How to make Samsung Galaxy SL I9003 play AC3?
The solution.

I ended up preferring films in the .MKV format and using mkvmerge for merging audio tracks and subtitles into a video file.

However,

for those who want to watch films with an embedded AC3 audio track, this solution could be useful. It worked on my Samsung Galaxy Tab 4 10.1 SM-T530NU, and I'm sure it would work on any other device.