audio/video out of sync after decode

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audio/video out of sync after decode

Postby gridsleep » Sat Jan 28, 2006 12:06 pm

I am having a problem with audio not synchronizing with video in Multiquence 2.54. For example, I record video from a television program using my workstation with an ATI All-In-Wonder Radeon card, in DVD mode which produces an .mpg file with MPEG-2 format 720x480 NTSC (525) 61.76MB/m and audio 48KHz 16 bit stereo. On playback, the video plays perfectly. I transfer the file to my laptop which has the Multiquence. The most recent file I worked on is 8,298,455,040 bytes in length. I use ffdshow to decode the file so Multiquence can read the mpeg-2 format (otherwise MQ can only load the audio.) The audio comes in slightly out of sync with the video. By the end of the file, the audio track is over three seconds behind the video track. The funny thing is that, when playing back in MQ, the video shows in the viewer in sync. At that time, the audio track showing below the video track is only *visibly* out of sync. Playback is still in sync. Only after committing the edits and saving the video in .mpg format using bbMpeg, does the audio and video out of sync condition show up. In the instance of this latest file, it took about ten hours to process and save on my 1.5GHz laptop. Can you explain what is causing this problem? Is there some inconsistency or incompatibility with all this software that makes it impossible to produce a watchable video? The problem is not so apparent in short files, but for feature length videos the discrepancy just grows with file length. Should I be using a different decoder? For a while I was running the audio portion through Goldwave to increase volume and save in .wav format, due to the enormous amount of time it takes MQ to scan the audio in an .mpg file (waiting for the audio display to show up in between each edit can be intolerable.) I stopped when I found I can increase volume using the equalizer in MQ. I will try using GW again to see if it produces an audio track that can sync properly, but I won't have that done today and I wanted to post this now. I'll post an update if using GW works better. It is just a puzzling problem with too many variables. Thanks for any assistance.
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SSDD

Postby gridsleep » Sat Jan 28, 2006 12:59 pm

I just saved the audio track of the video as a .wav file of 1,522,856,492 bytes in length. I deleted the .mpg audio track from MQ and loaded the .wav audio. Now, on playback, the audio track is visibly in sync (the progress bar matches the audio scan) but by the end of the track, the video is over seven seconds behind the audio. BTW the video is 2:12:11.712 in length. This is becoming very discouraging. I have not yet saved this to video to see the final result. More later.
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As expected

Postby gridsleep » Sun Jan 29, 2006 1:11 am

The saved .mpg video is about seven seconds behind the audio by the end of the track. I had this problem some months back, but I can't remember if switching from Elecard to ffdshow fixed it or not. This time it is happening with ffdshow. Very puzzling.
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Still no luck

Postby gridsleep » Mon Jan 30, 2006 5:42 pm

I tried upgrading to the latest ffdshow but it does not include mpeg-2 decoding. I had to downgrade to the previous version, although this time I used the SSE-2 version which seems to allow slightly faster transcoding (6.2 fps as opposed to 6.1 fps average, bfd.) Audio and video are still out of sync no matter how I try to manipulate the data. It was working well. Why is it now not working? Very strange.
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Re: audio/video out of sync after decode

Postby GoldWave Inc. » Mon Jan 30, 2006 8:37 pm

The synchronization problem could be related to the frame rate you are using (might be 29.97 instead of 30.0 or vice versa). It could have something to do with the sound hardware. Different brands of sound cards play/record and slightly different rates. If you record a file on one brand of sound card and play it on another, the "real world" times will be slightly different. The only way to correct that problem is to use the Speed effect in Multiquence to adjust the section's playback speed so that the audio is synchronized with the video.

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Postby gridsleep » Mon Feb 06, 2006 5:07 am

Chris, thank you for replying. I tried the Speed adjustment, changing the audio track to 0.99930 (if I remember correctly) to make it seven seconds longer over the two hour length of the video. The pre-playback synchronized almost perfectly. Then, I went through the ten hour save, and ended up with a file in which the audio was twenty seconds ahead of the video by the end. (long sigh). I shall continue my analysis of the problem. It's just so frustrating because it all was working perfectly a few weeks ago.
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Postby GoldWave Inc. » Mon Feb 06, 2006 7:32 pm

Is the synchronization off when you play the entire video from start to finish, or is it off when you start playback near the end?

Some playback programs synchronize the video to the system clock, while audio is synchronized to the sound card's clock. Both clocks rarely match. Sometimes playing the entire file from the beginning will have perfect synchronization initially, but drift over time.

One test you can run is to record 2 hours of audio in GoldWave and compare the elapsed time shown in GoldWave with the system clock just to see how much of a difference there is.

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