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De-multiplexing: Does it affect quality?

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Bob Cole
De-multiplexing: Does it affect quality?
on Jun 28, 2005 at 1:18:45 pm

I am re-authoring a show whose source material I originally encoded into a multiplexed file.

I have de-multiplexed using TMPGenc MPEG Tools, so that I can transcode the audio to .ac3.

Does de-multiplexing affect video or audio quality adversely? Should I simply go back to the original material and re-encode into separate audio and video files?

-- Bob C.


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Roadkill
Re: De-multiplexing: Does it affect quality?
on Jun 28, 2005 at 2:37:47 pm

Demultiplexing doesn't affect the quality. It simply splits out the video and audio "as is" from the muxed file.

There could be some issues converting the audio to Dolby Digital (AC3) though. If the audio in the multiplexed file is MPEG-1 Layer II compressed, you will be going from one compressed format to another one. This doesn't always turn out as intended. I would recommend to convert the audio first to uncompressed PCM (WAV / AIFF) audio at 48KHz, 16 bit, stereo and to use that to create the AC3 audio from.


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Bob Cole
Re: De-multiplexing: Does it affect quality?
on Jun 28, 2005 at 6:33:03 pm

[Roadkill] "convert the audio first to uncompressed PCM (WAV / AIFF) audio at 48KHz, 16 bit, stereo"

Luckily, when it did the demultiplexing TMPGenc created a PCM file at 48 kHz, 16 bit, bit rate 1536 kbps.

And the .ac3 file works fine. Thanks!

-- BC


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Dave Friend
Re: De-multiplexing: Does it affect quality?
on Jun 28, 2005 at 7:15:02 pm

Bob,

"when it did the demultiplexing TMPGenc created a PCM file"

That indicates that PCM was the choice when the file was originally encoded. TMPGEnc's MPEG tools does not do anything to the format of any file it demuxes.

Do you have TMPGEnc 3.0 XPress?

Dave



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Bob Cole
Re: De-multiplexing: Does it affect quality?
on Jun 28, 2005 at 11:20:27 pm

[Dave Friend] "Do you have TMPGEnc 3.0 XPress?"


I have TMPGEnc Plus 2.5. Why?


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Dave Friend
Re: De-multiplexing: Does it affect quality?
on Jun 29, 2005 at 3:24:56 pm

[Bob Cole] "I have TMPGEnc Plus 2.5. Why?"

I would explain my workflow to demux and create ac3 files from a mpeg2 program stream with PCM audio.

Does TMPGEnc 2.5 support the ac3 plug-in?

Dave


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Bob Cole
Re: De-multiplexing: Does it affect quality?
on Jun 30, 2005 at 1:44:13 am

[Dave Friend] "Does TMPGEnc 2.5 support the ac3 plug-in?"

Guess not -- I didn't see that mentioned in TMPGenc Plus 2.5 files. I think TMPGEnc has some other .ac3 software though.

But my original question(s) have all been beautifully answered so I'm happy. And I have a workflow that does fine, with the .ac3 transcoding happening inside Encore. Thanks all!

-- BC


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