Audio/video sync problems converting mts to mp4

I am using Handbrake to try and convert (on my new IMAC) hundreds of .mts files to MP4. I have tried various audio and video settings on Handbrake and after conversion takes place I still end up with the audio and video not being in sync. The video quality is fine. I'd like to stick with Handbrake and am wondering if anyone has discovered the correct settings to get good quality audio and video. I am new to Handbrake and Mac so if anyone out there can offer help please offer it in simple terms. thanks and I look forward to your help.

Can you post the settings you are using and I'll have a look.

Sure, Kevriano

Here are my settings:

On Output, I am choosing format "MP4 file".

For Video, my settings for video codec is "MPEG-4 (FFmpeg)"; framerate is "same as source"; constant quality is moved to "100%".

For Audio, the source is "Unknown (AC3)(2.0 ch)"; the audio codec is "AAC (faac)"; Mixdown is "stereo"; samplerate (khz) is "auto"; bitrate (kbps) is "160". DRC is "0.00".

Some good news: On one file, all I did was change the bitrate from 160 to 128, and the video/audio synced perfectly. So, I think I found the solution. What is perplexing is no matter what I do on another (larger) file I can't get it to sync. Maybe the source for that one had a sync problem. Not sure.

If you have any suggestions, please offer.

Ok the settings seem ok, but a shame you have to use 128 bit rate.
I have found Handbrake to be a little lacking when it comes to audio stream extraction, and I actually do it seperately and mux the audio back into the movie after (MKV encoding here) Handbrake is also no good for adding subs.
Just curious if you have tried audio passthrough instead of downmix?