Quoting Andrew Quinn <[log in to unmask]>:
> 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.
I assume you mean file sizes.
The audio contributes very little to the file sizes when it's compressed.
> 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?
No. In most likeliness.. the one with the wav audio will be larger... unless you
turn the wav into mono, lower the bit rate and the sample rate (say 8bit and
22khz which is half the standard for CD quality sound).
Overall, the difference might not mean a heck of a lot. I'd typically try to
keep audio with mp3 compression to at least 160kpbs and the relative standard
for "shared networks" audio is 192kbps. The file size saving is tremendous
still, over the wav (or aiff) and typically only "golden ears" will ever notice
any difference... even with 160kbps... but the quality overhead is a good
As I said, the audio portion is very small compared to the video part.
Compare uncompressed video, full size (720x480 or so, depending), where each
frame can be 900K, 30 frames per second... you do the math. :)
The audio, on the other hand, in uncompressed WAVE PCM will be about 10MB per
minute. That same audio in a compressed mp3 format should take about 10% of the
space. The compressed video... will make a bigger overall impact on the final
This has little to do with iMovie at all. It's all about compression in general.
Quicktime and AVI aren't very good with compressing for quality. They are
typically good for maintaining quality while the file is transported or
These days, converting them to mpeg2 for DVD/SVCD or mpeg1 for VCD, or even
better... divX/Xvid is the best compressions for storage and playback I've
used. Seeing an entire 1h30m movie compressed into 700mb with better quality
than my TV on a good say means something special.
Hope in that rambling there was something useful.
) WWRD - What Would Rob Do? )
| Chris Moran a.a.#707 [log in to unmask] |
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