Safariのリファレンス見ると、HTML5で <audio>,<video>タグのサポート状況が載せられています。
該当部分を引用すると次の通り:
音声形式: Safari on iPhone OS (including iPad) currently supports uncompressed WAV and AIF audio, MP3 audio, and AAC-LC or HE-AAC audio. HE-AAC is the preferred format.
動画形式: Safari on iPhone OS (including iPad) currently supports MPEG-4 video (Baseline profile) and QuickTime movies encoded with H.264 video (Baseline profile) and one of the supported audio types.
iPad and iPhone 3G and later support H.264 Baseline profile 3.1. Earlier versions of iPhone support H.264 Baseline profile 3.0.
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