "watching TV" there's no need at all for mpeg2.
> 
> You can get better performance characteristics out of a PCI device than a 
> USB device (i.e. more bandwidth, less latency).  This means that raw 
> uncompressed video capture cards are more common for PCI (and a lot 
> cheaper) than corresponding USB devices.  If you are trying to capture 
> broadcast quality video, USB 1.1 just doesn't have enough headroom.  USB 
> 2.0 has plenty, but these devices are not as common.  For an mpeg2 stream, 
> USB is fine - in fact even USB 1.1 is good enough in most such cases.
> 
> One last and very important consideration as well is that many TV 
> applications in Linux simply can't handle mpeg2 streams.  Such apps are 
> really designed to expect and use raw video frames, and are tuned to 
> genlock against the incoming frames and essentially just map the data into 
> an X window.  The excellent tvtime application is an example of this, 
> though I've heard rumors that the tvtime developers may be adding an mpeg2 
> decoder for it (and that is NOT a trivial feature to add).  The xawtv 
> application used to just do raw video frames, but the 4.x development 
> branch (which is unfortunately not very stable) adds mpeg2 video decoding. 
> mplayer of course can handle just about anything :-)
> 
> So, with all that said, if you are on a laptop, then that pretty much 
> rules out PCI devices and you are left with USB.  The Hauppauge "WinTV PVR 
> USB2" device (which is what the pvrusb2 driver of course is for) will work 
> for you, but it is mpeg2 at its heart and thus you won't be able to use it 
> with tvtime.  An alternative device you can try is the Hauppauge "WinTV 
> USB2" (no "PVR" in the same).  This is a *completely* different device 
> than the PVR USB2 that I know so well, however the V4L maintainer is 
> rapidly building up a solid driver for it.  Something like that might work 
> well for you, since you don't plan on recording anything.
> 
> Another thing you might want to consider is that maybe you don't want to 
> forclose the opportunity to record in the future.  Also realize that if 
> you ever want to run an application which can "pause live TV", then you're 
> back in the PVR camp and you'll really want something which can encode 
> mpeg2 video in hardware.  That of course brings you right back here. 
> MythTV might be a gorilla of an application which is a pain in the butt to 
> set up, but it is *sweet* once you have it running.  Using MythTV has 
> completely changed the way I watch TV.
> 
> Hope that helps...
> 
>    -Mike
>