Compression is a many splendored thing. Almost all of the "bit rates"
[a truly key concept] in digital audio/video - along with duration
and resolution (size/quality) and even frame rate - are up for
Also, one wants to do the best compression possible so as to "spend"
the data over time for the best trade-offs. Now to the essence of the
question: how to account for the audio portion.
Using QT and paying attention to which codec is used - and what the
finer settings are, you can save considerably on the overall bitrate.
This is yet another reason to be using QT Pro around here since it is
really easy to determine these things - and it will even do some of
the weird math!!
Usually there are simply two tracks (A+V) to control the compression
style and settings in order to manage the bitrates/quality... In both
cases the most efficient one that will treat the content at hand is
what is desirable - requirements for quality output DO vary.
The best codec(s) are the ones that perform best for the given bit
rate range and playback size according to what is important.
Though it is not good to use uncompressed audio (AIFF/WAV..) for much
of anything, the audio is not nearly as critical as the video.
There are more layers to encoding software than many folks tap into
enough. You are actually using QT pro "transcoding" features when
exporting from the likes of iMovie.
SO - you can actually pick from dozens of options/settings.
My advice is to experiment and then check "movie properties>sound
track/video track" after exporting the same piece w/diff. options
looking and listening and weighing qualitative aspects against the
Streaming (which we DO have dedicated servers for) adds further twists
and inevitably plays with the quality/bitrate equation.
There are many codecs and encoding tools and I use Cleaner quite a bit
because it is multi-format, saves the settings, does batches and so
Through experience I have found some recipes that work well and are in
ever wider use. I'd be glad to coach you on some in-hand examples
case-by-case if you like.
ps) one that works well for developing clear download-and-play style
clips for broadband:
180x240 displayed at 150% using Sorenson Pro 3 at 15 frames per second
with QDesign Music 2 at 22.05khz 16bit - mono
> the College of Ed and Social Services is often involved with iMovie
> projects. My office mate and I began a discussion on saving
> imovies into the QT format and the file sizes such a render
> produces. I found this on-line:
> Movie Size, in pixels
> File Size for 1 minute of video
> 160 x 120
> 790 KB
> 240 x 180
> 1.3 MB
> Web Streaming
> Requires streaming web server, available soon
> 320 x 240
> 4.5 MB
> Full Quality DV
> 720 x 480
> 260 MB
> Expert Settings
> See below
> the question that arose in conversation concerned the contribution
> of audio to the above file size ratios. so several questions come
> to light.
> 1. how does audio files contribute to the above ratios.
> 2. if the audio that a project uses is a wav or from garage band or
> an mp3, how does the different audio files contribute to the above
> ratios. for example, movie a had 5 minutes of video and used an
> mp3 compressed at 128 kps and movie b had 5 minutes of video and
> used a wav file for the audio track, would, when exported, be the
> same size?
> Andrew Quinn, Ph.D.
> Technology for Teaching Lab Coordinator
> College of Education and Social Services
> University of Vermont
> [log in to unmask], 802-656-9605
> AOL AND YAHOO screenname: aquinnuvm
Harley W. Blake III
Digital/Analog AV Tech
University of Vermont