No audio when moving mp4 to non-Apple device

Some project-mates have recorded a video on an iPhone. All is as it should be when playing the video on the phone and on their macbooks, but when we move the video to our work computers (running Ubuntu), we get no sound.

What do we need to do differently?

A probe reveals this information about 2 audio streams and the video stream:

    Stream #0:0(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 2 kb/s (default)     Metadata:       creation_time   : 2018-12-03T21:15:48.000000Z       handler_name    : Core Media Data Handler     Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 106 kb/s (default)     Metadata:       creation_time   : 2018-12-03T21:15:48.000000Z       handler_name    : Core Media Data Handler     Stream #0:2(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, smpte170m/smpte170m/bt709), 268x480 [SAR 1:1 DAR 67:120], 2107 kb/s, 29.99 fps, 60 tbr, 600 tbn, 50 tbc (default)     Metadata:       creation_time   : 2018-12-03T21:15:48.000000Z       handler_name    : Core Media Data Handler       encoder         : H.264