Solution for Audio out of sync on PowerVCR II captures

[infotech]

Hello all,

I have done extensive analysis of the audio and video streams, frames, and bytes captured by Cyberlink PowerVCR. The bottom line is that the audio and video frame rates do not match, so when the capture is edited with a frame editor the two streams become out of sync. In particular the audio is correct but the video is not exactly 29.97 ( I'm obviously talkng NTSC here ). Since it takes a lot of computer time to reencode the video to exactly 29.97 I decided to take the approach of adjusting the audio stream. I wrote a program that drops or adds audio frames to adjust the length of audio stream. I have done hundreds of mpeg clips with this but recently a new program came to light that will do this more elegantly ( though it takes longer). The BeSweet.exe audio transcoder will now stretch or shrink an audio file on arbitrary framerates. BeSweet.exe (and the associated .dll files ) are available at http://www.doom9.org (download section). Be sure you use the 1.5 or greater version which has the soundtouch support.

Here is the step by step process:

1. Demux the original file (must be non-edited) into video and audio.

2. Run BeSweet on the audio. I use the following command line :

C:\Utils\BeSweetv1.5b29\BeSweet.exe -core( -input "file.mpa" -output "file.mp2" ) -2lame( -m s -b 224 -e ) -soundtouch( -r 29999 29970 )

Where file.mpa is the file from 1. above and file.mp2 is the resulting stretched file. The two numbers 29999 and 29970 determine the stretch (the 29999 parameter is the one to adjust). Note that the same command can convert from 44.1KHz sample rate to 48KHz for DVD by including the string "-ssrc( --rate 48000 )" in the line. This is run from the command line ( or a .bat file) and you will need to use the path of where you saved the BeSweet.exe program and dll's instead of my c:\Utils... path above.

3. Mux the video stream produced in 1 and the new audio file from 2 back together. You can check the sync at this point by playing the new file at the beginning and at the end. You can then repeat steps 2 and 3 as necessary with a different value until you are satisfied.

4. Edit

notes:
1) I have noticed that different machines produce a slightly different video rate ( seems to be speed dependent) but any given machine appears to be constant. Once you get the right parameter for the soundtouch value you are good to go.

2) You can capture audio in PowerVCR at 48Khz ( for DVD authoring ) if you leave the "Encoding Format" blank in the Video section of the Profile Settings ( assuming you create your own profiles).

3) A file that has already been edited can't easily be corrected because each edit section has a different error, and a frame editor does not preserve the original time stamps.

4) Single cuts of a few minutes from within a previously unedited clip ( the time stamps are still present) will not show much mis-sync because the editor will sync the frames at the start of the cut. It is when you have long clips or try to cut lots of pieces out of a clip creating a new longer clip where the audo sync problem shows up.

Have fun.

-infotech

[lordsmurf]

I admire this kind of effort, but the problem is still not addressed 100%.

The issue with PowerVCR is that it will drop video frames without dropping the audio. This is not correctable (aside from nasty audio or video cut methods).

The other problem is that the audio is not "true" 48hz recording, but is some sort of quasi-crap corrupt mess.

Even a PTS-based "correction" system like PVAStrumento isn't perfect.

The true solution to MPEG capture, unfortunately, is still to buy a card that is specifically intended for it (ATI AIW, Hauppauge, etc).

This all said, I will bookmark this an make reference to it on the PowerVCR MPEG capture guide I have.

[Evander]

I appreciate the effort too. I wasn't entirely pleased with PVAinstrumento since it cuts too much to maintain sync, so your method may be useful. But I don't use PVCRII so much anymore, nowadays I'm using ULEAD Videostudio 6 for Mpeg capture and virtualvcr for avi capture