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  1. #1
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    Compression / file size help

    Got a cool little Contour HD camera for my birthday recently. Ran it the other day on the HD setting (full quality). A 15 minute file is around 615Mb, give or take.

    So, I bring the file into iMovie, trim it down to 4:37. All I did was add three 3 second transitions and replace the stereo sound from the camera with a song. The camera records with H.264 for the video and AAC for the audio.

    So, why is it, when I export from iMovie that I'm ending up with 1.75Gb plus files? I'm using the same Codecs and didn't change anything else. It seems as though I've decreased the length of the file by roughly 66%. I would like to save a reasonably high quality movie (full resolution & full 30 fps) at the same compression settings the camera uses when it records. Surely this is a simple thing to do. Can anyone give me some hints?

    Thanks!

  2. #2
    No, that's not phonetic
    Reputation: tscheezy's Avatar
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    iMovie has a lot of different ways to save the file. It is possible that if you just chose all the defaults that it tried to "upsample" the movie to a higher quality than the original was recorded at and thus the file grew even if the clip was shorter. Within H.264 there are a few quality settings and if the camera recorded at 'medium' and you exported at 'best' the file could balloon.

    Can you tell us what steps you took to export the movie?

    I just took a Contour HD 720p 5 second clip and exported it in H.264. The original was 1.8 megabytes. At the 'best' quality export it turned into a 12 megabyte file (!), and at a 'medium' export it was 868 kilobytes. The settings play a huge role in file size.

    You may just want to export the movie a few times at different quality settings and name the files accordingly (e.g. Movie_Best.mov, Movie_Good.mov, Movie_Medium.mov, etc) and watch each one and pick the best balance between quality and file size. You should only have to do the experiment once and from then on you will know what settings maximize quality without trying to introduce quality that was not there in the original clip.
    Last edited by tscheezy; 03-08-2010 at 09:56 AM.

  3. #3
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    Quote Originally Posted by tscheezy
    Can you tell us what steps you took to export the movie?
    Sure thing:

    Chose "File" then "Export".

    Chose "Quicktime" then "Expert Settings"

    Hit "Share" and then went to "Options" Video options were as follows:

    Compression Type = H.264

    Frame Rate = "Current" (or 30 FPS)

    Data Rate = Automatic

    Compressor Quality = High"

    Encoding = Best Quality (Multi Pass).

    So, looks to me like the two questions lie within "Data Rate" and "Compressor Quality". Does anyone know what the default data rate and compression quality for the Contour HD might be? It doesn't seem like there's any point in exporting "upsampled" movies, I only need to match the quality coming off of the camera.

    Thanks!

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