DVD Data Rates and Quality?

Discussion in 'Computers' started by MarkHastings, Aug 2, 2004.

  1. MarkHastings

    MarkHastings Executive Producer

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    Can anyone equate DVD Data rates to video quality?

    Example, here are some formulas I created using the default settings in Adobe's Main Concept MPEG2 encoder:


    High Quality
    -Video: Max: 8000 Kb/sec / Average: 6000 Kb/sec

    Medium Quality
    -Video: Max: 6000 Kb/sec / Average: 4200 Kb/sec

    Low Quality
    -Video: Max: 4500 Kb/sec / Average: 3200 Kb/sec


    since I needed a format to get 90 minutes onto a DVD (the high quality only gave me 80 minutes after factoring in PCM audio), I created a Med-High quality:

    Medium-High Quality
    -Video: Max: 7000 Kb/sec / Average: 5200 Kb/sec


    The question is, at what data rate does the video quality start resembling VHS quality? The high quality looks great and I assume my Med-High quality is also great, but is the Medium quality still better than VHS? If I remember, I thought someone said that the Med. quality data rate was like S-VHS quality.

    Obviously the low quality is VHS and less quality, but how do you feel about the Medium quality? Is that too low for DVD qulaity?

    p.s. I am not using audio compression (i.e. no Dolby Digital audio), so I am running:
    Audio: 11 MB/sec (16 bit / 48 kHz / stereo)
     
  2. Christ Reynolds

    Christ Reynolds Producer

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    i'm not sure about the data rates -> video quality, but maybe you can try to make a bunch of samples of the same clip, then vary the video quality from good to bad, or vice versa. put those on a dvd rw, then you can let your eyes be a judge for your particular project.

    CJ
     
  3. Scott L

    Scott L Producer

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    The best way is to find out for yourself, make a couple of small encodes for key scenes and compare.

    4mb/sec is still better than VHS quality but it can still depend on the encoder. Are there settings for fast vs. quality?

    edit- Ah I see it's max and average. I think Medium quality has decent figures, but if your med-high profile fits the bill why not choose it?
     
  4. MarkHastings

    MarkHastings Executive Producer

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    I'm definitely going to do that to show my boss so she can see the difference. I just wish I could explain to a client (over the phone) just what they are getting with something like "Medium" quality.

    Thanks for the suggestions, I guess I'll just have to show the client (in person) what the Medium quality is like.
     
  5. Ken Chan

    Ken Chan Producer

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    Why not encode to Dolby Digital? Uncompressed PCM takes up a lot of space.
     
  6. MarkHastings

    MarkHastings Executive Producer

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    I don't want to have the authoring app do any re-encoding, so I want to leave that up to the "real-time" capturing. It uses the Main Concept compressor, which has MPEG layer 2 as an audio codec...I assume that translates into Dolby Digital on a DVD player?

    If I go with the highest MPEG-2 audio codec, I get 3 MB/sec, which allows 93 minutes of the high quality video.

    I'm going to test out a few of the compression schemes on my HT. I've never been fond of the audio compression schemes with these types of apps, but maybe this one will sound better since I am using a higher end system.
     
  7. Ken Chan

    Ken Chan Producer

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    First, NTSC DVD players are not required to support MPEG audio, although a lot of them do. (If the player also plays MP3 CDs, then it almost certainly does.)

    If it does support MPEG audio for DVD, it may have the option to pass the bitstream unchanged (as with DD or DTS), or more likely it will decode it into PCM. Of course, having been compressed, you've lost some quality. That PCM will go out as a digital bitstream, or be converted to analog with the player's DAC, just as Dolby Digital would have. But it never converts MPEG audio to Dolby Digital.
     
  8. Keith Paynter

    Keith Paynter Screenwriter

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    What application are you using? Does it require DVD menus?

    Adobe Premiere Pro has a great way to tell you how you're using space in creating menu-less DVD's. When you decide the video encoding rate (using a variable bitrate estimate or a constant bitrate setting) the disc authoring menu lets you see how much of the available 4.38GB you've under-used (or overused for that matter) before you start burning. The stock audio encoding is PCM stereo, but for (ugh!) $300 US you can get a SurCode 5.1(!!) DD plug-in.

    I've made 90 min DVD's (such as the Moroeder Metropolis LD) at approx 6.0 CBR and looks great.

    Using Adobe Encore DVD I was able to transfer my Criterion Spinal Tap LD and get all 3 soundtracks (Film/cast/crew commmentaries) without any menus. The audio took up only 500MB of data with DD surround encoding.
     
  9. MarkHastings

    MarkHastings Executive Producer

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    I'm using Abode Encore for authoring. I am using a Digital Rapids capturing system to capture the MPEG2 clips in real-time, so I am trying to avoid re-encoding with the DVD authoring app.

    I believe Encore will allow me to re-encode the PCM into DD, but I'd rather not go that method, but if I have to, I have to.When I tried to burn the DVD, the app said something about non-standard audio. I guess I'll have to stick with PCM and have Encore do the re-encoding.
     
  10. Keith Paynter

    Keith Paynter Screenwriter

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    I'm almost exclusively recording with Premiere Pro, using a firewire capture from a JVC GR-D74U mini DV camcorder - ideal for transferring analogue sources (non-Macrovision VHS or LD) direct via A/V input - no tape dubbing required.

    Right now I'm porting the Apocalypse Now doc "Hearts Of Darkness". The raw 96 minute film capture required approx 22GB of data, and after editing in Premiere (trimming side break, another 21GB written at 1:1 against original time), I'm converting via Encore. I've squeezed it into approx 4.27GB for DVD at around 5.25 CBR with DD audio at 320Kb. On a P4/1.6 it's taking me about 8 hrs to transcode and write (a good overnight project).
     
  11. Ken Chan

    Ken Chan Producer

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    Maybe there is an option in Encore to disable this. Or perhaps you can use another app, maybe TMPGEnc or DVD-lab, to create non-standard discs. If the clients understand that the discs are non-standard, but it will make it easier/cheaper....
     

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