Rewind in RAM

[NumberFive]

Hi,

Don't know if this is possible with the current structure of the GBPVR programme, and I'm sure sub has thought of this, but what about the possibility of rewinding LiveTV using data from RAM.

I have Live Preview enabled in config because I find channel change too slow when disabled, but the rewind feature when disabled is really cool. If, when using Live Preview mode, the last 30 seconds (say) were kept in RAM and could be rewound, that'd be really cool. A 4 Mbps TV stream would only need about 15 Mb of RAM.

[whurlston]

It's might be "possible" with DirectShow but I doubt that it would be "feasible". It would be a really neat feature but I'm not sure that it would be worth the effort required to program it.

[reven]

you could try installing a ram drive (software that makes a virtual hdd from your ram), and then set that to your live tv buffer directory.

not sure how much faster it would actually be, but worth giving it a go

[johnsonx42]

agree this would be neat, but there are definitely technical reasons it wouldn't work. Live Preview mode simply connects the output of the tuner to the decoder/rendering chain, completely bypassing GB-PVR. So there's no way for GB-PVR to buffer any data, since it doesn't have it in the first place.

Using a ram drive for the live tv buffer in timeshift mode is an interesting idea, but I don't know that it would make anything much faster since the hard disk access itself probably isn't the determining factor. I'm guessing you might get away with less Live TV Pre-delay.

The other issue I think is that as currently implemented, timeshift mode requires the tv buffer drive to have enough free space to hold the entire program being watched, which for any form of HD would be huge, far beyond the capability of consumer-level mainboards and operating systems.

I wonder if it would be possible to devise a recording/playback method using a looping file where the file is a set size and data is simply written to the file continuously, discarding the oldest data in the file. If you could allocate a 2GB ram drive (probably the biggest practical size on a 32-bit OS), that'd be enough for about 15 minutes of buffer in US 1080i HD, more in lower resolutions or other TV systems that use H.264. If you get to the point where the current recording position approaches the play-back position (ie, you approach the point of overlap) then you just disable pause and rewind functions until the distance between the two increases above a certain minimum (ie, the user skips forward again).

Sub's far more likely to know than me whether it's possible to do that.

[NumberFive]

As I say, it's just an idea, but would be interesting to see if it was possible. The main reason I use the Live Preview is that channel change is too slow when it is disabled. I'm sure it's not the HDD slowing things down, probably just the need to set up a new Graph every time the channel is changed.

[whurlston]

The reason it is slow is because some of the video has to be buffered to the disk before playback can begin. With Live Preview, you don't need to wait for anything to be buffered.

[mvallevand]

Having really only used the MVP and PCH for live TV I find the 2 second delay more than worth any speed value gained in preview mode. I almost always want to rewind.

Martin