The iTunes Podcasting Team has sent out an e-mail to makers of video podcasts listed in iTunes about how they should encode their video for the best compatibility with the AppleTV. However, these tips are actually useful for anyone who (re-) encodes video for display in iTunes, on the AppleTV, on an iPod, and, soon, on an iPhone.
The Podcasting Team points to the podcast tech spec page, and offers three additional tips:
- Use a resolution of 640×480 (4:3 aspect ratio) or 640×360 (16:9 aspect ratio) for the highest quality video that's still compatible with the iPod.Don't use different feeds for different versions of the same content: this fragments the ratings for the podcast.Don't add black bars to your 16:9 content to make it fit in a 4:3 resolution (i.e., letterbox), this prevents the AppleTV from making the video fill the entire screen; black bars will show on all four sides.
I'd like to stress the third point: this is also really annoying for iPod users, because the iPod can either show widescreen video letterboxed, or it can zoom in and make the middle of the video fill the entire screen. With pre-letterboxed content, the second option is gone and 40 percent of the already tiny screen is filled with black bars. On the large screen, I'm a big fan of widescreen content, and I'll even accept a black bar or two, but content on the iPod is tiny enough as it is.
I like to encode video from various sources, such as DVD, a DV camcorder, or the Elgato eyeTV for later viewing in either iTunes or on the iPod. Unfortunately, simply choosing a target resolution isn't enough to get the job done, or at least, not enough to get it done well. A big problem with many kinds of video, especially if it's older, is overscan. To a computer monitor, 640×480 means 640×480. To a TV, on the other hand, it means that it will definitely show you the middle 560×420 or so pixels, but a row of 40 pixels on the left and right and 30 pixels on the top and bottom may either be visible or fall under the edge of the screen. This is the only way to make sure that the picture fills the entire screen on older TVs.
The trouble is that towards the edges of the overscan areas, there are often black bars or all kinds of artifacts in video that do not add to the viewing experience. So it's often a good idea to crop away some of the overscan area. Around 5 percent on all sides generally does it. This means that if you use iSquint to convert video to an iTunes/iPod/AppleTV-friendly format and the overscan area contains unpleasantness, removing 32 pixels on both sides and 24 on the top and bottom is sure to do the trick. This leaves you with a 576×432 picture. 16 and 12 for a 608×456 result may also work.
It gets more complex when you want to rip DVDs (or DV video) to MPEG4 or H.264. DVDs use a 720 or 704 pixel horizontal resolution, but 480 lines for NTSC and 576 lines for the European PAL TV norm, regardless of whether the content is in 4:3 or 16:9 aspect ratio. Fortunately, you can easily compensate for that by choosing 640×480 for 4:3 content and 640×360 for 16:9 content. That does throw away a good amount of detail, though. If iPod compatibility isn't an issue, these are resolutions that don't lose any information:
TV NormDVD/DV resShould beNTSC 4:3720x480640x480NTSC 16:9720x480854x480PAL 4:3720x576768x576PAL 16:9720x5761024x576
However, the popular Handbrake software doesn't support these resolutions currently. Both Handbrake and iSquint will produce either MPEG4 or H.264 video files in .mp4/.m4v format. If you use Handbrake, or harder to use software such as ffmpegX, you can make different kinds of H.264 files. Unless you really know what you're doing, stick to the baseline or low complexity profile and keep the bitrate to 1.5Mbps for H.264 or 2.5Mbps for MPEG4. See the tech spec page for more detailed information.
Last but not least: in Handbrake, you can choose a file format. This needs to be "MP4 file" for compatibility with iTunes, but if that's not your main goal, you can also select "AVI file" and rip the 5.1 surround audio (AC3) from the DVD, which you can subsequently play over the digital output of your Mac for external decoding with VLC.