[mythtv-users] MythTV channel buffer

Ivan Kowalenko ivan.kowalenko at gmail.com
Sat Apr 15 15:10:49 UTC 2006


On Apr 15, 2006, at 06.45, Felix Rubinstein wrote:

> I reply to this post as Stef understood me better than anybody.
> I use hauppauge pvr 150 running on fedora core 5 and I use the  
> latest and greates 0.19 downloaded from svn and compiled.
>
> I live outside US and don't have EPG functionality in MythTV yet as  
> didn't have time to get my hands dirty to parse XML from local  
> content provider. I have TV and satellite receiver and 2 remote  
> controls for receiver and MythTV. Receiver is connected to my PVR  
> via S-Video and PVR to TV using S-Video.
> Since MythTV is not fed with EPG, I use my receiver to help me see  
> shows scheduling, using receiver's remote control and on any key  
> press I get a popup showing me the starting and ending time of the  
> show and short description.
> Now, suppose I like tennis and I watch eurosport, and suppose  
> MythTV is on, and suppose it's 10 a.m. I want to know when there  
> will be tennis if at all. I press a button on receiver remote  
> control to see what show is at 10 a.m. I get delay of 4 secs until  
> I see that from 10 to 11 a.m. there is a soccer, then I press next  
> and only after 4 secs of delay I see that there is some other show,  
> etc. Now interleave 4 sec delay for every key press on my satellite  
> remote control all of you would understand that it's unacceptable!

Dude, I use a separated front-end/back-end configuration on a hack- 
meat network and a front-end with less than optimal RAM. It takes me  
about ten seconds to get a LiveTV stream. If I wanted to browse the  
channels, I'd pull up the EPG. It sounds like you could save yourself  
a lot of grief if you just got up and figured out how to get the XML  
parsed for your country. Trust me, once you do that, your MythTV  
experience will be MUCH better. At this point, I don't watch LiveTV  
at all: I just see what's going to be during the next two weeks, and  
tell MythTV to record it for me. That's kind of the idea of a PVR: to  
free yourself from the scheduling restraints of traditional TV.

>
> If you say that I should first to see the scheduling and only then  
> to turn on the MythTV, I'd answer I don't want to play with S-Video  
> connectors, acceptable wish, right?
> I treat MythTV as a generic program, otherwise I would add lots of  
> cron jobs for:
> cat /dev/video0 > somefileX
> for every show I want to watch later on, BTW, it's an answer to  
> those how say I use it this way or other way, is it a generic or not?
>
> All of you, would it be acceptable if you move a mouse and get 4  
> secs delay of mouse coursor, or if you press a button on a keyboard  
> and get it shown after the same delay?

Actually, I've been in situations like that. I've used VNC to view  
networked computers, even over the internet. I've gotten a few  
seconds of lag (frame compression overhead, internet overhead, frame  
decompression overhead) and still found the computer perfectly  
acceptable for things like word processing. If it were a local  
machine, and not passing through something else, then, no that would  
be unacceptable. But, since I'm doing this in a way that's KNOWN to  
create overhead and lag, I modify my expectations.

> It's funny when I hear that there are people who have smaller  
> delay, any delay is unacceptable!
> When I say unacceptable I don't demand anything, and I'm thankful  
> to all of you for attention and to any developer who created  
> MythTV, I'm here to help, but unfortunately my hands are too much  
> dirty on hacking other things.
>
> BTW, my 3 years old Philips has all this, as you call, fancy  
> functionality: pausing rewinding, etc. with 0 (zero) delay!

Yes, and they're all custom made parts, not something put together  
with off-the-shelf components. The only delay is in creating the  
stream. Even on my XBox Front-end (64 MB of RAM, only!) I can pause,  
rewind, and fast forward with no delay. The only delay is in  
buffering the stream, which is a requirement given the architecture  
of MythTV (that front-end and back-end need not be on the same machine).

> All I wanted is to setup the PVR to my friend who doesn't have lots  
> of experience in Linux.
> What I mean is that instead of having many features like games and  
> weather report, I'd like as a professional, for MythTV to do one  
> thing but to do it well, instead of many half-well!

I'm afraid I have to differ. I live in a family where if I wasn't  
around, the computer would have broken years ago, and been abandon.  
They have no clue how to work Linux, and wouldn't know a CLI if it  
smacked them in the face. They use MythTV sometimes, and when they  
do, they have no problem. In my opinion, MythTV does things quite  
well. MythWeb is so fully developed that it could practically replace  
the front-end for many features, the recording system is efficient  
and simple,

>
> If you open documentation of MythTV http://www.mythtv.org/docs/ 
> mythtv-HOWTO-1.html
> you'd see the first bullet says the following -
>
> MythTV has a number of capabilities:
> * You may pause, fast-forward and rewind live Television.
>
> Did you point out live TV, not buffered for 4 secs, once again live  
> TV!!!
> Live TV is a zero-delay stream of bits.

Yes, a zero-delay stream of bits. Of course, if you weren't relying  
on your stream to be changing when you interacted, those four seconds  
wouldn't matter. Moreso, you forget to take into account the usual  
overhead: start the buffer, load playback software, load the OSD,  
acquire the screen, put the front-end away, find the current program  
in the database, parse the database information so it can be human  
readable, begin playback, display the OSD. When you're building  
something out of consumer hardware, you have to expect some kind of  
sacrifice compared to something that's been built out of custom  
hardware and specialized software in some R&D lab with millions of  
dollars to experiment with.

>
>
>
> On 4/14/06, Brad Benson <bbenso1 at gmail.com> wrote:
> On 4/14/06, Stef Coene <stef.coene at docum.org > wrote:
> stand.  What benefit are you getting from watching TV under
>
> > Myth?  You're not using Myth to change channels and you're not  
> talking
> > about recording stuff, just watching TV.  So why bother doing  
> through Myth?
> >  Just use your TV.

I'm starting to wonder this myself. Stef seems to sum it up properly.

> Mythtv knows the name of the show, short description, when it will  
> ends, ...
> That's why I should use live tv.  So you know what you are watching.
>
> Yes, Myth does know that if it's set up correctly.  However, the OP  
> said he isn't using Myth to change channels, he's doing it directly  
> via his STB.  So, when he changes channels on the STB he has a  
> several second delay while the previously buffered content clears  
> out and he *still* doesn't know what he's watching.  Unless, of  
> course, his STB has it's own EPG in which case my original question  
> remains:  Why not just use your TV?

And so does Brad. Why do you need Myth? It seems like you installed  
one app with a great sum of options built to do several things, and  
then complain that you don't want those options. If all you want is  
the pause/rewind function, you might as well just go

# cat /dev/video0 >file.mpg
# mplayer file.mpg

Because that should reduce a lot of overhead. Of course, there's  
still the possibility you'll have to wait as much as four seconds for  
MPlayer to load up.
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