This sample is a MP4 file that uses movie fragments (which is not yet supported by MPlayer). The sequence is 30 secs long, but the MOV demuxer only detects the first MDAT atom so it only playback 15 seconds of video.

Those are the boxes/atoms contained in the au30sec.mp4 file:

f,t,y,p size=16
u,u,i,d size=28
u,u,i,d size=52
u,u,i,d size=36
m,o,o,v size=2258      // General movie description
     m,v,e,x size=80
     m,v,h,d size=100
     t,r,a,k size=1596      // video track description
     t,r,a,k size=450       // Audio track description
m,d,a,t size=742214      // First chunk of data (first 15 seconds)
m,o,o,f size=5492      // Extra segment description
m,d,a,t size=746415   // Extra segment data
m,o,o,f size=188   // Another extra segment description
m,d,a,t size=12051      // and its chunk of data
m,f,r,a size=128      // Movie Fragment Random Access Box (for fast seeking)