What's the Big Deal About DVD Recorders?

I've seen numerous references to the soon to be released wave of DVD recorders (stand alone, not computer components). What I've not seen are specifications for any of these units, or the cost.

I'm no expert, but I do know that it is not trivial to make a DVD recorder. Specifically, how well could such a unit compress data on the fly? If the Replay TV / TIVO units are any comparison, there will be significant loss in picture quality. Also, will the data transfer rate of the drive mechanism support the rate of the data stream, or will the unit need a significant cache of memory, or a hard drive?

If you don't compress the data at all, what would be the capacity of the disc, and again, could the data rate be supported?

Anyway, I was just curious as to what these machines will be capable of.....

-Curt

[Chromy]

Yeah, they would either have to have a pretty powerfull processor and a large cache to accomadate for a variable bit stream to get a good recording time/performance rating. However, I imagine that you are probably right. To make the recorders affordable (relativly ) they would probably just offer a few different constant bit rate recording modes.

Chromy

[TampaFlyer]

> Replay TV / TIVO units

So the picture quality of these isn't that great? How does it compare to that of VHS? (I'm asking because none of the articles I've read about these gadgets said a word about the quality- the focus was on the features.)

I can't speak from my own experience on the Replay TV / Tivo picture quality, but I have read several accounts from other enthusiasts on various forums like this that do have the units.

The consensus opinion is that every mode results in at least some loss of quality, with higher compression modes (ie, longer total record time) having some significant picture quality loss.

I brought that up to address the issue that many probably expect DVD recorders to be magical devices that will allow us to record at qualities approaching that of pre-recorded DVDs. This will most certainly not be the case, due to the overhead involved with compressing and recording live video and audio onto the disc.

HDs will support a much higher data rate for recording than the DVD recorder would, I imagine, and I would expect that a DVD recorder would require some significant caching or temporary storage to buffer the stream to facilitate the MPEG encoding process.

This whole discussion just goes to show how little information the industry has provided concerning the specifications and features these so-called "DVD recorders" will have.

If Philips or someone has released such information, please point me to it.

-Curt

>I brought that up to address the issue that
>many probably expect DVD recorders to be
>magical devices that will allow us to record
> at qualities approaching that pre-recorded
> DVDs.

It'll be hard to respond until such units ship, but there is no reason that a home unit can't come damn close if not similar to a high quality DVD release.

Obviously there is no way that a home recorder will do VBR (variable bit) without a massively large HD and a ton of CPU/Processing power.

But allowing the user to record at set bit rates, say low being 2.5Mbits, medium 5Mbits, and high at 9.5Mbits will be the way to go. Obviously, the higher the quality, the less storage space will be available.

There are quite a few MPEG-2 hardware encoders on the market now that encode on the fly, and allow the user to set a constant bit-rate (but not variable like we'd all want). I've seen a 9Mbit encoded signal, and it looks virtually the same as a high quality DVD.

Of course there's no exact way to compare without taking the same source and doing a VBR on a high end machine.

As soon as you factor in VBR, the cost of these devices now starts at the $25k mark.

I feel that getting a great looking "DVD" is totally feasible, but there will be trade offs (limited disc space because of lack of VBR).

-Brian

But allowing the user to record at set bit rates, say low being 2.5Mbits, medium 5Mbits, and high at 9.5Mbits will be the way to go. Obviously, the higher the quality, the less storage space will be available.

There are quite a few MPEG-2 hardware encoders on the market now that encode on the fly, and allow the user to set a constant bit-rate (but not variable like we'd all want). I've seen a 9Mbit encoded signal, and it looks virtually the same as a high quality DVD.

Good point, which leads into one of my other questions about DVD recording technology: Can it record a 9Mbit per second stream on the fly, or will it have to cache to the hardrive? I honestly don't know, but could probably find out by looking at DVD-ROM specs I suppose.

Again, I'm not saying a consumer level DVD recorder is impossible, I'm just saying that it is not a trivial piece of equipment, and in my opinion will be too complex and too expensive to become mainstream.

I actually hope that these things do not become reality so as not to confuse the issue with current DVD players. I also hope the digital recording medium of choice is something along the lines of Replay TV / Tivo / or the Dish Network's Dishplayer, which I own.

As HD prices continue to drop, these things will have larger and larger capacities, and they could potentially support connections to external devices for permanent digital recording of their stored contents, eliminating the limitation of the fixed-capacity hard drive.

-Curt

[Sir Edmund]

I imagine the best way would be to record the entire program onto a harddrive. You could then burn it onto a recordable DVD if you decide you want to keep it permanently.

This would also allow you to do stuff like split the program over several discs, create menus and such.

Taking this idea a bit further, if the hard drive is big enough, you could store several hours of video on the hard drive, meaning several programs could be stored simultaneously. Then you'd just burn a DVD or two to make more room when needed.

It would have to be a pretty big harddrive, but they double in capacity every year anyway...

>Good point, which leads into one of my other
> questions about DVD recording technology:
>Can it record a 9Mbit per second stream on
>the fly, or will it have to cache to the
>hardrive?

Good question!

Since the higher end MPEG-2 encoders are hardware, all the compression takes place on the board. The hard drive just stores the finished signal. Of course, you need a pretty fast harddrive that runs at consistant speeds to avoid "hiccups".

But obviously a consumer DVD-Recorder isn't going to have a HD, as there really is no need. However, I wouldn't be surprised to see a consumer unit with a *huge* Cache onboard for the DVD burner.

Time will only tell. There is a new unit that was announced in Japan goes on sale next month that basically is a pseudo-DVD recorder unit. It uses a proprietary version of DVD-RAM, and can only be played on that unit.

THere was also an announcement of a DVD-RAM camcorder that will debut in 1st qtr of 2000, uses a 2 inch DVD-RAM disc.

These products show that recording on the fly can be done. But obviously there's more than meets the eye....

-Brian