*.ISMV are fragmented MPEG-4 files with
- VC-1 or H.264 for video
- WMA 10 Pro or AAC-LC for audio
The ISMV file format is covered by the ISO MPEG-4 standard, but WMA Pro is not.
MPEG-4 and AAC-LC would be part of the MPEG-4 standard. VC-1 is an SMPTE standard.
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Originally Posted by Ben Waggoner (Silverlight Video Strategist)
ASF was a great format for bit-pumping - the MIPS-per-Mbps ratio was much better than other formats of its era. However, it simply wasn't well set up to allow a byterange to encapsulate a fragment that could potentially be a single closed GOP. Since server hardware is so much more powerful these days, plus proxy caching so dramaticallly reduces the load on the origin server, going for a somewhat more complex server-side parsing methodology made good sense.
The MPEG-4 fragmented format was able to do everything we needed, so it was simplest to just use that rather than make up something new. Plus it's a good excuse to say "moof" in public.
It's our intent to make the Smooth Streaming file format 100% ISO MPEG-4 compatible.
Since we're using standard file formats we expect many other tools will come out that support authoring the *.ismv files at least.
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