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View Full Version : Buffer Dumps: Is this really necessary?


TomCat
07-12-03, 01:13 PM
No, would be my educated guess.

I'm not sure where the conventional wisdom of dumping the buffer on a channel change (or power off) came from, but I can think of no technical reason why its needed. If you are happy with the hard drive spinning 24/7 (and many of us are) then what's the problem? I can see no reason why using well-designed OS software, a PVR can't just keep recording merrily along through channel changes and whatnot, just like it does during signal interruptions. My guess is that the concepts of HD recording on PVR are a little thick for consumers in the first place, and that buffer management had to be simple and automatic when PVR's first came out. But in reality, just about anything is possible. All it should take would be the addition of a few lines of code to handle the mildly-more-sophisticated file management chores.

In fact, I don't see any reason why the buffer can't be expanded to currently available space, sort of the way Replay does it (but Replay stops recording to save the BEGINNING of the buffer if you pause long enough). Not only that, but the programs that collect in the buffer could be listed in a page of the PVR listings. Saving just one program from that list after-the-fact would be problematic, since its part of a larger allocated media region, but that's not really a problem. DISH perfected rewinding into the past to save part of the buffer as a standard recording years ago, which is almost as good. Management of the programs recorded into the buffer could be pretty simple and automatic, using FIFO.

Here's what I envision. I leave my PVR on my favorite or some other strategic channel before I go to work, turning it off before leaving. Once back home, I turn it on to see that I have about, say, 6:30 of buffer space on that particular day, which has been filled with whatever was broadcast on that channel in the last 6 1/2 hours, presented to me in a PVR listings sub-page, possibly entitled "Currently Buffered Programs". Even if the cat walked on the remote in my absence, any inadvertant channel changes only change whats recorded and the buffer stays intact. I can either ignore the programs in the list, pick one or more to play back (being mindful of the time-sensitive nature of FIFO), or pick some portion of the buffer to turn into a permanent recording. What could be simpler, and why doesn't my current PVR offer this capability? Answer that, if you can.

Although I maintain quite a few professional hard-disk recorders daily as a part of my job, my technical familiarity with the processes surrounding MPEG encoding/decoding gives me no clue as to why this practice ever began (I blame Tivo!). Ironically, professional video servers never record to a PVR-like buffer (it makes no business sense) but there still seems to be no technical reason why a perpetual buffer could not be implemented even on them, but most particularly in new PVR design.

If anyone can shed light, has info or theories, I'd be interested to hear them.

gwynnebaer
07-12-03, 08:59 PM
One thing to consider is that with Dish PVR's, there is no MPEG encoding/decoding going on. The feed is already MPEG encoded when it arrives at the PVR, so there's not any additional work to be done other than to drop the data onto disk. In fact, if I understand the way the 721 works, it *only* plays data that's on the disk. That's the reason for the 3-5 second lag between channel changes:

1. change a channel
2. pvr stops dumping the current channel to disk, and starts dumping the new channel to disk
3. when enough data is on disk to begin showing it onscreen, the picture appears on the screen

Hence, since the pvr is already dumping to disk all the time, I think your idea is sound.

The problem I see is with maintaining space on disk for all the shows in your queue vs. filling the disk with buffered shows. It's not terribly complex to add up the recording time needed in the near future (just add up the time of the scheduled shows).

But what does the PVR do when it runs out of space, or when it is in danger of running out of space? What is the priority and how does the user get notified of what decisions the PVR had to make? A configuration screen where the user can pick what priorities should resolve this.

Or are we just dense and we don't understand the bigger picture here? :D

Jacob S
07-12-03, 11:15 PM
I would also like to see this and it has been on my website for a good while now. That is one thing that I liked about the Dishplayer, unlimited buffer. I would leave and come back and start from where I left off even though I did not have that much space on the hard drive I learned to keep the hard drive cleared out by watching my shows not too long after they come on. One could always upgrade the hard drive in the Dishplayer anyways.

They could have the folders idea implemented (also mentioned on my website in which people requested) and a folder could be for buffer then a drop down listing of the buffers by date, channel, or show, etc. You could set the priority manually of which ones get erased last (protect priority) or just be able to protect them just as you would recordings. I think a protect priority would be good for the regualr pvr events as well.