Many times we get some videos or Audios via web or from some of our friend but when we try to play that video we got error or you might see only video but wont get audio or vice versa.
This happens due to the missing codecs in your media player. Codecs are the certain set of standards for Audio and Videos which are used to decode your file. But if you had missing codec then you wont be able to play file.
You can install Windows 7 Codec Pack on your system, it supports lots of media formats like mkv, bdmv, evo, avi, flv, mp4, ts, webm, m4v, m4a, ogm, ac3, dts, flac, ape, aac, ogg, ofr, mpc, 3gp and many more. You can also able to view all HD videos too after installing this codec pack.