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Why are DVD Recorders so much faster than PC's?

707 Views 5 Replies 4 Participants Last post by  Ollie W. Holmes
When I capture video on my PC, that takes the real time of that video (an hour for example), but then it has to encode and then burn an image to hard drive and then swrite chapeters and then burn to DVD which can take up to another 60-90 minutes even on a new computer.

What do the stand alone recorders do differently? Mine doesn't have a hard drive, I know that, but it must be decoding in real time. I don't know all the steps intimately, but it seems to me that from start to finish I can copy a tape in nearly 1/3 of the time it takes on a PC, and I wonder why that is. Are we sacrificing anything on the standalone besides precision editiing?

Thanks in advance.
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The magic is in the MPEG2 compression engine, built into the hardware on the standalone recorders. It enables you to put video data in one end and get MPEG2-compressed data suitable for writing onto a DVD disc out the other end, with no CPU computation required. The CPU in the unit only has to concern itself with running the user interface and controlling the DVD drive.

You can get MPEG2 capture cards for PCs that will do just this, as well as accelerate other MPEG2 conversion functions, but the ones with quality equivilent to the standalone recoders are often over $1,000. There are some low-budget ones I've tried, but I've found their quality to be lacking.

There may be some quality sacrifice on the standalone recoders in that since the MPEG2 compression is done in hardware in real time, there are limits as to how deep an analysis it can do to generate intermediate and predicted frames. On a PC with software conversion, you can optimize these settings, but you also can spend hours or days doing the compression.
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Because a PC is not geared to do mpeg-2 encoding in real time. Operations that would be done using parallel/vector processing on ASICs, must be done serially, using a general purpose instruction set for the Intel Pentium. Also, consider the O/S overhead of Windows XP, 2K or ME. Also there are very few good assembly language programmers around to take advantage of the speed and vectorizing capabilities of the latest P5 or Itanium chips.

A comparable benchmark would be to time a Pentium doing z-buffering and shading vs. doing the same graphics operation on an ATI or Nvidia adapter (with their 64 and 128 bit busses). Dedicated hardware is nearly always faster than microprocessors if the task can be simply described. However, if the algorithm requires a certain degree of decision making, then a dsp chip or risc chip would be the preferred route.

Except for multipass processing, I can think of no advantage a PC could offer in terms of pq encoding improvement, at least for analog capture. Certainly, the 3D Y/C is nowhere as good on the Pinnacle capture cards vs the Panasonic dvd recorders. Whether a PC could do a better job with mini-dv or dvcam data vs the Panasonic E100 is open to debate. Does anyone know if it has been tested in any magazine?
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You can do real-time MPG2 compression on PCs with the right hardware/software. I use an ATI All-In-Wonder Radeon TV tuner/capture card and ATI has software (Multimedia center) that you can do everything the standalone hard-disk recorders do. You can schedule timer recordings and it can record in MPG2 format with a bit rate you can customize. You could then use DVD authoring software if you wish to later put it on a DVD-R or RW. However the "slow" off-line encoders are much higher quality than the real-time encoders on PCs or standalone DVD recorders, they can do multipass operations and improve the quality with lower bitrate. You can get as good or better quality with 6hour mode with a good offline encoder than 1hour mode on a standalone. At least you have a choice on a PC to do either.

Can you give us an example of some "slow" off-line encoders that you would recommend?

Tmpgenc and CCE are good.

If you can get your data into vob format, even InstantCopy is acceptable for shaving 25% off the video file size.
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