h.264 optimize for cd/dvd vs. download?

Discussion in 'Digital Video' started by Joz3d, Apr 25, 2009.

  1. Joz3d macrumors member

    Joined:
    Jul 19, 2008
    #1
    Hey all,

    I'm exporting video from iMovie using "Export using QuickTime" -> "Movie to MPEG-4" and using mp4 (h.264). The only thing I'm not really sure about in this dialog is the "Optimized for:" drop-down. The options are CD/DVD-ROM, Download, and Streaming. I understand that the result is that some optimizations have a higher threshold of bitrate variation than others, but which one should I use for preserving movies just on my hard drive? I'm not sure which to choose between "Download" and "CD/DVD-ROM"? It seems like CD/DVD-ROM would yield the highest quality? But does that instead just keep the bitrate more constant for better playback on DVD players, etc? I'm encoding at ~1.5mbps. Any advice on this would be appreciated.
     
  2. DoFoT9 macrumors P6

    DoFoT9

    Joined:
    Jun 11, 2007
    Location:
    Singapore
    #2
    hhmmm..

    im quite fussy with my movie quality, so i use the "Full quality" setting. a 4minute movie will come out around 1gb.

    those settings (cd/dvd, download) just compress it further (including the resolution). download looks appalling.

    CD/DVD is probably the best if your burning to a cd/dvd, however for file longevity and whatnot i would use "Full quality"
     
  3. Joz3d thread starter macrumors member

    Joined:
    Jul 19, 2008
    #3
    Whaa?? But there's no such option. I'm not burning it anywhere. I'm just going to keep the movies on my hard drive. You have to choose one of the options, and I don't have a "Full Quality" one.
     

    Attached Files:

  4. DoFoT9 macrumors P6

    DoFoT9

    Joined:
    Jun 11, 2007
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    #4
    oh what!!!!! are you running imovie8/9 ?? grrr they should of left that setting there. i guess you will just have to try a few settings yourself and see how you go.

    3000kbps should be ok, but that would still be compressing it somewhat. experiment! haha

    p.s. use the CD/DVD setting
     
  5. Joz3d thread starter macrumors member

    Joined:
    Jul 19, 2008
    #5
    Oh hah, yes iMovie '09. Yeah I'm guessing CD/DVD gotta be the best and they get less of a bitrate window as you go down.

    I do my vids at 1500kbps just because I like the resulting file size/quality ratio. Plus the source on these particular ones I'm doing now isn't anything spectacular, they are just 640x480 photo-camera vids.

    Thanks for your help. :)
     
  6. DoFoT9 macrumors P6

    DoFoT9

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    #6
    aahhh ok then the bitrate wouldnt be anything over what your currently converting to anyway :)

    have fun with it all!!

    no worries :)
     
  7. Joz3d thread starter macrumors member

    Joined:
    Jul 19, 2008
    #7
    Well I'm not quite sure about that. Camera vids are MJPEG. So the bitrate is v.high but I don't know how much that means when there's no motion compensation, but QT says that their bitrates are around 15mbit. *shrugs*
     
  8. DoFoT9 macrumors P6

    DoFoT9

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    Jun 11, 2007
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    #8
    if quicktime is saying 15mbit, then that is around 1.875mbyte, or roughtly 1800kbps. e.g. 1500kbps is about the same :)
     
  9. Joz3d thread starter macrumors member

    Joined:
    Jul 19, 2008
    #9
    I don't think that math is correct. 15 mbit ≠ 1500 kbit. Unless I somehow didn't understand correctly for the past number of years that "mbit" is the same as "mbps" and "kbit" is the same as "kbps" :)

    1.875 mbyte = 1875 kbyte / 15000 kbit / 15 mbit

    0.225 mbyte = 225 kbyte / 1800 kbit / 1.8 mbit
     
  10. DoFoT9 macrumors P6

    DoFoT9

    Joined:
    Jun 11, 2007
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    Singapore
    #10
    haha oh you poor fellow. im afriad "mbit" and "mbps" (or megabytes per second) are different things. its stupid. we will have to show them properly...

    in computing there are bits, and bytes. 8 bits = 1 byte.

    the number you gave was 15megabits. to get this into megabytes (which is what hard drive manufactors work with, thus the deduction in actual space when you buy a 500gb (gigabit) HD and you only have 465.8gB(gigabytes) to use!) you have to divide it by 8.

    so 15mbits = 1.875mbytes.
    1.875mbytes = ~1875kbytes (or 15000kbits)
    1875kytes = ~1.8mbytes, which is close enough to your encoding bitrate of 1500kbyets (1.5mbytes) per second.

    i hope you can understand haha!

    hmm i have made a mistake there too, not in my maths but in the export usage of bits/bytes. ill try figure it out.

    ok. if your exporting at 1500kbits. that is 1.5mbit, the original is 15mbit as you said. hmm so that is a fair decline in quality. my mistake.
     
  11. Ocean Sea macrumors newbie

    Joined:
    Jan 6, 2010
    #11
    Regarding the initial post: I've been trying to figure this out too and I can't find any info on it. So I decided to do some tests.

    Using MediaInfo (GUI_0.7.30) I examined two identical (SD) mp4 H.264 files exported from iMovie 09 using Export using Quick Time.

    (a) was set to Optimized for: Download
    (b) was set to Optimized for: CD/DVD-ROM

    The main difference between the two was file (a) "Format profile" was Main@L3.0

    whereas file (b) Format profile was Main@L5.0.

    Now I don't really understand profile levels but from what I can make out from Wikipedia it seems file (b)'s profile level (L5.0) allows for better quality.

    One other difference MediaInfo highlighted was something called Bits/(Pixel*Frame). I have no idea what that is but for file (a) it was 0.205 and for file (b) it was 0.207. I am guessing this is a result of the profile levels but that's just a guess.

    Hope this helps somewhat. I'd love to hear a proper explanation of the difference between the two options.
     
  12. simplebeep macrumors member

    simplebeep

    Joined:
    Sep 28, 2007
    Location:
    SLC
    #12
    Alright, let's put this matter to rest. According to Apple's Developer Docs:

    In other words, this setting is about how much the data rate is allowed to fluctuate from the average, as optimized for certain media.
    Download = little/no constraint
    Disc = somewhat constrained
    Streaming = very constrained.​

    (Quoted from; see "Recommended H.264 Compressor Settings")
     

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