Hi! I sent a patch that probably fixes this issue, very short transport streams were never auto-detected by FFmpeg. http://ffmpeg.org/pipermail/ffmpeg-devel/2016-May/193698.html
Possible workarounds are to increase the audio length with "sine=d=0.2" or to set an explicit audio bitrate of 128k with "-b:a 128k" (this was the bitrate in FFmpeg 2.8, when the aac encoder was still experimental) to increase the output file size. Thank you, Carl Eugen
