If You have any problems with playback of downloaded files with Your regular media player, try using one of those for it:
VideoLAN VLC Media Player – Download - It does not require any additional codecs, has it all built in.
Media Player Classic – Download
If You want to use Media Player Classic, make sure You install K-Lite Codec pack too.
K-Lite Codec Pack – Download
- Audio delay (out of sync):
If the file You downloaded has a little audio delay, You can fix it in the MediaPlayer Classic.
When You open the file, right click on the video window, go to "Audio" and click "Options". The window will appear, in the left side, "Audio Switcher" should be active, then u specify audio delay You want to adjust, for example, if the audio is 1s late to the video, You set "Audio Time Shift" as shown below on the image:
"-1000" means the audio will be played 1s faster, the "-" is important here!
If the audio is playing faster than video, You simply do the same, but this time dont put "-" in, just enter value like "1000" which will make the player add a audio delay of 1s.