Hi everyone!
Avidemux doesn't play audio in some MP4 videos. It shows a message "Trouble initializing audio device", and video is playing without sound.
Here is the sample: https://yadi.sk/i/vlu7WQQM33jUnw
Tested: Avidemux 2.6.15 (appimage version from here http://www.fosshub.com/Avidemux.html/avidemux_2.6.15.appImage), Lubuntu 16.04.1 LTS x64.
This should play (MP2 stereo track), it does here.
What are your audio options in Avidemux: Edit: Preferences: under [Audio]?
Select another AudioDevice like PulseAudio or one of the Alsa. You don't have other program running that claims audio device exclusively? Some programs do like mixxx.
Sorry for disturbing, I've found there was no Pulseaudio in Lubuntu. I've installed it and the sound has appeared.