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Audio badly out of sync after transitions

Kenn Kong


I have been editing captured TV programs and burning them to DVDs with good results for well over a month now.


Then I went to burn the season finale of 24 last Tuesday, and I haven't been able to get things to work right since.


The basic problem is that the video before and after a transition is encoded much slower than the audio. I can easily see this while editing episodes of 24 because each scene begins and ends with a digital clock. At the end of a scene, the last three seconds of the clock ticking takes about 6 seconds in the rendered video, and the first three seconds of the next scene takes another 6 seconds, while the audio keeps plugging away at original speed. The result is that after a transition, the video is about 6 (or more) seconds behind the audio.


I even tried sticking a 5 second black panel between the scenes. The video "drag" remained the same. Interestingly, there was no 5 second pause in the audio. It just trucked right along, resulting in an even bigger delay in the video.


If I edit out each scene individually, just trimming the beginning and end, the rendered video has no sync problem. The problem only occurs when there is a transition (I guess I should mention that I don't use any transitions, I am always doing cuts) between scenes.


I am fairly sure this is not an EMC software problem, because the same thing happens with other video editing software I've tried. It seems to have something to do with the transition into and out of "Smart Rendering". The part of the video that is messed up is the part that shows in the preview window while rendering (i.e. not parts where the "MPEG" logo is showing.)


I have reinstalled my video drivers, just in case something got screwed up, but it didn't help.


I just can't figure out what has changed since last week, because before that everything was working fine (well, as fine as EMC 8 gets, which ain't so fine.)


Anybody have any suggestions?


P.S. I did remember one thing I did differently before. I had been capturing I-frames only, and I captured this using the default GOP. I went back and recaptured using IFO, but the results were the same.


Yes, my hard drive is defragged, with about 20 GB free right now. I would try capturing as AVI, but I don't have enough space.


I did a capture in MPEG-4 format, and the video rendered correctly. Note that it uses software rendering to do this (no MPEG logo during the rendering, and _much_ slower.) So, I'm really sure now it's the hardware rendering that's causing the problem, but I can't figure out why it was working before and not now.


FYI, I am capturing in 16:9 widescreen at 720x480 MPEG-2 at a variable bit rate of 8 Mbps max, 7 Mbps target, 0 motion estimation, progressive scan. Note the actual bit rate achieved is about 5Mbps with I-frames only, and 4 Mbps with the default GOP. No frames are ever dropped either way.


P.P.S. I have further confirmed that it is the "smart rendering" that is the problem. I forced it to use software rendering by changing the target resolution to 704x480, and the video renders fine. I tried to force software rendering by using the button in Options, but that had no effect.

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