MPEG 2 (DVD) decoding - Software vs. Hardware

Discussion in 'Computers' started by MarkHastings, Feb 26, 2004.

  1. MarkHastings

    MarkHastings Executive Producer

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    Can anyone explain this in more detail? I understand (to a certain point) that the hardware decoders are better because they don't require resources like the software decoders, but how can you tell if you have software or hardware decoding?

    Is the hardware decoder built into the DVD drive?

    The reason I bring this up is because a co-worker burned a constant 8Mb/sec DVD and my client is saying that the video is chocking. She has a DVD with a varible bit rate of 5.5-8Mb/sec video and that has no problems at all.

    It definitely sounded like she had software decoding because we suggested she disconnect from the network (to free up some resources) and the disc played fine after that.

    I told my co-worker to stick to around 6Mb/sec for any new DVD's he makes...does that sound fair enough to be compatible with software decoders?

    Anyways, I was just interested in knowing more about the differences between hardware and software in detail.
     
  2. Scott L

    Scott L Producer

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    6mb/sec sounds like quite a lot, or maybe I'm just used to encoding material at 4mbps Xvid. Simple answer is if it's Win2k or XP just press ctrl+alt+del and see if WinDVD or PowerDVD is bogging down the CPU.

    It may be a bandwidth problem getting all the data to the CPU. Make sure her HD and DVD aren't on the same IDE channel (put them on seperate ribbons).
     
  3. Ken Chan

    Ken Chan Producer

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    The hardware decoder is usually part of the video card (any nVidia or ATI has had it for a while); the drive just reads bits of the disc. The primary resource that is consumed with software decoding is CPU time. A sufficiently fast general purpose CPU could be faster than dedicated hardware. Just ballparking, but a 2GHz Pentium 4 isn't there yet, you might use 30%(?) CPU playing a DVD. So not a lot, but not a little. How fast is the computer in question? I always run the Task Manager minimized so that I see the CPU meter in the tray.

    Aside from noticing that the DVD player program is using a whole lot of CPU playing the DVD, the program might have a diagnostic screen and/or actual UI allowing the user to choose hardware decoding. PowerDVD definitely has it.

    The data rate for a DVD is about 11Mbit/s, which is really quite low for modern systems. So I'm guessing it's not simply the IDE channels or the bus. If disconnecting from the network fixes the problem, that's bad in an overall sense, because simply being connected to the network without doing anything shouldn't really consume many "resources".

    6Mbit/s VBR is probably in the "typical" range for DVD. I haven't really tried software decoding on older systems, so I can't say whether that's a good number. It seems like a shame to reduce the quality just so that the discs play on underpowered computers, especially when a standalone DVD player that can handle any disc is so cheap.
     
  4. MarkHastings

    MarkHastings Executive Producer

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    Thanks for the responses guys. I'm not in the IT department, so I didn't talk to the client directly, but I was offering my advice because it sounded like a decoding issue rather than a DVD issue (which was what IT was thinking it was).

    If they ask me for more help, I'll try to get specs, but I'm not too worried about it. I just wanted to know all that I can about it so I can help out more if needed.

    Thanks again.Yeah, but who knows what the client had running as well, maybe disconnecting was enough to free up the little bit of resourcing the decoder needed?
     
  5. Scott L

    Scott L Producer

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    I'm thinking the network is constantly checking or pulling up files from the Harddrive, and if it's on the same channel as the DVD-ROM you'll get problems.
     
  6. MarkHastings

    MarkHastings Executive Producer

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    I just noticed that I forgot to mention the client had a laptop, which would explain the need for every last bit of available resources.
     
  7. Ken Chan

    Ken Chan Producer

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    Well, I guess that would depend on the laptop. The high-end ones nowadays should have no problem. And sure, if you're actually doing something with the network, that could cause bog things down, but if you're just "connected"? But who knows... that's what makes working with computers so interesting.
     
  8. Steve Berger

    Steve Berger Supporting Actor

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    Sorry to butt in here but I don't think that hadware vs software decoding is the issue here. Her drive probably can't spin fast enough to play an 8mbit/s CBR recording. The DVD standards are , I believe , for a maximum of 8-9mbit/s with VBR and usually an average around 4mbit/s and I don't know of any standalone DVD players that could handle an 11mbit/s recording. A 16X DVDRom drive might play it but a 3-5X would probably choke on it. For compatibiliy you really shouldn't go over 4mbit/s average and 6mbit/s maximum (a burned disk is harder to read that a commercially pressed disk).

    A hardware decoder is something like an Xcard or Hollywood Plus (there were some Quadrant cards also) . Video cards can do hardware assist at best and even that often requires tweaking. But even at that a 700-800Mhz processor can usually do software decoding without a glitch --- if the drive can keep up and the filters are any good. (directshow filters are usually used for playback decoding)
     
  9. Ken Chan

    Ken Chan Producer

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    That's the data rate, not the video bitrate. 11 is a 1x DVD-ROM. The fact that the DVD does play -- although only when not connected to the network -- would indicate the drive is fast enough, at least then.
     
  10. DaveB

    DaveB Stunt Coordinator

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    I can confirm what Steve Berger said above from my own experience.

    I installed a dedicated MPEG2 decoder card along with my first DVD-ROM drive about 4 years ago. In spite of the fact that the hardware decoder was supposedly the best on the market at the time, I felt the quality was lackluster. I removed the card and began using a software decoder and the improvement in quality was considerable.

    I was using PowerDVD with a Pioneer 16X DVD-ROM on a P3 733Mhz.

    Also, as was mentioned, many video cards will do a CPU assist which can carry up to 20% of the CPU load for DVD decoding. If you have a fast CPU you likely won't notice any difference.

    David
     
  11. MarkHastings

    MarkHastings Executive Producer

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    I didn't even consider drive speed.
     

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