11-05-2008, 09:42 PM

I used a Canon HG-10 to record some video and loaded it using the Large (960x540) setting. After organizing the clips, I tried fooling with the export settings (Frame rate, Key Frames, and the Quality Slider). I tried about 15 variations.

The quality slider made a decent variation in file size, but changing the frame rates and key frames did very little (within 5 MB difference between 8-30 FPS and keyframes from 10 to 150) on a one minute video about 100 MB. I was expecting the frame rate and key frame changes to have a dramatic effect on file size.

I was also using the H.264 codec and a size of 640x360 if that makes any difference.

Any ideas? I can find very little literature on how to really get into understanding these settings. Thank you!

11-06-2008, 03:35 AM

If you preset the rate to say 1000kbits/sec that is 60,000kb for the minute. If you lower the frame rate, you'll notice the image quality will improve. Those bits will be used either way. I look at it like this; the bits you set get distributed over the parameters, such as frame rate, key frames, compression quality, etc.

Set the Data Rate to Automatic and try frame rates 8 and 30. I expect you'll see a large difference in the file size. If the output files end up with data rates that are close, then this suggests the automatic mode hitting some internal limit, as if you had preset the rate.

I don't know if it will help, but you can check out my iMovie Export Guide.

11-06-2008, 08:43 AM

That makes sense. I was leaving the data rate field blank. I'll go in tonight and try auto as well as some different rate limits and see how that affects the size.

11-06-2008, 09:01 AM

I checked out the export guide. Nice job. Is there a way to figure out the data rates of the movies I've made to use as a starting point? I imagine if I want to use 15 frames/s instead of 30, I can just cut the data rate in half and keep the same image quality (but not smoothness). I just need to figure out what data rate looks good at 30, etc.

Thanks again.

11-06-2008, 11:02 AM

Strange. If you left the data rate field blank, then it sounds to me that Automatic Rate would have been the choice and you'd see different size files.

I'm not sure if this is a QuickTime Pro feature or not... When you open a movie in QT, click on the Window menu and you'll see "Show Movie Inspector" (Command-I). The window that appears tells you several things including data rate. The data rate you see there includes the audio track data rate. Anyway, if this turns out to be a pro feature you don't have access to, VLC likely has a similar ability.

In theory your right about cutting the frame rate and data rate in half would give the same quality image. The thing is that there is more to it than that and it usually comes down to experimenting to find what you like. For instance, the larger the Key Frame number, the fewer key frames are available for reconstructive hints of creating the partial frames in between.

This knowledge is helpful because than you can produce the best quality for the limits of your distribution model; web, CD, DVD, size limits, etc.

11-06-2008, 05:07 PM

Thank you very much for your help so far. I used the Quicktime inspector and while the movies have the codec I request and the settings I put for audio, it looks like the visual settings I select are not being taken into account when I movie makes the actual production. The frame rate is 29.97 in all the movies no matter what I put for my desired output. The quality slider did have an effect on the data rate.

Any suggestions on how to have iMovie take all the settings I select into effect? I am installing a software update for the program and hopefully that will solve the issue... Are there maybe some buttons or preferences I am missing to give me more advanced control?

Thanks again!
Jesse

11-06-2008, 05:21 PM

Problem solved! Looks like the update fixed it. I made another movie and the settings I picked went into effect. That little Quicktime inspector is absolutely fabulous. Thanks a lot.

11-07-2008, 09:03 AM

i hope i'm not the only one having this problem... i've been using iMovie to edit, and sharing finished projects back to myvideo camera via its DV/firewire cable. Since i've updated iMovie to sion 6, whenever I try to share something, only the audio gets recorded on the camera.
Is it possible ot run 2 versions of iMovie at the same time?
Does anyone know what the problem may be?

11-07-2008, 11:04 AM

mieliepap, I suggest you create a new post since your issue has nothing to do with this thread.

Clarify which version of iMovie you are using.

The only two versions I know you can run at the same time are iMovie 08 and iMovie HD, the previous version.

I'd look in both preferences, and the export window for an unchecked flag that would exclude video. I don't know if one exists though.