Recording both Audio and Video compressed (speeds up)

We had a 3-day conference and recorded all the meetings. However, when I open the video or the audio the first minute is at normal speed but then suddenly the speed increases, and this 4-5 hour meeting only takes 1.5 hours. This happens on all the 3 separate recordings.

The audio is horrible with all kinds of noise over the voice (there is no problem with the microphone, the first-minute audio is fine). Even when I use software to slow down the speed, the noise makes it almost inaudible. Is anyone familiar with this problem and is there a way to still fix it? 

Thanks a lot!