Is Multiplexing BAD?

[bayaraa_us]

HELLO

I was converting video files and creating DVD using DVD Workshop.
My Video and Audio files are in Elementary streams.
DVD Workshop is "Multiplexing" the video and audio files.

Is "Multiplexing" same as reconverting? Do I lose any quality?

[lordsmurf]

No.

[solarfox]

Way to give an informative answer, Smurf.

bayaraa -- "Multiplexing", in general, is simply the process of weaving the elemental streams into a single MPEG that contains all of the streams within it. More specifically, when it comes to DVD authoring, it's weaving the audio, video, and subtitle streams, along with certain DVD control data, into a single set of VOB files which contain everything necessary for playback. It's a necessary part of the process, so it will always take place when you go to author a DVD. But no, there's no reencoding going on, so you won't lose anything.

[daamon]

"Mulitplexing" - Also known as "mux" or "muxing"...

P.S. Way to give an informative answer, solarfax ("said" in a non-sarcastic tone...)

[freestyler]

multiplexing puts streams together
demultiplexing takes streams apart

to prove that your content is not being re-encoded you can always demultiplex your authored content and see for yourself that your files haven't been tampered with

tools that can demultiplex: dvd decrypter, vobrator, others...

[bayaraa_us]

Thanks guys

[lordsmurf]

Way to give an informative answer, Smurf. .

It answered the question. Short and direct.

[Brent212]

I know multiplexing isn't supposed to affect the quality of the video and audio streams, but I've noticed it can in fact change the video slightly. I made a post (here) about this, with pictures. All I did was take an mpeg file, demux and then remux it with Womble, and then compare screen caps. It's not re-encoding or transcoding it, but the color has changed noticeably as a result of the muxing process. My theory (could be completely wrong) is that the contrast was increased. It's enough that you can even tell when the two mpeg files are being played next to one another, and very noticeable if you open up both screen caps and do what I like to call "the alt-tab comparison".

I know that multiplexing can screw with the synch of the audio and video streams, but I've never read about it changing the visual attributes of the video stream. But then again, I've never read about anyone actually doing a test to check for this either.

[lordsmurf]

No.

[freestyler]

The original poster is talking about DVD-complaint multiplexing of elementary assets.

Different standards may apply to Womble's program-stream multiplexing.

[anzimike]

Dvd Workshop does have an encoder built-in and will automatically re-encode any noncompliant video to a compliant stream resulting in quality loss, but compliant streams. If your original video is a dvd-compliant resolution and you checked "do not convert compliant files" then ws probably will not reencode, but I've found ws to be a bit quirky and sometimes has a mind of its own. The act of muxing as answered above should not affect video quality in any way.

[Brent212]

No.

haha... that's redick. Smurftacular answer! But... what yes or no question was this directed at? Actually, was there a question mark in my entire message? I was mainly looking for either similar experiences or an explanation for why the video was changed, although I didn't actually ask for either... just seems like those would be the two natural responses.

@freestyler - I was just posting in this thread because everyone was discussing the effect of multiplexing, and it seems like a common (apparantly mis)conception that it doesn't alter the streams being worked on. Or at least that was a misconception I had anyway. I always thought that demultiplexing did nothing more than separate streams and that multiplexing did nothing more than put two or more streams together and add in "header" (not sure what the correct term would be) information.

[Josef K]

No.

So, here I am quickly scanning through these posts in this topic to see if there's anything I can explain which hasn't already been said...

It seems like things have been covered - except for one thing:

Why does that person keep posting all over this forum uttering just a single, solitary word. Is this some new form of deity on which every word we must hang? Is this what they call 'mysticism'?

Seriously, though. Give an explanation. A few words or so. Having a quick scan at the post previous to your second 'no', I'd have to read it all to see what you're replying to.

@freestyler I always seem to pause to take a sip of my drink, or lie back in my chair and relax for a moment when I see your avatar. Better than that bloke you had there before...

Disclaimer: If anyone reads this in the future and freestyler has changed his avatar back to 'that bloke he used to have there before' then I'm referring to the time when he had Lacey Nicole Chabert's gorgeous face there instead.

[Brent212]

Yes, I completely agree about the avatar. So nice.

[jimmalenko]

Nobody likes a threadjacker

[freestyler]

Hehe. Everyone loves the avatar

Thanks fellas, I'm glad it promotes peace

That bloke I had there was the opposite of peace (Al Pacino in "Scarface")

[Brent212]

Am I the thread jacker? If so, I only posted in this thread because it was dead and about a topic closely related to what I wanted to post about. I could have started a new thread, but I usually do a search and check the most recent couple of pages in the appropriate forum before doing that, because I know it's annoying to have a bunch of redundant topics (i.e. "What's your favorite authoring program?").

[freestyler]

This thread seems civil. Where is the TJ?

Have you got any Womble screenshots laying around still Brent?

[Brent212]

Yes. They are in my earlier post here:
https://www.videohelp.com/forum/viewtopic.php?t=248815

[Cornucopia]

I might have figured it out...

Take an mpeg file and demux it.
Save as Original.m2v
Take elementary files and remux with Womble, TMPGEnc, etc.
Demux that.
Save as Remuxed.m2v

Open each in Bitrate Viewer, DVDPatcher, ReStream, PVAStrumento, or something else that can analyze and explain settings for MPEG2.

Could be that a flag for color system is getting changed. That is, 1st it was set for CCIR601 color/brightness levels. Later gets changed to RGB levels. Even though the raw data isn't changed, the header may be.
Could also be in the "Play Sequence Descriptor Extension".

Just a guess/hope.

Scott

[Brent212]

Yes, that is exactly the type of thing that I thought was probably happening. Seems to be the most reasonable explanation.

[vhelp]

TGIF everyone :P

From my experience with working in this area, I have never seen any
issues so far. In fact, and depending on the deMUXer in use, you
might even benefit from it, much like a refresh like webpages
but w/ clean values in the MPEG source file. For example, bbMPEG
can be used to reMUX your source file w/ better mpeg attributes or
pre prep for DVD. But, I don't know how "grainish" that is, being
these days, your dvd autoring app(s) are suppose to give you best
results/values/attributes for your given MPEG source file(s)
.
I think I may be speaking for MPEG-2 in general (w/ regards to the
above suggestion) For instance, when people would refresh their
MPEG's in preporation (pre prep) for VCD, SVCD or DVD buring (or
now refered to as Authoring)

A year ago, I created a front-end (gui) to bbMPEG for this sort of
thing. But, it was (the tool) developed for a particular MPEG refresh
in mind.. and wouldn't serve you well here

* About Computer Programming...

-vhelp 2909

[Josef K]

That bloke I had there was the opposite of peace (Al Pacino in "Scarface")

That's him! I knew I knew him from somewhere...

P.S. Don't ever change the avatar!

/followups to Off Topic...

[jimmalenko]

This thread seems civil. Where is the TJ?

Brent212. Already started a thread of his own about his problem, yet jacks this one to be about it as well.

No biggie, just an observation

[lifesajrny]

No.

[lordsmurf]

I know multiplexing isn't supposed to affect the quality of the video and audio streams, but I've noticed it can in fact change the video slightly. I made a post (here) about this, with pictures. All I did was take an mpeg file, demux and then remux it with Womble, and then compare screen caps. It's not re-encoding or transcoding it, but the color has changed noticeably as a result of the muxing process. My theory (could be completely wrong) is that the contrast was increased. It's enough that you can even tell when the two mpeg files are being played next to one another, and very noticeable if you open up both screen caps and do what I like to call "the alt-tab comparison".

I know that multiplexing can screw with the synch of the audio and video streams, but I've never read about it changing the visual attributes of the video stream. But then again, I've never read about anyone actually doing a test to check for this either.

At your request, I'm giving a detailed response. While this may come off rude, it's not intended that way... not at all...

Sometimes it's hard to respond to things like this. Very reminscent of people that claim "my VCD looks better than the original DVD". In a situation like this, something is very obviously wrong with the viewing equipment. The claims go against the known tech.

I have no doubts that your problem is genuine. But the conclusion is flawed. Let me illustrate:

John likes blue.
John likes bananas.
Bananas must be blue.

.... and if you heard something like that, either aloud or in your head, you'd be thinking "what the f--- is this nonsense?"...

Mux/demux is not a procress that touches your video. It separates the streams, it does not augment them. Demux can no more change the color of a video than it can change the volume or tone of your audio. That's just not how things work.

More common, you have other issues, and you should seek them out.

For example, PowerDVD on one of my computers adds hiss to MP2 audio ... hiss that does not really exist. It also takes screencaps too dark, and will play M2V demuxed video darker than it should. VRO files will be washed out both in Womble and PowerDVD, but not to the authoring software or the DVD player. But it's because the software player is screwed. The actual files do not appear this way in the editor or on tv.

My knee-jerk reaction to this post what something along the lines of "hhhhhhhhhhuh? wtf is he talking about.. NO.. just..just NO" ... of which only the last word made it in print.

Hope this sheds light on things.

The RGB/YUV header, suggested by vhelp ... if such a thing exists ... may be worth looking into. At very least, it means your exact version of that exact program has a flaw.

[trock]

Brent, your 2 images in the other thread really do look like the CCIR601 setting has changed somewhere along the way. Different MPEG decoders differ in how they handle CCIR601 black levels but I haven't heard of demuxers or muxers doing so (doesn't mean that some may not).