Here is my list of bitrates that I commonly use:
Audio Music: 192 kbps AAC. I think it gives a better bass response than the default 128 kbps. I used to use 128 kbps back when I had my first iPod and its “tiny” 30Gb drive would struggle to hold everything. Now with 80Gb at my disposal and a few judicious exclusions, it’s not a problem and sounds better on a stereo.
Audiobooks: If they are in a compressed format (Audible, MP3), I leave them alone. If they come from CD, I rip them using AAC at half the bitrate currently being used for music (currently 96 kbps stereo, or 48 kbps mono), with Optimize for voice turned on. You can get away with a much lower bitrate for spoken-word content because there’s so much dead air, whereas music provides constant sound.
Video: This is a lot more complex. You can grit your teeth and let iTunes convert any video that you can copy into it into iPod format because it’s easy and works every time, but since iTunes 7, for some reason, iPod files seem to be a lot bigger than I remember.
When video launched on the iTunes Store, it was in QVGA (320 x 240 pixels) resolution, encoded with H.264 (700 kbps) and AAC (128 kbps). Because I was trying to get as much video onto my first 5th-gen iPod as possible, I slaved away at making everything match these specs. When iTunes 7 was released, Apple changed to 640 x 480 (or 640 x approx. 350 if widescreen) and increased the bitrate substantially. AIR’s Alpha Beta Gaga music video, for example, weighs in at 1607 kbps (video and audio added together) and 640 x 346 resolution.
That gives the ballpark. I was stunned to find out that the iPod could play these files. I thought the limitations were much lower. A note on the Apple TV: it’s a 720 HD device, which means it can display content up to 1280 x 720 pixels. It’s specs are much better than an iPod, as you would expect. If you want to play content on both devices, obviously stick to iPod-compatible specs.
I don’t use H.264, even though I adore the format. It’s simply because it’s easier to produce iPod-compatible MPEG4 files, which take less processing power to play back. The files are larger, but I simply don’t leave them on the iPod anymore.
That’s what I thought was going to be a brief summary of the bitrates I’m currently using and why. More on how to create files later.