AC3 -> MP3 synch troubles

[MasterYoda510]

I am using Gordian Knot (which uses BeSweet) to encode an MP3 out of an AC3 format audio file and then mux it with an Xvid video.

My trouble is that when I encode the audio as an MP3, it will become significantly out of synch. However, if I encode the audio simply as AC3, it is fine synch-wise. Obviously, this leads to ginormous files and is undesirable.

Is there any certain setting or something-or-other that I need to select or deselect in order to encode the audio to synched MP3?

[tebasuna51]

Is there any certain setting or something-or-other that I need to select or deselect in order to encode the audio to synched MP3?
Try with mp3 Constant BitRate (CBR).

[MasterYoda510]

I tried that to no avail.

One thing I noticed that may help diagnose my problem is that my video file is 1:14:52 in length and my audio file is 1:33:36.

Maybe it's stretching my audio during the encode to MP3?

[tebasuna51]

"video file is 1:14:52 in length and my audio file is 1:33:36."

1:33:36 the ac3, the mp3 or both?

If ac3 is 1:14:52 and mp3 1:33:36 you need uncheck any stretching option in your audio converter.

[setarip_old]

Hi!

Based on the lengths of the video and audio, I presume they're from a movie ripped from a DVD.

1) What is the Title and Region of the DVD?

2) What methodology (software and procedures) did you use to rip both the video and audio from your DVD?

3) What is the indicated length (time) of the ripped .AC3 audiostream (before converting to .MP3)?

[miztadux]

You're problem is hard to guess with little info, more details about the transcoding steps would help...

My bet would be the problem when muxing vbr mp3 into avi.
You could end up with this problem if you say "yes" to the following question when muxing in virtualdub:

"Virualdub has detected an improper VBR audio encoding in the source AVI file and will rewrite the audio header with standard CBR values during processing for better compatibility. This may introduce up to XXXXX ms of skew from the video stream. If this is unacceptable, decompress the *entire* audio stram to an uncompressed WAV file and recompress with a constant bitrate encoder."

The solution woulds be to click "no" or use a more up-to-date avi muxer that implements the vbr mp3 hack, like VirtualDubMod, AviMux or even NanDub:

http://forum.doom9.org/showthread.php?t=117725

[MasterYoda510]

Hi!

Based on the lengths of the video and audio, I presume they're from a movie ripped from a DVD.

1) What is the Title and Region of the DVD?

2) What methodology (software and procedures) did you use to rip both the video and audio from your DVD?

3) What is the indicated length (time) of the ripped .AC3 audiostream (before converting to .MP3)?

The DVD is side A of the limited edition of The Fellowship of the Ring (the one with the theatrical and extended versions). It is region 1.

I used robot4rip to rip and GordianKnot/VirtualDub to encode the video to Xvid.

The AC3 audio length is 1:33:36, same as the MP3. That is the length that the movie should be, but the video is only 1:14:52. When I muxed the video with the AC3, it slowed the video down to 19 fps, synching everything, but when I muxed it with the MP3, it did not. Also, why would I need to drop the framerate to 19 fps? I did IVTC; could that have screwed somthing up?

EDIT: I used NanDub to mux.

[setarip_old]

It sounds like you may have selected the "theatrical version" of the video and the "extended version" of the audio...

[MasterYoda510]

It sounds like you may have selected the "theatrical version" of the video and the "extended version" of the audio...

But if that's the case, why would everything synch up perfectly if I mux the video with the AC3?

[setarip_old]

When I muxed the video with the AC3, it slowed the video down to 19 fps, synching everything, but when I muxed it with the MP3, it did notObviously, the software you are using handles .AC3 audiostreams differently than .MP3 - but who cares?

If, in fact, you've used the wrong audiostream, just re-rip the right audiostream and go from there...

[MasterYoda510]

It would appear that I ripped the correct audio stream because in robot4rip when it asks me to select a PGC, the lengths are 1:33:30 and 1:45:35. So something screwey is going on with my video. I am currently re-encoding it without using IVTC to see if that will make a difference

[setarip_old]

So something screwey is going on with my video. I am currently re-encoding it without using IVTC to see if that will make a differenceDid you first check the length of the ripped videostream, BEFORE converting it to XviD?

[MasterYoda510]

A-HA! I may have found the problem.

I checked the length of the video in Gordian Knot. It was the screwey 1:14:52 nonsense. Now, in the guide I was using, it tells you to change "Field_Operations" from 0 to 1 in the .d2v file. Just for kicks I changed it back. Now it's the correct length!

I'm encoding it now and will mux with the audio and report back when complete!

Thanks everyone for the help. (Here's to hoping I don't need any more!)

[setarip_old]

It looks like the difference is the result of the following "IVTC"/conversion - 1:33.36 x (23.976/29.970)...

[MasterYoda510]

Well, it worked! I'm thinking that step should be removed from the tutorial, as it really screwed me up.

Thanks for the help setarip_old!

[setarip_old]

Thanks for the help setarip_old!You're quite welcome ;>}