Determining PCM space requirements

Discussion in 'Archived Threads 2001-2004' started by John_Berger, Jul 15, 2002.

  1. John_Berger

    John_Berger Cinematographer

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    Okay. Another question for everyone. (I'm just full them them lately -- questions, that is. [​IMG] )
    I attempted to create a DVD of my one friend's wedding over the weekend. The software that I use handles PCM audio or Dolby Digial 2.0.
    Obviously, DD 2.0 is great for compression and arguably for overall quality of the audio; however, it prevents the use of Dolby ProLogic to try to get a pseudo-surround channel. (At least, it prevents it on my receiver.)
    So, when I created the DVD project (fortunately I did it to the hard drive, not directly to a disc) and selected PCM, the entire project ended up being 5.3 GB which is too much. Just to give a little background, the MPEG-2 files that I used were about 4.1 GB total w/ 192 KHz audio. I based the video and audio bit rates using a bit rate calculator that I downloaded. Unfortunately, the calculator assumes MP2 audio compression with no option for PCM. So if I retained DD 2.0 w/ 192 bit rate, everything fit. By exploding the compressed audio back to PCM, the project was just too big.
    So, my question is this. Unless video quality is imperative or the DVD is to be monaural, I would prefer to use PCM at this point. Should I assume that the audio space requirements will be like regular audio CDs of 650 MB per ~70 minutes -- or just to give me some breathing room allocate 10 MB per minute -- and then determine the video bit rate from there? Is the mathematical solution that simple?
    Advice will be appreciated.
     
  2. Steven K

    Steven K Supporting Actor

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    Remember this about Redbook audio CD PCM... it is sampled at 44.1 KHz (44,100 times per second) at 16-bits per sample. Reducing either the frequency or the resolution will yield smaller audio files, albiet audio of lesser quality.
     
  3. Jeff Kleist

    Jeff Kleist Executive Producer

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    I can force Pro-Logic on my reciever, you just have to specifically activate it. Check and see if your authoring software will allow you to flag it as pro-logic
     
  4. Ken Chan

    Ken Chan Producer

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    If you have a decent Dolby Digital encoder, you should be able to specify a 2.0 sountrack:
    - Is Dolby Surround
    - Is NOT Dolby Surround
    - No declaration one way or the other
    Also, unless you actually recorded in surround sound and matrixed it into two channels, you generally don't want to playback the audio with ProLogic, which would only give you fake surround. So if for example, you're making personal copies of your favorite TV show, which is Dolby Surround encoded, you'd turn it on. But if you recorded stuff with your camcorder, which is just plain stereo, you'd turn it off.
    DVD allows several different bit rates and depths for PCM, but you probably used (or your low-end authoring program will convert to) [email protected] (a little higher than CD), so:
    48000 * 16 * 2 channels / 1024 = 1500kbps
    If you can type in 1500 (instead of 192) in the bitrate calculator, you're all set.
    FYI, the amount of time you get on a CD is misleading because the block sizes for audio CDs (which have no error correction) are larger than CD-ROM (which do). If you took an audio CD that was filled to the max, copied the audio into WAV files, and tried to burn a data CD with those files, they would not fit.
    //Ken
     
  5. John_Berger

    John_Berger Cinematographer

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  6. Ken Chan

    Ken Chan Producer

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  7. John_Berger

    John_Berger Cinematographer

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    Not impressed with it. I think I'd rather do Perl anyway which at least is cross-platform.
     
  8. Ken Chan

    Ken Chan Producer

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  9. Wayne Bundrick

    Wayne Bundrick Cinematographer

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    Ken is right. Receivers are supposed to be able to apply ProLogic processing to any stereo source, even a Dolby Digital 2.0 signal.

    Anyway, stereo PCM on DVD is 1,536,000 bits per second so you need to factor 1.536 Mbps into your calculations. The maximum video rate is going to be about 8 Mbps (since video + audio can't exceed 10 Mbps), and PCM takes about 11.5 million bytes of space per minute.
     
  10. John_Berger

    John_Berger Cinematographer

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  11. Wayne Bundrick

    Wayne Bundrick Cinematographer

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    Yeah, it's a DVD restriction. The DVD standard is based on what was practical, readily available, and inexpensive back in 1997.
     

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