What is the purpose of multiplexing and demultiplexing?

[nocam1334]

Just curious what they are used for. I use TMPGEnc to encode, cut, and join mpegs. I noticed them under mpeg tools, but I have never used them. I'm a newbie, just trying to learn about some of TMPGEnc's features.

[Shabubu]

De-mulitplex takes the audio and video bits of a file and seperates them to two seperate files. Multiplex takes a video file and an audio file and makes them into a single file. A MPEG file with audio and video is called a program stream, audio and video seperately are called elementary strems.

Sometimes when encoding TMPGEnc does a bad job of the multiplexing part, so de-multiplexing (making two seperate files) then multiplexing (putting them back together) can fix the error.

[Truman]

http://www.vcdhelp.com/faq.htm

[nocam1334]

Thanks for the input, Shabubu. I have a video where the audio and video are badly out of sync (video is about 5 seconds in front of the audio). I downloaded it off the internet and don't know how it was encoded. Would demultiplexing then multiplexing fix this problem?

[Truman]

If the audio is from start to end 5 seconds behind the video and you are talking about a MPEG video, have a look at this topic.

[nocam1334]

Thanks, Truman. That helps.