I guess if you're putting unrelated audio with video, this doesn't matter much, but the times that I've tried mixing from different sources, I've had issues with sync. The most recent time I tried this was several months ago, when that PBS mux appeared on AMC1 C-band, I noticed that on a couple programs, that they had some weird audio whereby you couldn't get all the dialog by listening to any of the multiple audio streams (I haven't noticed this recently, so hopefully they have abandoned that practice). Anyway, I was thinking that I could create a manual PID entry channel by using the audio from the SD channel on the same transponder, and mix that with the HD video. The sync was WAY off. At the time, I assumed that this was due to the difference in processing time for the HD signal vs the SD signal, ie perhaps the receivers use a bigger buffer and thus longer delay for HD. But on thinking more, I don't think that makes sense. I'm now wondering if perhaps I used the wrong PID for the PCR PID, and I'm wondering here what people who have done this sucessfully have done for the PCR PID?
I think that I used the PCR found in the HD video when I tried the above, however I'm wondering if perhaps it might have worked if I had used the PCR from the SD channel, or wouldn't it make any difference. Basically, I really don't understand what PCR is, and how it's used. Looking at a PCR PID with a binary editor, I think it seems to just be a counter, but I'm not sure if it's absolute time, or if it's just a non absolute counter that is just meaningful between the specific video and audio it's trying to sync? Ie can you really hope to sync up audio from 2 different sources using either PCR?
My suspicion, is that the PCRs are not absolute, but are counters that actually have relatively small maximum numbers before they recycle. The reason I think that, is that I once streamed video from one computer receiver to another computer, and used VLC to record that stream. I was recording a football game, and everything worked OK, until I decided to pause the recording at halftime to save space. What happened, was when I started recording again, the recording was hopelessly scrambled when I played it back. Everything was there, however it would replay the same half play 6 or 7 times, with the starting point progressing slightly each time until it caught up to where the starting point was after the original ending point, then it would go OK for a while, then start this over and over and over again thing on another play. It almost made you dizzy trying to watch it. I was really confused relative to what caused this, but it occurred to me that perhaps this was caused by the PCRs being confused by my having paused for 10 or 15 minutes.
Anyway, my main reason for this post is to see if anyone here can explain how PCR functions with respect to syncing audio and video, and how would this affect things like joining together audio and video that weren't meant to be together, and also how pausing a recording might affect the function of PCR?
:up
