This func will return the first and last PTS from an MPEGTS clip by finding the first access unit, and then by moving backward from the end of the clip to find the start of the final PES packet.
Wrote a test to check mts encoding of video to validate packet creation etc. Test is failing because how I did mts
encoding is interesting, thinking about changing.
Completed test TestFindPid to validate function of FindPid func in mpegts.go. Through this
process, it was found that there was a bug in this func, whereby the returned packet was
not complete due to indexing issues. The bug is fixed and the test passes.