Regular Rep: 5 Joined: 20 Nov 2004 Posts: 1,269 | >> MP4S and MP43 both are known Microsoft’s ISO mpeg-4 v1.
A clarification:
MP43 is Microsoft MPEG-4 version 3
MP4S is Microsoft ISO MPEG-4 version 1
They are NOT the same codec.*
>> With ASF-Tools I can convert the ASF into an MP43-AVI withought re-encoding.
That would only work if the source ASF file was MP43. It would NOT work if the source ASF file was MP4S. It would work in the sense that the conversion will occur, but the resulting AVI won’t be readable in any media player, because the MP4S codec is not unlocked for use with the AVI container.
So in answer to your question, if you wish to convert an MP4S ASF file to an AVI container, you won’t be able to do it without recompression into another codec.
* Just some background if you have time to read. From codeccorner.com
“It is widely accepted that Microsoft attempted to take control of the MPG4 standard by coming out with an avi version of the codec prior to the MPG consortium having voted a final standard. The code had to be completely reworked 3 times. [That’s Microsoft MPEG-4 versions 1, 2, and 3, with fourcc’s MPG4, MP42, and MP43 respectively] Making matters worse, MS refused to rename the files, and since they were not backwardly compatible even more distress was created."
Later they locked the version 3 codec so it couldn’t be used with the avi container anymore, but only with Microsoft’s own proprietary asf container. That’s when cracks of the codec (like the infamous Divx 3) were made - they just re-enabled avi encoding in the codec.
(Much) Later, Microsoft released ISO-compliant (or so they claim) versions of the MPEG-4 codec, dubbed Microsoft ISO MPEG-4 version 1 (fourcc MP4S), and Microsoft ISO MPEG-4 version 1.1 (fourcc M4S2). Those codecs only work with the asf/wmv container.
In summary MPG4, MP42, and MP43 (not all versions for MP43) are cross-platform codecs (they work both in avi and asf/wmv containers), and MP4S and M4S2 are restricted to asf/wmv.
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