PMT reference help, issues during ad splicing

[explorerst4x4]

Hi guys. An introduction is in order I suppose. Name is Marc. 16 years in CATV, started as an installer, worked my way up to Headend Sr Tech over the years, mostly at a very small cable company in Ohio. Hoping to get some good information from your site.

Problem: We are transcoding MPEG 2 to MPEG4. We also do local digital ad insertion using a Cisco DCM and SeaChange equipment. The ad insertion occurs before the transcoder, when the streams are MPEG2. When an ad plays the transcoder is regrooming the video whenever the ad starts and ends, which causes a freeze in the video. The transcoder vendor says they are seeing a change in the PMT table when the splice occurs. I put a transport stream analyzer on the video and all the PIDs stay the same, but in the alarm index I see a PMT reference table change alert. As far as the PIDs go, when I first look at the stream with the analyzer, I see everything but the SCTE 30/35 PID, which then shows up after a splice occurs. The transcoding device also acknowledges the splicing PID as being there beforehand. I am not seeing any unreferenced PIDs showing up at any time. I am familiar enough with PIDs and the like, but I don't understand what is changing in the PMT reference table to make this occur, especially since I don't see any PIDs that aren't normally there. Can anyone clue me into what is happening?

[explorerst4x4]

This is all live video, not files.

[chowmein]

Maybe you could try the Videoredo forums, the developers are active there and they know their PIDs from their PMTs.

http://www.videoredo.net/msgBoard/index.php

[explorerst4x4]

I figured out what was happening. The encoded ads had a secondary audio that was encoded as MPEG1 instead of AC3. 99 percent of our audio streams are AC3. The PID didn't actually change, just the descriptor for the audio in the PMT reference table. When the transcoding equipment saw the descriptor change it would regroom the channel when the ads started and then regroom when the local ads stopped. FYI.