[lug] video formats question

[Calvin Dodge]

On Fri, Feb 04, 2005 at 02:43:29PM -0500, Daniel Webb wrote:
> I have several old Thinkpad 600Es that I use as VNC terminals to my faster
> workstations at home and school.  This does everything I want most of the
> time, but I would like to be able to watch video over them if possible.  I
> know that any of the high-compression formats are out of the question (this is
> a Pentium II 200 Mhz), but I wonder if this is possible if I transcode to
> mpeg1 or mpeg2 and watch that?  I'm only interested in normal TV resolutions
> and framerate, nothing fancy.

Well, here's one data point for you.

I just set up a PII 466 as a MythTV client.  With the embedded ATI adapter and Xorg, 
displaying stored MP4 files (TV resolution, which I _think_ is 320 by 240) 
at 640 by 480, it used about 80-90% of the CPU.  With the Nvidia module 
(necessary to do TV-Out on my Nvidia card) it runs at 95-100%.

The raw data rate is about 250-270 KB/second.

I assume if you ran it at the actual size (320 by 240), it might consume somewhat less
CPU time.

The above info is true IF your video chipset supports "xvinfo". My laptop doesn't (it
doesn't like the xorg "nv" driver, and I haven't tried the Nvidia module on it yet, so
it's running the generic "vesa" driver), and it drops frames when running the 
MythTV client (and that's with a 1.6 GHz celeron).

I don't know if a different compression scheme would really help you - at the 
decompression end I _think_ most of the time is spent creating and painting pixels, 
rather than decompressing the images. I saw little difference in CPU time at the
client end between MP4 and RTJpeg (real-time jpeg, which takes about 4 times as much
space).

OTOH, my laptop DOES display DVD movies in Linux without frame drops, and (IIRC) DVDs
are encoded in MPEG2 (somebody please correct me if I'm wrong). So MPEG2 _might_ be
doable on your laptops (at low resolution, anyway).

I guess if I were in your shoes, I'd try the suggested video operations on the fastest
computer available to me, and try to extrapolate the CPU usage on the laptop (on the
admittedly shaky theory that CPU power scales with MHz, 30% of a 1 GHz CPU would translate
to 100% of a 300 MHz cpu).  

This is all assuming the video player program is running on the laptop itself.  I _can_
run videos to my diskless workstations at 320 by 240, but I think 640 by 480 would use more
than twice my available network bandwidth.

And I've rambled on enough for now.

Calvin
-- 
Calvin Dodge
Certified Linux Bigot (tm)
http://www.caldodge.fpcc.net