MP4GetRtpHintNumberOfPackets - Get the number of packets in an RTP hint
hFile Specifies the mp4 file to which the operation applies.
Specifies the hint track to which the operation applies.
Upon success, the number of packets in the current RTP hint. Upon an
MP4GetRtpHintNumberOfPackets returns the number of packets contained in
the current RTP hint as established by a call to MP4ReadRtpHint().