View Full Version : Channel change latency

2008-08-14, 08:47 AM

Got my PCH delivered yesterday, followed the instructions and got everything set up in what I believe is "the correct way". Initially I didn't get live TV and soon realised you have to enable the "Minimal OSD" mode to stop socket errors in the server process.

The GB-PVR interface on the PCH is a much nicer place to be than the PCH native interface but is there any way of speeding up channel changes and reverting back to the guide? I notice on the OSD demo thread, when I watch the YouTube video the channel change appears to be instant. I use a component output and changing channels currently involves three or four screen flickers (presumably whilse reolutions and refresh rates are changed) and about 12-15 seconds of black screen.

Also, the same seems to happen when either there's a reception glitch or the break between one programme and the other on the same channel, which is very annoying.

Are there any option or tweaks to avoid this?



2008-08-14, 02:33 PM
The delay between channels and program changes is the reality of the current implementation. Basically the NMT design is to act like a web browser and launch and exit a media viewer. The delays you see wouldn't be out of place or even seem too odd on your PC if you were launching WMP for videos from your browser, one at a time. Obviously everyone wants more than this, and I have asked Syabas for the detailed infromation needed to make this happen, but I have been waiting for a very long time. However, as I have been saying for a while now, there have never been any guarantees that anything would work on the PCH, and I am actually pleased with how much can be done, everything considered.

Regarding channel/program changes, a couple of months ago I proposed a solution to sub that would typically cut these delays down to under two seconds using the Syabas implementation. Sub has his own ideas on how to try and improve this too, but as you are probably aware, sub is busy with other work and major improvements will have to wait until he has time. Let's wait and see what sub and I can do some more focused work.

Because you mentioned the recent YouTube demo this wasn't meant to show something that I would want to implement in production on the NMT, although YouTube doesn't do it justice, it acctually looks quite good. What the demo highlights ist that the latency problem you are seeing isn't in mvpmcx2, or in GBPVR writing files as a couple of people has suggested, it is the mono process. It also shows that if we were in the "old" SD MPEG-2 world of the MVP I wouldn't have any difficuly with channel changing, it probably would turn out to be faster. HD and digital is a new world which is why the PCH is required in the first place.

Regarding tweaks, about all you can do is work on reducing those glitches that cause the video to stop.


2008-08-15, 07:50 AM
Hi Martin,

Thanks for your reply. The channel change is fine and something which I think you easily get used to, it's just after seeing the channel change in your demo I wondered if there was something I had configured wrong.

I don't think there's anything I can do directly about the breaks during programme changes as I think this is something GB-PVR does when a guide channel changes (changes the filename). Again though, this is not something which is unbearable as generally only idents are playing at that time.

I'm impressed at how stable it is when it's all up and running, thanks for a great product.