First, and most significant, is that Apple now recommends using different audio bitrates for the different quality streams, starting at 64Kbps and scaling up to 128Kbps. In all previous versions of the Tech Note, Apple used 64Kbps across the board, which most authorities attributed to the potential for “popping” artifacts if a viewer switched to different rates during a stream switch. Adobe’s adaptive presets took the same approach, and most white papers on the subject advised the same.
The other major change is the adjustment of the recommended segment size from ten seconds to nine seconds, which cleared up the most enduring mystery of the Tech Note. As I wrote in How to Encode Video for HLS Delivery: "In terms of segment duration, the most confusing aspect of TN2224 is the recommendation of a segment size of ten seconds, and a keyframe interval of three seconds, as this wouldn’t seem to produce a keyframe at the start of each segment. Interestingly, the new default settings in Apple Compressor 4.1 follow these recommendations, creating a segment duration of ten seconds, but using a keyframe interval of three seconds.
In contrast, most authorities recommend making sure that the keyframe interval divides evenly into the segment size. For example, cloud encoder Zencoder’s well-written Best Practices for Encoding HLS Video states, “keyframe rate should be an even interval of the segment size.”