[mythtv-users] Plextor Mpeg4 Hardware Encoding & N00b Requesting Advice

Bryan Miller bmiller at westinghousedigital.com
Tue Dec 21 03:22:53 UTC 2004

Hello to all,

Does the hardware from plextor run under Myth?

It says it has hardware encoding for mpeg4, and it has a firewire port. 
If it has firewire, is it merely telling the device to record, and it 
spits it out as a stream through the FW port? Kinda like an on/off 
switch... Prolly more coding involved, but I would figure something 
like that would be a little easier to code than the 150. Am I wrong? I 
haven't looked. Again, I'm TEH N003. :P

I haven't subscribed long enough to return any results for a search 
through my local e-mail. The list archive doesn't have a search 
function, so sorry if this is a repeated question.

As for the advice...

I am planning to build a system, and I was originally looking at one 
350 and a 250 with a 6800 Ultra. Heard that the VPU was broken on the 
6800, but I doubted whether there would be a linux driver for it even 
if the VPU worked. I'm ultimately interested in being able to play 
1080i/p content on the machine, so the throughput of the videocard was 
a deciding factor. Will the 350/250 be able to decode this kind of HD 
content? Aside from 1080i content, I would -like- to use this machine 
to save shows to disk, but I continually see 1GB/hr. What is the 
quality of the recordings? I have seen files that are typically 350megs 
for one hour. I'm guessing they are transcoded down to a lower res. I 
would also be interested in archiving seasons onto DVD, but 4 shows per 
DVD versus 12 sucks. True, DVDs are relatively inexpensive nowadays.

However, if I were record 1080i content, would I be able to accomplish 
this using an FX55 with one of the tuner cards? Would I have to use a 
simple frame grabber card and then encode after the data has been saved 
onto the HDD? (I figure if there is no encoding before it hits the HDD, 
it would eat disk space like nothing else. If so, what kind of space 
consumption am I looking at?) What would the requirements be for 
recording 1080i content? Am I only limited to commercial hardware that 
cost a lot?
I wouldn't be saving a lot of 1080i content--I would only be interested 
in saving particular shows from ATSC or HD-DTV for later editing to 
create some montage of clips for a demo file.

Also, I was planning to have a SCSI drive with the system installed on 
that with a SCSI DVD ROM, so as to free up as much CPU cycles as 
possible. (I never really liked the fact that IDE/ATAPI/SATA takes up 
your main CPU just to read and write data.) ...Anyway, is there a way 
to configure Myth to temporarily store the data on the SCSI while 
recording and also when you want to play? I.E. it records your shows to 
the scsi drive, and during an idle period moves it over to the 
secondary storage device (external FireWire, in my case). For playing, 
you would select what show you were going to view and it would transfer 
over the file to the scsi drive? I was thinking about pre-viewing 
transfer for 1080p content.  Course, after it's moved it to the 
secondary drive, it keeps track of it for later viewing. Maybe this 
could be done with symlinks. I haven't bought the entire system yet, so 
I haven't been able to test Myth. I'm not sure of its capabilities. 
Just trying to figure things about beforehand.

Hrm. I was just thinking... What if Myth could store data (when a 
setting is checked) on a network drive in chunks of 1gig. Then, a 
script running on a Dual G5 2G would encode the files into a mpeg4 
video file and delete the read 1gig chunks as it goes? I dunno. Just 
thinking aloud.

Any help or advice would be greatly appreciated. Thanks in advance.


Bryan Miller							Westinghouse Digital Electronics
Field Applications Engineer				16257 E. Gale Ave.
Ph: 626.333.9252 x117					City of Industry, Ca 91745
Fax: 626.333.9272

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