by Zarxrax » Fri Mar 30, 2007 9:42 am
Resolution is probably the single biggest factor that affects playback speed. HD resolutions simply require much more processing power to play smoothly than standard definition videos do. Also HD videos contain much more data than a standard resolution video, so you want to compress it more efficiently. H.264 is currently the most efficient encoding format, but also one of the hardest to play back. Fortunately, it is very configurable, so various settings can be tweaked to make a compromise between compression efficiency and processing power required.
Apple uses H.264 for their videos, but their encoder does not contain many advanced options so it can't compress as well as an H.264 encoder like x264 can. As a result, it can also play back on system with slower cpus.
The x264 encoder that everyone uses provides much better compression techniques than apples encoder, and so it requires a stronger cpu to play back using these features. However, x264 is a very configurable codec, and can be set to encode in much the same way as Apple's encoder does.
So in the end it's a tradeoff--do you want a smaller, more efficiently compressed video, or do you want a video that will play on slower cpus? According to your needs, you can configure the settings in x264 how you want them.