[MEncoder-users] tv tuner card suggestions?

[Rich Felker]

On Wed, Sep 05, 2007 at 01:57:01PM +0100, Dieter wrote:
> > USB etc. probably requires a lot more cpu. I always get huge cpu load
> > from using usb storage devices, and tv capture has similar or higher
> > bandwidth requirements.
> 
> dd-ing from a USB disk to /dev/null for awhile gives
> 
> 2944139264 bytes transferred in 180.379007 secs (16321962 bytes/sec)
> 
> with the CPU 97.5% Idle.  A US ATSC broadcast is 19392576 bits/sec.
> So reading a maxed out channel over USB would use 0.37% CPU.
> This assumes that reading from a USB TV tuner has the same CPU overhead
> as reading from a USB disk, which might not be the case.  Add another
> fractional percent for writing that data to disk.  This with a CPU that
> was the bottom of the line 2 years ago and is probably no longer made.

Maybe it's a matter of the USB version in use. Here's my hardware (2
machines, both with very high load from USB):

USB Controller: Intel Corporation 82371AB/EB/MB PIIX4 USB (rev 01)
USB Controller: VIA Technologies, Inc. USB (rev 2)

> > US essentially does not have digital TV.
> 
> In the US, the FCC has required all TV stations to broadcast digital for
> quite awhile now.  I don't know if Jody is in the US or in some other country.

I think what happens is they "broadcast" the digital with a signal so
weak no one cat receive it except inside the city limits...

> > > > i want it to include an encoder on the card, so my cpu can be left in
> > > > peace
> > > 
> > > Note that watching a recording requires decoding, which also requires a lot
> > > of CPU, or decoding hardware.
> > 
> > This is misleading. Watching requires trivially small CPU load
> > compared to encoding (like 100mhz vs 1.5ghz). In fact my experience is
> > that just moving uncompressed video across the PCI bus is slower than
> > decoding the same video and moving it across the video bus (AGP/etc.)!
> 
> Xbitlabs tested this.   AMD Athlon 64 FX-60 CPU (2x2.60GHz, 2x1MB L2) +
> GeForce 7300 GS decoding 1080i takes 26.6% CPU.  A single CPU would thus
> take about 53.2%, and more if you have a slower clock rate, which is likely,
> since the FX chips are expensive high end chips.  And that is with whatever
> hardware assist they are getting from the GPU.  Given the lack of
> documentation on GPUs, the amount of hardware assist *BSD or Linux gets is
> zero, so CPU requirements probably go up even more.  100 MHz?  No way.

I'm talking about 480-line NTSC signal, not HDTV. The question was
about getting a card that encodes the analog signal and sends it
compressed ("i want it to include an encoder on the card" makes this
clear), versus a card that sends uncompressed frames over the bus.
HDTV was not involved in the topic at all.

Rich