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This tutorial discusses the technicalities of the iPod’s video capabilities so that you can make smart choices before you decide to convert all of your videos for iPod viewing. Why does this tutorial matter? With the programs we’ve identified, it’s easy to convert files to an iPod-ready format, but time-consuming. Depending on the settings you choose, many computers will take half a day or longer to convert a two-hour movie into an iPod-ready video file, so if you have to repeat this process multiple times for your entire library, you could be giving up weeks of computing time. Picking the right file formats and resolutions is - unfortunately - an important step in avoiding this sort of problem going forward. Understanding the new iPod’s Video Formats: At the time of this writing, the iPod video is capable of decoding (or playing back) videos encoded in either of two codecs, MPEG-4 or H.264. A codec is computer software that can turn digital video and audio data into a single packaged file. The difference between codecs is like a Microsoft Word document versus a basic text file - they may look the same when viewed on your computer’s screen, but each file may contain different hidden computer instructions that you never see. MPEG-4, a fairly well-established video codec, compacts a historically admirable level of video and audio quality into a given file size. H.264, an emerging standard first released publicly by Apple with its QuickTime 7 software, takes MPEG-4’s quality and file size efficiency to an entirely new level. The catch? H.264 requires considerably more processing power to both encode and decode. This means longer wait times when preparing iPod-ready content, and a smaller maximum bitrate (amount of data per second) that the iPod can reliably decode. This second consequence means that iPod-ready H.264 files must be made up of far fewer pixels as an iPod-ready MPEG-4 file, leading to lower quality when using the iPod’s TV-Out functionality with high-end televisions. However, the company has actually simplified the iPod’s real limitations to make them easier for people to understand. Many users have discovered that while the bitrate limits above appear to be absolute, the resolutions are not. Rather, they observed that the equivalent number of total pixels appeared to be the practical limit for both H.264 and MPEG-4 - 76,800 and 230,400, respectively. Like Apple’s own numbers, these pixel limits are useful and simple ways to make sure your files run properly, but these numbers are not technically correct, either. Rather, the correct limit can be stated as follows: For H.264, you’re allowed 300 square blocks of pixels (called “macroblocks"), 16 pixels on a side. For MPEG-4, you’re allowed 900. The widely-published “total pixel limits” for H.264 and MPEG-4 will indeed work in most cases, but not always, and macroblocks yield the right numbers. For example, an MPEG-4 video of dimensions 725 x 315 has less than 230,400 pixels, but 920 macroblocks. Such a file would be incompatible with the iPod. Picking the Format for You: H.264 or MPEG-4 As we have emphasized in similar discussions on the merits of the AAC and MP3 audio formats, it’s not entirely correct to say that H.264 video offers an absolute “higher quality�? or “smaller file sizes�? relative to MPEG-4 video. Rather, the correct statement is that H.264 has a “higher quality at a given file size�? or “smaller file size at a given level of quality.�? What does all of this technical language ultimately mean for you? Storage space notwithstanding, MPEG-4 is likely to be your format of choice if you would like to display high-quality converted widescreen DVD videos from your iPod onto a high-quality television. You’ll pick a resolution with 480 or 720 pixels and encode, with superior results on a TV screen. For iPod viewing only, H.264 is the wiser choice, so long as you’re willing to spend some extra time to initially process your video files. It offers a smaller file size at 320x240 than does MPEG-4, and since this is the native resolution of the iPod’s screen, there’s no sense in encoding at any higher resolution - the iPod scales down anything larger for on-screen viewing, anyway. It’s also worth noting that you’ll notice that 320x240 video runs slightly smoother on the iPod than higher-resolution video, which the iPod must scale down to fit the screen - you will occasionally notice a modestly lower than expected frame rate with 480- or 720-pixel video. We think that the file size vs. resolution debate will continue to rage for months or years to come - standards for acceptable video quality on a portable device are not yet firm, and it’s unclear how much hard drive space users are willing to give up for their movies and video clips. Experiment a bit to find a balance you’re comfortable with for your own iPod video playback needs, and share your thoughts with others in the comments section below. From: http://www.ilounge.com/index.php/articles/comments/the-complete-guide-to-ipod-video-formats-and-display-resolutions/
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