How much space do Dolby 2.0 tracks consume?

Discussion in 'Archived Threads 2001-2004' started by Ricardo C, Oct 8, 2002.

  1. Ricardo C

    Ricardo C Producer

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    The reason I'm asking is this: When I purchased my FOTR disc, I got the NTSC R4 Latin American release, so I could have Spanish subtitles (useful when guests don't speak English). Well, in addition to the subs, the disc contains a Spanish 2.0 track, a Portuguese 2.0 track, and an English 5.1 track. Is there any chance the PQ of my R4 disc suffers in comparison to the English-only R1 release? Should I get the R1 release in order to have the best possible visual quality?
     
  2. Craig W

    Craig W Second Unit

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    It's not necessarily disc space, but rather the bandwidth available in the DVD bitstream. 2.0 tracks are really quite small compared to what the disc is capable of holding.
    The bandwidth is a real concern. Each 5.1 track takes 448 or 384kbps of that bandwidth. Each 2.0 track typically takes 192kbps.

    Although if a disc just has one 5.1 track and a two or three 2.0 tracks thats only occupying about 10% of the bandwidth. I would suspect that the same video files generated for region 1 were the same for the other releases. Why compress it twice when once will suffice? So I don't think you are going to get a noticeable improvement if they are from different compression sessions. I would be more worried if a disc was loaded with more than three 5.1 tracks in addition to multiple 2.0 tracks.
     
  3. Robert Spalding

    Robert Spalding Second Unit

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    i noticed a movie like Evolution had 3 5.1 tracks and 2 2.0 tracks. plus 3 subtitle tracks.
     
  4. MikeEckman

    MikeEckman Screenwriter

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    Heres a good way to approximate how much disc space a certain track takes up. Take the bitrate (192 for 2.0, 384 or 448 for Dolby 5.1, 754 for half rate dts, etc) and input it into the following formula:

    x = bitrate
    y = length of movie in minutes

    x * 1024 / 8 * 60 * y / 1,048,576 = Space in Megabytes Used for that Audio track.

    So, lets say, you want to find out how much space a Dolby 2.0 track takes up on a 90 minute movie....

    192 * 1024 = 196608 bits per second
    196608 / 8 = 24576 bytes per second
    24576 * 60 = 1474560 bytes per minute
    1474560 * 90 = 132710400 bytes in 90 minutes
    132710400 / 1048576 = 126.56 Megabytes

    Figure a DVD-9 holds approx 8.4 Gig of data, which is approx 8602 Megabytes, and that Dolby 2.0 track takes up 1.471% of the total maximum disc space.

    A single 448kbps Dolby 5.1 track in a 90 minute movie takes up 295.31 MB, which is 3.433% of the disc space.

    A single 754kbps dts track in a 90 minute movie takes up 497.02 MB, which is 5.778% of the disc space.
     
  5. Michael St. Clair

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    I have a few anime and music titles that do 2.0 stereo at 448k.
    The sound is excellent, and approaches or matches regular PCM stereo.
    High bitrate stereo should be used for every film with an original stereo or dolby (matrixed) surround track.
     
  6. Alex Spindler

    Alex Spindler Producer

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    MikeEckman,
    It warms my heart to see people properly calculating kilobytes and Megabytes. I can't tell you how many times in technical publications where this is ignored.
    Good formula. [​IMG]
    Question: Do they further compress the stored audio file, or is it left in pure form on the DVD?
     
  7. MikeEckman

    MikeEckman Screenwriter

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  8. Ricardo C

    Ricardo C Producer

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    Thanks so much, everyone! [​IMG][​IMG]
     
  9. James Reader

    James Reader Screenwriter

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    Look at the number of soundtracks and subtitles on this R2 release:
    Bram Stoker's Dracula
    And yet the reviews state a stunning picture. Don't forget PAL movies have higher definition, and this require more space as well.
    I think you guys are worried about soundtracks too much, and subtitles take up hardly space. The quality of the encoding is what really matters.
     
  10. Michael St. Clair

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  11. James Reader

    James Reader Screenwriter

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    Well, that's another reason not to buy R2 titles, as the Dracula example above is not unsual.
     
  12. Brent Hutto

    Brent Hutto Supporting Actor

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    Michael St. Clair brings up a point I've been curious about. Let's say you've got a boatload of audio tracks eating into your bandwidth. So maybe there's only 7000kbps or so peak video bitrate available.

    It's my impression that you can filter the picture to the extent that it will comfortably fit into that 7000kpbs without any noticable compression artifacts but the entire picture will be soft and lacking in detail. Is it possible (practical) to make a tradeoff between that filtering of detail and the occasional pixellation on difficult scenes? By that I mean a parameter in the encoding process that sets the filtering level.

    If so, is it a parameter that is set globally for each movie or can it be adjusted on the fly? By that I mean could you leave lots of detail (less filtering) on easy-to-compress or less fast-moving scenes but then filter the heck out of the image for a few seconds whenever a hard-to-compress scene appears?

    Or do I fundamentally misunderstand the encoding process?

    One final question. If all you had was a single 2.0 audio track and no subtitles, could you have a peak video bitrate of, say, 9500kbps or so? Or is there some upper limit to the video bitrate separate from the 10000kbps limit of the DVD overall?
     
  13. Ken Chan

    Ken Chan Producer

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  14. Ricardo C

    Ricardo C Producer

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    James, I guess you are right [​IMG]
     
  15. Ricardo C

    Ricardo C Producer

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    Michael, does that mean I'll have to at least rent the R1 disc to know for sure?
     
  16. Michael St. Clair

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    Ricardo,

    I have been speaking in general terms.

    In the case of 'Fellowship', unless they screwed up I'd say the picture quality should be very, very close to the R1 release. One additional 2.0 track (drop the english 2.0 track, replace with 2 others) is just not that much (and the Portugese subs may be 'free' if they dropped the english subs). There are other releases where the soundtracks are getting crazy, but this release sounds fine to me.
     
  17. MikeEckman

    MikeEckman Screenwriter

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    Oh, just for the hell of it, I simplified the equation...

    To find out how much disc space a given bitrate track (x) takes up in a given length movie (y), do this:

    0.0073242 x y = Size in Megabytes of track.
     
  18. Nick_Scott

    Nick_Scott Second Unit

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    Brent-
    I don't know about the high-quality studio encoders, but the cheap ones have "global" filters and edge enhancers.
    For an example from TMPG (a free DVD encoder):
    [​IMG]
    Like wise, for edge enhancement:
    [​IMG]
    So, at least for the cheap ones, it looks like you only have 2 choice: on or off:
    [​IMG]
    My guess is that the better studio encoders probobly do have some sort of variable filters. I remember Bjoern saying that Star Wars had "adaptive" filters/enhancments.
    Actually, I'm tempted to take the nice-looking trailer from StarWars-1 DVD, and try to make it look like regular scenes by adjusting the above settings....
     
  19. Alex Spindler

    Alex Spindler Producer

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    Perhaps I'm not thinking clearly, but I didn't think that all of the audio channels were extracted from the DVD while playing. My impression was that you selected the audio stream you would be listening to and it would access that off of the disc. The other audio tracks were in separate files that would not be read.

    Or is the audio file one large file that must be entirely read while any audio track is playing, from the lowest 2.0 to the highest bitrate DTS?

    If it is the former, I wouldn't see how multiple audio tracks would exhaust the bandwidth of the DVD player.
     
  20. Nick_Scott

    Nick_Scott Second Unit

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    Alex-
    Yes, it is one big file- Including subtitles, and alternative angles. That is why many here are against including a DTS track since it chews into the bitrate for the video. Personally, I liked it when DTS when separate full-bitrate releases, but those days are long gone.

    On a side note, I have only seen 5 minutes of "who wants to be a millionare"... the only question I saw was:
    How many bytes in a Kilobyte... and they said the answer was 1000!
     

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