This also changes the way frames are written in the WebM muxer. Now,
frames are stored and written on the next call to AddSample. So each
call to AddSample will write the previous frame. This is needed to
determine whether the given frame is the last one in the cluster.
Closes#70
Change-Id: Ic69ebad3c4729cdaa2017c9c7f497048501ac907
Now outputs cenc:default_KID attributes on all ContentProtection
elements for non-MP4 streams. For MP4 streams, it will still output
the default ContentProtection element.
Closes#69
Change-Id: I38b24297aa3c2ccbcbde38b44279b56c37a388f7