My S4 won't play a video created by itself.

[rossmcm]

I took a video of around 2 minutes with my S4. The file produced is a MP4 of 152 Mb, resolution 1280x720, 2 minutes duration. The thumbnail displays OK, but when I try to play it with the stock video player, it reports: "play audio data only", which is does - no video.

Same result with VLC.

What gives? - the file is on the external SD card, but I have recorded other videos onto that and they play fine.