interesante explicación sobre este decodificador (copiado de la web de ZP):

"H.264, also known as MPEG4 AVC (or Advanced Video Coding) is one of the best video compression standards in existence today.

While still under the MPEG4 specification, it has nothing to do with the MPEG4 used in XVID/DIVX. It is a more advanced format requiring a much stronger CPU to decode. This format is relatively new and encoders/decoders may not support the full standard at this point, or offer true compatibility between encoders (which can create playback problems later on), which is one of the reason the format hasn't taken off more.

It has been chosen by apple for use in their HDTV video clips within the QuickTime v7 environment and may be used in the HD-DVD standard for video compression. (negrita mía)

As the format is somewhat new, playing H.264 clips may be a bit of a hassle. Currently, using a recent versions of ffdshow is the best open-source choice for this format. Additional decoders may be found in the Nero Suite or with the Elecard Decoder Pack (The H.264 decoder may not be included in all of Elecard's or Nero's installation packages). "