Apple's HTTP stream spec

Apple has submitted a specification to the Internet Engineering Task Force, hoping to have HTTP Live Streaming adopted as a universal protocol, reports say. The format already exists in Safari 4 and iPhone 3.0, and should eventually be integrated into Mac OS X Snow Leopard, but does not currently have backing outside of Apple. Should the technology become standard it could potentially replace various audio/video plug-ins, such as Flash and Silverlight.

The specification calls for an MPEG-2 transport stream, as well as version of the M3U playlist format called M3U8. The transport stream is broken into smaller pieces, which are saved separately and later reassembled using M3U8. In the case of real-time broadcasts, the playlist is occasionally refreshed, permitting new segments to be downloaded as needed.

Backup or lower-quality streams are supported through separate playlists, which can be switched between at will. When leaving Wi-Fi range and connecting to a 3G network, for instance, smaller stream segments can be used, accounting for the diminished bandwidth. Broadcasters can further choose to reference encryption files in a playlist, or deliberately block caching.

Although only an MPEG-2 stream is required, Apple is currently using H.264 video compression with AAC audio. MP3 and direct MPEG-2 audio are supported as well. Apple's standard is at the moment available to examine in draft form.

by MacNN Staff