2-hour length, 148.50 Mhz, 1920 x 1080 progressive scan image, 1-bit object data, 193 bits of file s

Discussion in 'Windows Media Player' started by Radium, Oct 27, 2006.

  1. None of the "original bits" is left. A compressor takes in a data
    stream and generates a new, smaller, data stream that can be decoded to
    some approximation of the original image or video sequence.

    The bit rate of the compressed data stream is simply the number of bits
    per unit time (frame, second, hour, whatever you prefer) divided by the
    number of original pixels in that same time period.

    Dave
     
    Dave Martindale, Oct 31, 2006
    #41
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  2. Radium

    Pasi Ojala Guest

    If you have some kind of predictor coding, one input bit is
    capable of much more than monochrome.

    And, one bit per pixel _on average_ is capable of much more
    still. Ever heard of arithmetic coding?

    -Pasi
     
    Pasi Ojala, Oct 31, 2006
    #42
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  3. Radium

    Pasi Ojala Guest

    If you have some kind of predictor coding, one input bit is
    capable of much more than monochrome.

    And, one bit per pixel _on average_ is capable of much more
    still. Ever heard of arithmetic coding?

    -Pasi
     
    Pasi Ojala, Oct 31, 2006
    #43
  4. Radium

    Bob Myers Guest

    No, let's try this another way.

    Let's say you have an original video stream that consists
    of - gee, I don't know - let's say 1920 x 1080 pixel
    frames that come at you at a rate of 30 per second.

    That would be 1920 x 1080 x 30 pixels per second, right?

    Working out the above, we could say it's 62.2 million pixels
    per second.

    Now let's say that we compress this into a data stream which
    has an average rate of - again, just to pick a number completely
    at random - 19.39 Mbits/second.

    On average, how many bits per pixel of the original
    video stream does that compressed stream give you?

    Bob M.
     
    Bob Myers, Oct 31, 2006
    #44
  5. Radium

    Bob Myers Guest

    No, let's try this another way.

    Let's say you have an original video stream that consists
    of - gee, I don't know - let's say 1920 x 1080 pixel
    frames that come at you at a rate of 30 per second.

    That would be 1920 x 1080 x 30 pixels per second, right?

    Working out the above, we could say it's 62.2 million pixels
    per second.

    Now let's say that we compress this into a data stream which
    has an average rate of - again, just to pick a number completely
    at random - 19.39 Mbits/second.

    On average, how many bits per pixel of the original
    video stream does that compressed stream give you?

    Bob M.
     
    Bob Myers, Oct 31, 2006
    #45
  6. Radium

    Bob Myers Guest

    Doesn't matter. Again, the compressed stream is delivering data
    at a rate which, relative to the original pixel rate, represents less
    than one bit per pixel on average.

    Now, it turns out that the numbers I picked in my example were
    not (surprise, surprise!) chosen completely at random:

    19.39 Mbit/sec is the actual data rate limit specified in the ATSC
    (U.S. digital/HD TV) broadcast transmission standard.

    1920 x 1080 at 30 frames/second, is, of course, a standard HD
    format and frame rate. As it happens, such material is generally
    originated as RGB data at at least 8 bits/color (24 bits/pixel);
    long before getting to the compressed form of the final data
    stream, it will most likely be re-encoded as YCbCr at something
    less than a 4:4:4 sampling scheme - probably 4:2:2 or even 4:2:0
    (which are systems that effectively reduce the spatial resolution
    of the color components, while preserving the luminance component
    at full resolution - this is itself a form of lossy compression vs. the
    original RGB representation). The result then goes through a goodly
    number of further compression processes, which results in the
    cumulative data-rate reduction (compression ratio) seen in the end
    result - something in the neighborhood of 80:1 vs. the original.

    Bob M.
     
    Bob Myers, Nov 1, 2006
    #46
  7. Radium

    Bob Myers Guest

    Doesn't matter. Again, the compressed stream is delivering data
    at a rate which, relative to the original pixel rate, represents less
    than one bit per pixel on average.

    Now, it turns out that the numbers I picked in my example were
    not (surprise, surprise!) chosen completely at random:

    19.39 Mbit/sec is the actual data rate limit specified in the ATSC
    (U.S. digital/HD TV) broadcast transmission standard.

    1920 x 1080 at 30 frames/second, is, of course, a standard HD
    format and frame rate. As it happens, such material is generally
    originated as RGB data at at least 8 bits/color (24 bits/pixel);
    long before getting to the compressed form of the final data
    stream, it will most likely be re-encoded as YCbCr at something
    less than a 4:4:4 sampling scheme - probably 4:2:2 or even 4:2:0
    (which are systems that effectively reduce the spatial resolution
    of the color components, while preserving the luminance component
    at full resolution - this is itself a form of lossy compression vs. the
    original RGB representation). The result then goes through a goodly
    number of further compression processes, which results in the
    cumulative data-rate reduction (compression ratio) seen in the end
    result - something in the neighborhood of 80:1 vs. the original.

    Bob M.
     
    Bob Myers, Nov 1, 2006
    #47
  8. Radium

    Bob Myers Guest

    If you look back through the thread, you'll see that I've
    been contributing rather regularly - and as has been
    said several times before, by myself and others, there
    have to be a LOT more than just one bit. Or even one
    bit per second.

    Bob M.
     
    Bob Myers, Nov 2, 2006
    #48
  9. Radium

    Bob Myers Guest

    If you look back through the thread, you'll see that I've
    been contributing rather regularly - and as has been
    said several times before, by myself and others, there
    have to be a LOT more than just one bit. Or even one
    bit per second.

    Bob M.
     
    Bob Myers, Nov 2, 2006
    #49
  10. Can anybody explain what is the point of this whole
    "discussion"? It seems to me like one of the most
    ridiculous wastes of time that has come along here
    in months/years.
     
    Richard Crowley, Nov 2, 2006
    #50
  11. Can anybody explain what is the point of this whole
    "discussion"? It seems to me like one of the most
    ridiculous wastes of time that has come along here
    in months/years.
     
    Richard Crowley, Nov 2, 2006
    #51
  12. Radium

    Pasi Ojala Guest

    When someone else is doing video compression (btw, it not
    AN image, video compression handles multiple images), it is
    much more than that.

    There's delta coding (differences between frames), transform coding
    (for example DCT) and quantization (represent data that matters most
    more accurately). And/or prediction and encoding only prediction error.

    After this lossy phase you use lossless entropy codes.

    -Pasi
     
    Pasi Ojala, Nov 2, 2006
    #52
  13. Radium

    Pasi Ojala Guest

    When someone else is doing video compression (btw, it not
    AN image, video compression handles multiple images), it is
    much more than that.

    There's delta coding (differences between frames), transform coding
    (for example DCT) and quantization (represent data that matters most
    more accurately). And/or prediction and encoding only prediction error.

    After this lossy phase you use lossless entropy codes.

    -Pasi
     
    Pasi Ojala, Nov 2, 2006
    #53
  14. Radium

    Bob Myers Guest

    Doesn't matter whether you talk about bits, bytes, words,
    characters, or squamishes (a word I just stole from an old
    Mad magazine to refer to data organized in 43-bit chunks).
    You start out with this many bits, you wind up with this many
    bits. It's just that "average bits per displayed pixel" has been
    one of those fun ways of presenting compression ratio
    information, especially in seminars where the objective of
    the presenter is to elicit a "wow!" response from the audience
    which is presumably learning about this stuff for the first time.

    And you're never simply throwing away bits or bytes in
    any practical compression scheme which is currently in
    use; that would be far too crude. What happens in real-
    world systems is far more complicated, and produces a
    far better result.

    Bob M.
     
    Bob Myers, Nov 2, 2006
    #54
  15. Radium

    Bob Myers Guest

    Doesn't matter whether you talk about bits, bytes, words,
    characters, or squamishes (a word I just stole from an old
    Mad magazine to refer to data organized in 43-bit chunks).
    You start out with this many bits, you wind up with this many
    bits. It's just that "average bits per displayed pixel" has been
    one of those fun ways of presenting compression ratio
    information, especially in seminars where the objective of
    the presenter is to elicit a "wow!" response from the audience
    which is presumably learning about this stuff for the first time.

    And you're never simply throwing away bits or bytes in
    any practical compression scheme which is currently in
    use; that would be far too crude. What happens in real-
    world systems is far more complicated, and produces a
    far better result.

    Bob M.
     
    Bob Myers, Nov 2, 2006
    #55
  16. Not at all - have a while on rec.video.production, the long rambling
    threads which continually descend into flame wars and pointless abuse
    rants makes these groups look like a walk in the park !

    At least Radium sticks to the same name when trolling - but
    PLEASE DO NOT FEED THE TROLL !

    Thankyou !
    Cheers - Neil
     
    Neil Smith [MVP Digital Media], Nov 2, 2006
    #56
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