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In VLC 3.0.1 to 3.0.6 (and 3.0.7 nightly for that matter), when using Open Multiple Files dialog to play a video file and an external audio file (using Play another media synchronously checkbox), the program won't work correctly:
1) firstly, it won't play any sound after you switch audio track to Track 2 until you skip to any frame using timeline, and then sound starts playing but video and audio start from the very beginning;
2) secondly, if you'll keep trying to get to specific position using timeline the program would crash on 2-3 time.
This makes VLC unusable because you have to play video with external audio in one go. Please fix this. I've tried this with different files (specifically, MP3, FLAC, MKA audio files with MP4 and MKV video files) and it's broken.

Hi,

This looks very weird, did you try on other computers?

Hi, unidan, thanks for having a look. Nope, I don't have any other computer. However I'm experiencing this with many files of this kind. My computer is MacBook Pro with Retina display (Mid 2012, Inter Core i7, 512 GB SSD, 8 GB RAM, GeForce GT 650M, latest GPU drivers) running Windows 10 Enterprise N LTSB 2016. I've merged MKV and MKA (external audio file) to single MKV file (I'm familiar with mkvmergeGUI) and removed original audio track leaving just the external one. Thus the file seeking works absolutely correctly with no issues. I suspect the issue might be related to codec used for external audio track (original audio track is FLAC, external audio is reported to be FLAC by VLC and AAC by mkvmergeGUI) and VLC just fails to synchronize it correctly. Oh, I forgot to mention: I've tried extending caching ms and setting output module to automatic. I've uploaded both MKV and corresponding MKA for anyone that wight have a look and double-check if I'm correct. And here's mkvmergeGUI-produced MKV with only external audio track and it's working correctly.

Hi. I confirm bug described by topic creator. Checked clean-install version 3.0.6 on Windows 10 and Ubuntu 18.04, my hardware is Dell G5 5587. Tested on several files, all of them played fine by VLC in single-file mode. I can provide files to reproduce bug if required.

I did exactly as how-to recommends. First audio track (included in video file) works fine, but when I change it to second track, sound disappears. Moving to some video position (like +1 min) resets playback to start.

The only workaround I see at the moment is to use convert function to combine these two files, it works fine, but not really solves problem due to long conversion time and lot of manual work. Here some media information.

video mkv
Codec: H264 - MPEG-4 AVC (part 10) (avc1)
Decoded format: Planar 4:2:0 YUV 10-bit LE

audio mka
Codec: MPEG Audio layer 1/2 (mpga)

Thanks for confirmation, ndp. During further investigation I came to conclusion that this bug is somehow connected to main video file format (not audio), because if you'll use audio example (MKA file) from previous post with any different MKV/MP4/etc. it will work correctly. So it seems this issue has to do with video file format in the MKV container.

I have just encountered the same bug, still present in 3.0.8.

Confirming that synchronous play on 3.0.8 does not work with .mp4 video files either, on windows 10

Bug still present in 3.0.11. .MKV files don't want to be played with external sound files. It crashes if you use the timecode, won't even play the new sound either anyway. I mean, the video does keep playing, but if you choose the new sound file there will be no sound. And if you click on the timeline/timecode (whatever it is called) it just crashes.

got the same problem, looks like found some workaround
try to open not a .mkv, but .mka and to .mka attach .mkv
don't know why, but if I try to attach .mka to .mkv, does not work nothing - after switching audio source sound just completly dissappears
but if I try to attach .mkv to .mka, sometimes it does not work at all, player does not start and only scroll-bar animation shows, but sometimes all works fine, like 50 / 50

Still broken on 3.0.12 for MP4's on Win10.

Works fine on 2.2.8
https://get.videolan.org/vlc/2.2.8/

Confirmed, broken in 3.0.12 (Win 10) for .mkv/.mka. Workaround with .mkv attached to .mka not does not prevent the crash from using timeline, works only when video is played in one go.