Streaming Media - June/July 2008 - (Page 52) Cracking the H.264 CODEC By Jan Ozer H .264 is undoubtedly the hottest codec around, but there are inherent market forces that complicate producing files that meet the needs of your target playback device or player. These include the fact that there are multiple H.264 codecs available, each with different configurable parameters, and that each H.264 encoding tool reveals a custom set of compression options. So, here’s my attempt to cut through the smoke: an oracle in three parts. First, I’ll tell you what you need to know about H.264 itself, then I’ll describe the H.264 playback environment and, finally, the encoders. The H.264 Standard Briefly, H.264 is a video compression standard known as MPEG-4 Part 10, or MPEG-4 AVC (for advanced video coding). It’s a joint standard promulgated by the ITU-T Video Coding Experts Group (VCEG) and the ISO/IEC Moving Picture Experts Group (MPEG), and it has the full weight of both organizations behind it, delivering plenty of marketing momentum. H.264’s audio sidekick is AAC (for advanced audio coding), which has replaced MP3 and is technically designated MPEG-4 Part 3. Both H.264 and AAC are technically MPEG-4 codecs— though it’s more accurate to call them by their specific names—and compatible bitstreams should conform to the requirements of Part 14 of the MPEG-4 spec. Since the audio side has few options other than data rate, I’ll focus almost entirely on the video side. According to Part 14, MPEG-4 files containing both audio and video, including those with H.264/AAC, should use the .mp4 extension while audio-only files should use .m4a and video-only files should use .m4v. Different vendors have adopted a range of extensions that are recognized by their proprietary players, such as Apple with .m4p for files using FairPlay Digital Rights Management and .m4r for iPhone ringtones. Mobile phones use the .3gp and .3g2 extensions, though I don’t discuss producing for mobile phones in this article. 52 STREAMING MEDIA June/July 2008
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