Help in audio-video sync (Dual-Audio from two sources)

[farhanimator]

hello everone!! this is my first post here in doom9 forums... :)

so this is my story. i have a x264 "moviefile.mkv" that contains aac audio but i wanted to make it dual-audio so i extracted audio from a xvid version moviefile.avi and since frame rates and run time will be different so i used audiacity's "tempo change" feature to calculate and match both audio. (and i have done this many times with 100% successful results). but this time a new type of sync error is discovered, audio is sync at beggining and at last but unsync at middle. and it gets more unsync the more i get to middle position. never seen such a sync error. pls help!

here is everything in details:
----------------------------------
Audio1 (aac file with the x264 video)
----- Runtime: 2:22:50
Format : AAC
Format/Info : Advanced Audio Codec
Format version : Version 4
Format profile : LC
Muxing mode : ADTS
Bit rate mode : Variable
Channel(s) : 2 channels
Sampling rate : 24.0 KHz
Stream size : 38.1 MiB (100%)

Audio2 (MP3 file with xvid video)
----- Runtime: 2:16:58 (original un-edited)
Format : MPEG Audio
Format version : Version 1
Format profile : Layer 3
Mode : Joint stereo
Mode extension : MS Stereo
Duration : 2h 16mn
Bit rate mode : Constant
Bit rate : 128 Kbps
Channel(s) : 2 channels
Sampling rate : 48.0 KHz
Stream size : 125 MiB (100%)
Writing library : LAME3.96.1

(however the audio was a little longer than x264 version when really played, so on matching the vocals of both audio files final runtime is "2:16:54" (i trimmed 4 secs using audiacity)
----runtime: 2:16:54 (Edited and matched vocals)
Format : MPEG Audio
Format version : Version 1
Format profile : Layer 3
Duration : 2h 16mn
Bit rate mode : Constant
Bit rate : 128 Kbps
Channel(s) : 2 channels
Sampling rate : 48.0 KHz
Stream size : 125 MiB (100%)
Writing library : LAME3.98r
Encoding settings : -m s -V 4 -q 3 -lowpass 17 -b 128


then i expanded this audio to match audio1 runtime (and x264 movie ofcourse) i.e "2:22:50" using audiacity's tempo change feature
---- runtime: 2:22:50
Format : MPEG Audio
Format version : Version 1
Format profile : Layer 3
Mode : Joint stereo
Mode extension : MS Stereo
Duration : 2h 22mn
Bit rate mode : Constant
Bit rate : 128 Kbps
Channel(s) : 2 channels
Sampling rate : 48.0 KHz
Stream size : 131 MiB (100%)
Writing library : LAME3.98r
Encoding settings : -m j -V 4 -q 3 -lowpass 17 -b 128

[tebasuna51]

Then you have a different movie version (maybe a new scene, maybe incorrect commercial cut points if TV capture).
Make a standard duration conversion (25 fps -> 23.976) 2:16:54 -> 2:22:45
and test if play in sync until a point.