O.k. i am able to play those files and many others without using a codec pack, guess was your choice to decide this. Seems in past with other versions of windows was more of an issue with certain files, seems now i am even able to play more then with Windows 8.1. Personally i do not trust codec packs, just my thoughts.
MP4 is only a container, WMP is unable to play all formats by default without appropriate codecs.
It depends, how was the mp4 file created, but since WMP relies on codecs, there is no other solution.
I myself prefer to use MPC-HC to avoid installing codecs, but some people just like WMP more. :)
MP4 FAQ - Doom9's Forum
The scalpel solution I am thinking of is - and now hold on to your seats - to fix the one missing codecs.
That can also be done by installing it from the K-Lite pack and installing the whole pack obviously helped. But blindly installing a huge number of codeces without knowing, if they had been broken at all, is not what I would recommend. Doing so can cause problems with file types, which before had not even been part of the problem.
K-Lite pack is well refined, it even fixes some errors, unlike others, which just pack up all possible codecs.
They offer 4 versions, Mega one is for people, who actually encode videos, Standard is for the most users.
I once installed that pack in order to make some file type playable, just like carrotmuseum did here as well, and everything seemed to work out nicely.
Some months later however, I got complaints from the user of the according PC that some videos were no longer playing. I investigated and in fact the K-Lite pack had broken the according codec. Before I installed K-Lite, that had been working.
To make WMP support MP4 format, you should install filters for MP4 format and its associated codecs. After you install these filters, all players that use DirectShow technology, include WMP, will support MP4 format. There are a bunch of third party codec packs on the internet that support not only MP4 format, but also many other common formats. Just Google "codec pack", you will find K-Like and CCCP are the most famous of them.
What if you cannot install codec pack? For example, you will play MP4 on other people's computer and you are not authorized to install any program? On this situation, converting your MP4 to WMP natively supported WMV or AVI format with Faasoft MP4 to Windows Media Player Converter is the best choice.
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