Video and Audio of out sync

[videohelpuser]

Hello !!

First Thank in Advance for replying. I bet this has been solved before though it was for different purposes.

I usually use a camcorder that gives out 1440 x 1080 video, 16 Mb/s bitrate, 29.970 FPS (NTSC) to record discourses. Audio attached by camcorder has AC3, 448 kb/s, 6 channels, sampling rate of 48 kHz, frame rate of 31.250 (according to mediainfo). I thought audio does NOT have frame rate but MediaInfo shows it.

But audio is not very good in a Hall so I put a lavalier microphone on the hall's microphone. I record it in Audacity and sound quality comes superb.

But when I edit the resulting video file (remove the audio and attach the Audio created in Audacity (mp3 - 360 kb/s)), there is a huge out of sync. It progressively becomes worser.

Can somebody please help in how to change the Audacity recorded audio file to have it in complete sync with Video?

[davexnet]

The M2TS, video and audio, shows a running time of 2 hours 59 minutes, while the mp3 has a running time of 2 hours 22 minutes.
How did that happen ? Something go wrong in your conversion to mp3 ?

[videohelpuser]

Thanks davexnet. Please ignore the times. I edited the audio and video to start at the same time but there was a huge out of sync that came worse as time progressed. I sent the older mediainfo instead.

I use filmora to edit the video file. Remove the audio that came with video. Drag and drop the audacity created audio. Sync it so that it is perfect with the lip movement at the beginning. But as time progresses, it goes out of sync. It is not a CONSTANT lag - it increases as time progresses.