MPEG-4, h.264 is the way to go now for youtube and other web stuff. Why WMP won't play mpeg-4's is more political than technical.
From Microsoft @
http://support.microsoft.com/kb/316992
MPEG-4 (.mp4)
MPEG-4 is an International Standards Organization (ISO) specification that covers many aspects of multimedia presentation including compression, authoring and delivery. Although video compression and file container definition are two separate and independent entities of the MPEG-4 specification, many people incorrectly believe that the two are interchangeable. You can implement only portions of the MPEG-4 specification and remain compliant with the standard.
The MPEG-4 file format, as defined by the MPEG-4 specification, contains MPEG-4 encoded video and Advanced Audio Coding (AAC)-encoded audio content. It typically uses the .mp4 extension. Windows Media Player does not support the playback of the .mp4 file format. You can play back .mp4 media files in Windows Media Player when you install DirectShow-compatible MPEG-4 decoder packs. DirectShow-compatible MPEG-4 decoder packs include the Ligos LSX-MPEG Player and the EnvivioTV.
For more information about the Ligos LSX-MPEG Player, visit the following Ligos Web site:
http://www.ligos.com (
http://www.ligos.com)
For more information about EnvivioTV , visit the following Envivio Web site:
http://www.envivio.com/products/ (
http://www.envivio.com/products)
Microsoft has chosen to implement the video compression portion of the MPEG-4 standard. Microsoft has currently produced the following MPEG-4-based video codecs:
- Microsoft MPEG-4 v1
- Microsoft MPEG-4 v2
- Microsoft MPEG-4 v3
- ISO MPEG-4 v1
MPEG-4 video content can be encoded and stored in an .asf file container by using Windows Media Tools and Windows Media Encoder. You can then play these files in Windows Media Player. For more information about Microsoft and MPEG-4 support, visit the following Microsoft Web site:
http://www.microsoft.com/windows/windowsmedia/forpros/format/codecdownload.aspx
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My own edit:
Oh, I know, let's not support an ISO standard and instead implement our own proprietary one! Yeah, that won't confuse anyone!