aspect ratio not quite right

Discussion in 'Amateur Video Production' started by Irwin Feuerstein, Dec 22, 2003.

  1. I am not getting the correct aspect ratio out of tmpgenc. Here is what

    I take a movie in AVI format. AVIcodec says it is DivX v3, resolution
    544 x 288, and aspect ratio 16:9. I want to make a VCD out of it. So I
    load it into tmpgenc, tell it that the source is 16:9 (why doesn't
    tmpgpec know that by itself?). It automatically chooses a 4:3 output
    which can't be changed. In output, I tried both full screen (keep
    aspect ratio) and no margin (keep aspect ratio), and the results are
    the same. Both give mpg results that are close, but playing them in
    media player or windvd both show output that are a little too tall for
    the width when put up side by side with the original.

    Why is it not preserving the visual aspect ratio?

    Irwin Feuerstein, Dec 22, 2003
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  2. I hope I can help you with this.....

    The aspect of 1:1, 4:3, and 16:9 are really what you intend it to be played
    back on. The output should be 4:3, because that's all the VCD format
    allows, even if you have a widescreen TV, 16:9. I always leave the input as
    the same as the output. Generally, this is goign to be 4:3. 16:9 should
    only be used for DVD production, and at that, anamorphic DVD production.
    Since none of your AVI sources are anamorphic, I've never had to make a 16:9
    DVD. I imagine though, if you had a 16:9 TV, you might have to do something
    to it so that it plays correctly, but this may well just be a player issue
    as well.

    Anyways, since you are using VCD, you need to select the output as 4:3. The
    input I also choose to be the same as the input, this prevents TMPGEnc from
    resizing it, even if you think your aspect is 16:9.

    This is how I do it, however:

    For VCD, (I assume you are in the US like me), I need to use NTSC standards,
    so I make a custom project, choose MPEG-1, and if the frame rate of the
    video is 23.967, then I use that, if it is 29.97, then I use that, if it is
    25 then it was originally PAL, and you need to choose 23.967, and then in
    the advanced options "do not frame rate convert," this will make your video
    play longer than it is really [for 100:00.00min, it is now 104:18.60, not
    really noticeable]. I set the output as '4:3 display', and the input as
    '4:3 display'. The size is 352x240. Rate control is CBR, 1150kbps.

    For advanced, the Video Arrange Method is Center (Custom Size).

    This is where the real part comes in. The input here is 544x288, and the
    output is 352x240, but to not resize it the video needs to be something else
    since the two aspects are different (1.888:1 vs. 1.466:1). So, I take some
    basic math, ratios... 544/288 = 352/Y. Therefore, you cross multiply to
    find that 544Y = (352x288), therefore Y = 186. So you want to make the
    video arrange to be center (custom size) 352x186.

    Here's another tip, TVs have overscan. To make your whole video play in the
    TV screen, for the VIDEO ARRANGE CENTER (CUSTOM SIZE) use a 336xY value. To
    find Y, here, we do like before, so 544/288 = 336/Y. Now we have Y = 177.
    So to make the whole thing fit on your TV, use 336x177 for video arrange.

    The good part about using the overscan idea is that you have more black
    space. This means more of the 1150kbps can be allocated to the picture,
    thus imporving the picture.

    If you ever get the urge to make some SVCDs, though, you'll need to do
    something similar. SVCD is different from VCD in that instead of MPEG-1,
    you choose MPEG-2. If your source was 23.967, then you need to change
    Encode Method to 3:2 on playback, and you'll notice the frame rate changed
    to 23.967 (internally 29.97). If it is 29.97, fine, leave it, but on encode
    method you should pick interlace, since TVs are interlaced. The output and
    input aspects should be 4:3 (display). For rate control you can either do
    Manual VBR, or 2-pass VBR. Manual VBR specifies a max bitrate, I use
    2420kbps for max. It also has a minimum, some DVD players will get hung up
    if there isn't enough data, so if you know that value, you can specify it,
    or if you have a non-picky player, choose something, I use 750 for a
    minimum. In 2-pass it is the same thing, except now you have an average
    bitrate to specify. If you know how long your thing is and you want it to
    be 1 cd, then you have to do some math to find that average.

    The math for the average bitrate is pretty easy. You have an 80min CD-R,
    and say, 60 minutes of video. It has audio, so you need to leave off
    224kbps for audio from the final answer you get here. An 80 min CD-R holds
    800MB of MPEG-1/2 VCD/SVCD data, it is special, so knowing this you take the
    800MB, which is 6,553,600kb, and the length which is 60 minutes or 3600
    seconds, and divide, so you get 6,553,600kb/3600s = 1,820kb/s. Now take off
    224, so you have an average of 1596 for the video. That won't look too
    good, but oh well...

    Now, the SVCD has a size of 480x480, so put that in. For advanced, you
    really only want the input to be "4:3 display" and to have the Video arrange
    method center (custom size). Like before, I use ratios, so:

    544/288 = 480/y **It is important to note here, that this "y" is 75% of
    the actual Y you want**
    y = (480x288)/544
    y = 254

    The Y you want though is 4/3 of this y, so multiply by 4/3 (this is because
    of the way SVCD plays on TVs...due to their 4:3 aspect),
    Y = 338.

    Now, remember that overscan thing. Well, that 336/352 is 95.45% of the
    horizontal, so we can multiply 480 x 95.45% = 460 (approx; actually about
    459, but 460 works just as well).

    So, now you have to find how big it is based on a 460px wide video.

    544/288 = 460/y (again, it is 75% of the actual value)
    y = (460x288)/544
    y = 244

    Y = 325

    It is important to remind you of the difference between SVCD & CVD (not
    really much of a standard, since it is SVCD but with 1 change). CVD is
    352x480, while SVCD is 480x480. CVD's 480px height will use the SAME "Y" as
    you derived from the above calculations, which is interesting to say the
    least. So, basically, CVD is SVCD but instead of using a 480px video width
    (on the main page), you use 352. The height for the video ARRANGE is the
    same as it would be if it were 480px wide. If you want to do the overscan
    thing, the ARRANGE width is 336, but the height is what it would be as if
    there was a 460px width. Everything else is the same. CVD in theory can
    have less blockiness and artifacts, but SVCD has more resolution, so it is a
    balance of what you want.
    Anonymous Joe, Dec 22, 2003
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  3. Irwin Feuerstein

    Samuel Paik Guest

    The AVI file format doesn't have aspect ratio information. Specific
    video codecs may embed aspect ratio information into the video stream,
    but a general AVI file reader won't know about it.
    I believe VideoCD is always 4:3
    How does it look in a real VideoCD player?
    Samuel Paik, Dec 23, 2003
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