G.711 audio codec - video plays, but no sound

[Daisyel]

I have some videos that were recorded from ATC-2000 helmet camera and when i am playing those videos in windows media player than i can see the video but there is no sound. I have tried using GSpot and have found that the codecs used are MJPEG and G.711 MULAW. Proposed Codec Solutions and Test is rendering the video fine but it comes up with an error saying "Failed to connect Output pin". I don't know what that means but i want to if there is a fix for this, thanks in advance.

[Bauer's]

Have you installed any third party codec pack? If you have than you an try uninstalling them and play those videos after that. If you still don't get sound while playing those videos than you can refer below article for fixing the issue.
How to Troubleshoot Audio and Video Issues in Windows Media Player