Alarmed by QuickTime's bitrates from H.264 presets

Discussion in 'Digital Video' started by rawdawg, Oct 1, 2009.

  1. rawdawg macrumors 6502

    Jan 7, 2009
    I use QuickTime to export H.264 very often. By default when you select Options > (Video) Settings the Compressor Quality is set to "High". I always figured that was sufficient. But I did a little test to determine what bitrates Quicktime is selecting and am very surprised!

    The test footage came from at short section ripped from a DVD using MPEG Streamclip. It was 47MB and 27 sec long.

    I tried the Automatic Presets for H.264 from Low to Best. Here are the results:

    Data Size - 923.41 K
    Data Rate - 279.34 kbits/s
    (The video looks terribly compressed. I didn't bother to even test the "Least" setting)

    Data Size - 930.87 K
    Data Rate - 281.59 kbits/s
    (Though it's data rate is barely larger than the Low setting, it's quality is significantly improved)

    Data Size - 1.86 MB
    Data Rate - 576.77 kbits/s

    Data Size - 12.49 MB
    Data Rate - 3868.63 kbits/s
    (That's a HUGE leap!!)

    I left all other settings and options the same in all these test except for the Compressor Quality slider. I am very confused first that the High setting was this low (compared to the best setting), and also that the difference in bit rate between Medium and Low was so small yet the video in Low was much much worse. Is there something I'm missing? Is Quicktime doing some sort of analysis I'm not aware of in determining encoding settings that are not available to me yet part of it?-- if so what?

    I've always used high in the past because I assumed it would be good enough (obviously I never checked). But from now on I will only use Best. Sure I don't need "best" when exporting for Vimeo or something but I'd rather use specific perimeters for that anyhow. Using Auto settings I assume High means High or at least close to Best. But it's not where near it. Not only when using QT's presets will I never use anything but Best from here out, I'm wondering if I should choose another encoding program altogether, something I've been wondering about for awhile.

    What do you feel does the best h.264 encoding? (Adobe Flash encoder, Compressor,....)
  2. lostless macrumors 6502

    Oct 22, 2005
    I have to say that handbrake does a very good job. Dont get the 9.3 version but the svn builds which is on the handbrake forums. It uses x.264 encoder which is a well known h.264 encoder. It will encode from pretty much any format you feed it, including dvds.
  3. fpnc macrumors 68000

    Oct 30, 2002
    San Diego, CA
    When you select "Quality" you aren't really targeting a bitrate, you're telling QuickTime to compress the video in a method that tries to maintain a constant degree of quality throughout the video, more-or-less regardless of the bitrate. However, if you are using the single-pass setting then that can be somewhat difficult for QuickTime to achieve (i.e. your mileage may vary). That's basically why the two-pass option is available, so that you can achieve a more consistent quality throughout the video when you are using the "Quality" slider.

    In any case, if you are concerned about bitrate or if you want to target a specific bitrate then you should select Data Rate > Restrict to.

    The large jump in the "Best" setting is a little surprising, but that could be a near lossless rate that would be far more than needed for something to be simply visibly lossless.

    By the way, I almost never use the "Quality" slider, I prefer to target a specific bitrate that is a good match for the playback device.
  4. rawdawg thread starter macrumors 6502

    Jan 7, 2009
    That makes sense... And for the record all these tests were done with multiple passes selected.

    But if, as you say, QT targets whatever quality setting you've selected independently of bit rate it seems silly that QT would therefore go out of it's way to give you a crappier video quality at nearly the same bit rate simply because you selected Lower instead of medium. What I mean is, it makes sense it's not targeting a bit rate since as you pointed out, if I wanted a targeted bit rate I have the option of entering it, but instead it's targeting the quality. But it's funny it appears QT goes out of it's way to make the video very poor at almost the same file size simply because I choose Lower instead of Medium. Their size is almost identical. Funny it's even an option and I wonder what it does to deliberately make it crappy.
  5. huntercr macrumors 65816

    Jun 6, 2006

    It's the algorithm... this is true of JPEG, MPEG2, just about anything...once you get below a minimum quality threshold, you start getting diminishing returns per byte can't get much lower. It also depends on the actual video clip, how much option there is going on in the scene, etc.

    I always recommend that people manually set their bitrates ( and keyframes ). Only you know what you can tolerate and what you are bothered by in terms of artifacts and smoothness and quality.
    If I'm doing a project I take 20-30 second clips from different scenes in my video and export them together as a sort of summary sample video. Then I'll play around with the bit rate and see what I can be comfortable with. This is only necessary when you're trying to do something online really.... now days if you're exporting to Apple TV or whathave you the filesize doesn't matter, so crank up the bitrate.

    So when you're exporting for the web and are targeting that 300kbit-700kbit mushy area you really have to play around. Lowering resolution to 640x480 ( if you're going to watch on a Mac it's going to render it at that resolution anyway for 4:3 ), the frame rate to 20fps, and picking a very high number of frames between keyframes will help squeeze down a ton.

    But like I said, unless you're putting this on the web... crank it up, man. You're still getting 4:1 compression in your "Best" example.

    Good luck!

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