Store correct time stamps in recorded mp4 files

According to the specification (ISO_IEC_14496-12_2008 page 17, 19 and
21) the time is "in seconds since midnight, Jan. 1, 1904, in UTC time"
which is not the same as Unix epoch time. This is already correctly
handled in MPEG4Extractor.cpp when reading files.

The specification also supports 64 bit timestamps which would make
it a bit more future proof, but unfortunately it seems like support
for this in players are poor (tested both Windows media player and
Quicktime player).

Change-Id: I102d728f098b8b0a21013956f017b0c4f2d69112