latency

[vitaminman]

Hello,

Brand new to GBPVR, this is my first attempt at making a PVR.

Setup:
Hauppauge 250 tv card
Intel se-440bx motherboard
PIII 866mhz
384mb RAM
60gb HD, split into 2 partitions (1 for windows/programs, 1 for files)
GBPVR 09208
windows xp pro sp2
matrox g400 dual head
MediaMVP

So far everything is working well, after a bit of trial and error I was able to get the video signal from my Scientific Alanta digital cable box into the computer and back out to my MVP.

Here is the problem: there is a considerable amount of 'latency' between me hitting a button on the cable box remote and the results displaying on the televsion via the MVP (about 3 seconds).

I'm not too concerned with the ability to pause/rewind/ffwd my television; in fact, I'm quite happy to get rid of that feature if it would allow me to 'surf' with the least amount of delay possible.

As I'm new to this, I'm not sure where to start in the Configuration program.In the audio world, we have the same sorts of problems with soundcards not being able to monitor signals from their inputs in real-time because of all the work involved with passing the signal from the input to the driver to the os then back to the driver then back to the output.

In order to compensate, some soundcard manufacturers offer 'low-latency' drivers which bypass the operating system and allow the signal to only have contact with the host software. There are settings for the driver which allow the user to customise the degree of latency control in terms of milliseconds or buffers, or it will allow the signal to completely bypass the host software. The tradeoff is between speed and quality; the lower the latency, the higher the chance the audio will drop out or stutter.

1. Is there a way to completely 'turn off' the ability to pause/rewind/ffwd television so that there is no need for the video signal to go anywhere but back to the MVP?

2. Barring that, is there a way to turn down the delay/buffers to minimize the amount of stuff that gets passed around before being sent to the MVP?

3. Do encoding/decoding quality settings effect the speed at which a signal is passed to the MVP, and if so, does it effect the speed at which the computer passes the signal to the network port, the speed at which the signal travels along the network cable, or the speed at which the MVP displays the signal?

Thanks in advance,

Nick

[sub]

1. Is there a way to completely 'turn off' the ability to pause/rewind/ffwd television so that there is no need for the video signal to go anywhere but back to the MVP?

Not with the MVP. The MVP is only really designed to playback files, so GB-PVR's live tv support for the MVP is effectively playing back a file as it records.

When you're viewing on your PC monitor in live preview mode, there is effectively no delay (very short delay if you're using encoder pass-through).

2. Barring that, is there a way to turn down the delay/buffers to minimize the amount of stuff that gets passed around before being sent to the MVP?

As I said above, its just playing back a file when you watch tv. The is a configurable 'MVP live tv pre-play delay', which is the amount of time GB-PVR will wait after the recording starts, before telling it to start playback. The default is 500ms (in addition it takes about half a second or so to start the recording). You can reduce this delay slightly, but its not really advised as it some times caused the MVP to think it has reached the end of file and it returns to the main menu.

Also, the Hauppauge software that runs in the MVP expects that the file already exists, so it tries to read ahead (buffer) before it starts playback. Of course this part of the file doesnt exist yet, so GB-PVR has to wait for this part of the file to be written to disk before supplying it to the MVP. This typically takes a bit more than a second, and isnt something I have control over.

3. Do encoding/decoding quality settings effect the speed at which a signal is passed to the MVP, and if so, does it effect the speed at which the computer passes the signal to the network port, the speed at which the signal travels along the network cable, or the speed at which the MVP displays the signal?

Probably. Try a few bitrates and report back on which works best for you.

[vitaminman]

Sub,

Thank you for your reply.

1. I see! The MVP only plays back files...so in essence, GBPVR is taking a stream from the 250 and passing it along to the MVP as a file; data must exist before it can be passed, and hence some delay. And the MVP needs time to receive/buffer this before passing it onto the RCA outputs, which equals MORE delay. Totally understandable and completely out of anyone's control (except Hauppauge).

2. Are there alternatives for getting a signal from my computer to a television besides the MVP? While I do think it's cool to be able to watch recorded programs using it (I have used the WinTV2000 app before with great success), there is more than one way to skin a cat, and I don't have to use it...

Take care,

Nick