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Saturday, November 12, 2005

Brian Gary explains video iPod encoding

Brian Gary writes a very detailed post to the Yahoo! Videoblogging group about how to encode your videos for a video iPod:
I've done some fairly extensive tests on getting video to play on the new 5G iPods and here is as summary:

1. MPEG 4 and h.264 are the only codecs that will play. Technically these are both MPEG 4 codecs, meaning that h.264 is MPEG 4 part 10, but there is a difference in size, quality and processor demands between the two.

2. MPEG 4 specs: MPEG 4 is much more forgiving in terms of compatibility and encoding
times but is not as economical in file size and the quality lacks in comparison to h.264.

Max Data Rate: 2048 Kbps

Max Frame Size: 480 x 360 (Note the iPod will scale down to 320 x 240 for playback on
the screen, but will scale up on output to a TV via the cable adapter.

Max Frame Rate: 30


3. h.264: The new iPod is very picky about this one and iTunes acts as a gatekeeper. You may have a movie that plays fine in iTunes and when you try to transfer it to the iPod you get a message that says the file is not compatible with the player. It is worth the hassel, though (even considering the steep encoding times) because the files are small and the quality is great.

Max Data Rate: 768 kbps. Now, the tricky thing about this is that this number refers to the combined data rate of audio and video, therefore if you decide to encode your audio at a 128 bit rate, then you have to drop the video down to 640 kbps (640 + 128 = 768). You can play around with these numbers, but it's best stay in multiples of 16 (that's not aribitrary by the way, 16 bit is a common recording factor, it's just a grouping of 1's and 0's in 16 channels), so 96, 112, 128 etc., then adjust your video accordingly.

Max Frame Size: 320 x 240. This is a 4:3 ratio. Lots of users are shooting DV, that is a 3:2 aspect ratio so what's going to happen when you encode DV movies is that it will be letterboxed on the iPod because the movie will encode to 320 x 213. The letterboxing is slight so you probably won't really notice it. Now if you shot anamorphic (16:9) then the leterboxing will be more aggressive--320 x 180 and that gets a little rough to watch.

Max Frame Rate: 30

Miscellaneous: You must restrict the Profile to "Baseline." That can only be accomplished using QuickTime Pro or Export via QuickTime (or QuickTime Conversion in Final Cut Pro).
Compressor can NOT change this setting, therefore Compressor can NOT be used to
encdode video for the new iPods using h.264. Compressor can ONLY encode compatible
MPEG 4 movies.


4. Audio: AAC (Advanced Audio Coding); 16 bit; 44.1 sample rate; max bit rate 128,
stereo.


5. The easiest way to encode is by using QT Pro 7.0.3 or higher and selecting the iPod (320x140) setting. There are no options to change.

6. You can encode yourself using QT Pro or out of FCP or iMovie using the formulas above.

7. You can use the shareware like Podner (www.splasm.com).


I created a video podcast called, Video Podcasting 101, that takes you through the easiest steps on a Mac. That can be viewed here:

http://www.rippletraining.com/ripplecasts.htm

1 comment:

  1. Steve Watkins replies:

    Hope you dont mind if I debate 2 points you made.

    Maximim mpeg4 res for ipod is stated by Apple to be 480x480, and it
    seems the limit is actually in terms of pixels, you are allowed 230400
    pixels. So resolutions like the following should be supported:

    res aspect ratio
    720 x 304 - 2.35:1
    624 x 336 - 1.85:1
    624 x 352 - 16:9
    512 x 384 - 4:3

    (I havent actually had time to try these resolutions myself yet though)

    The second point is aspect ratios, regarding the way quicktime resizes
    DV footage. We had a discussion on this a few weeks ago, and I was all
    wrong and confused for a while. The mistake I (and it seems Apple)
    made is to forget that DV doesnt use square pixels. So even though the
    horizontal res of DV is 720, thats for rectangular pixels, and the
    actual res when displayed using square pixels should be somethign
    higher like 768. Anyway this makes Apples resizing maths wrong with
    the export to ipod option, and the footage ends up at the wrong aspect
    ratio. DV isnt 3:2. But then Im not so good at explaining this because
    Im in a PAL part of the world where our DV res is a bit different to
    yours, higher vertical resolution (but lower framerate).

    Anyway this page probably makes more sense than me, again it is
    dealing with PAL rather than NTSC but the square vs rectangular pixels
    issue is the same, just slightly different numbers:

    http://tinyurl.com/7m9ul

    So based on that sort of theory, we were assuming that Apple made a
    mistake, NTSC DV footage shouldnt be resized to 320x213, but 320x240.
    And therefore best to avoid the 'export to ipod' option in qt703, and
    do it the more long-winded way so you can control the resolution
    yourself. Though to be honest I think a lot of people are still
    avoiding h264 for other compatibility (& encoding time) reasons so
    they arent using that option anyway.

    Cheers

    Steve of Elbows

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