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PRE-ARTICLE HEAD NOTES
(a) This is a Generalised Tutorial, thus I will try not to refer to specific tools.
(b) If a similar tutorial has been posted previously then I apologise in advance.
PROBLEM:
When transcoding from format X to format Y, audio and video Synchronisation errors occur.
SOLUTION:
(1) The audio stream and video stream first need to be separated, any program and or utility that allows you to do this fine, different tools may be required for different formats. An example tool that can be used (usually intended for AVI, but can accept MPEGs to) is VirtualDUB.
(2) The Audio stream needs to be decompressed from its current compression. When you decompressed you should have a .WAV file.
(3) Now you need to "Fit" decompressed audio stream to the video stream. Generally I have found that there are two cases:
CASE A: EXCESS TRIM
When you decompress you will find that the audio is actually longer than the video stream, if you look at the audio file you should notice that near the end of the audio stream is just blank, or excess. Simply cut down this excess audio stream to exactly match the length of the video. Sometimes the excess can occur at the beginning of the audio stream.
CASE B: UNEVEN
If the above is not the case then you have to manually sync the streams by hand, this can be simply done by using any good NLE (Non Linear Editor). Place the video stream on the timeline and then place the audio stream and "slide" the audio stream until you find good sync.
(4) Save your new edited .WAV audio stream
(5) Open up your encoder and select the edited .WAV file as your audio stream and start encoding. You may even encode/render directly from your NLE in which case you can skip (4)
(6) Delete all unused files. And enjoy your movie!
That is the end of this Simple tutorial
I hope that helps.
Anhar Hussain Miah
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