asf patch by (Konstantin Andreyev <kandreyev at bcsii dot com>)
1. Corrected packet sent time. (Packet sent time => previous packet sent
2. Corrected payload playing time. (Payload playing time => packet sent
3. Used different format for packets with one payload and multi payloads.
Originally committed as revision 2851 to svn://svn.ffmpeg.org/ffmpeg/trunk