This IS the Avid L2: Re: [Avid-L2] Re: QC Issue with Interleave vs. discrete audio as I anticipated?

Tuesday, June 9, 2015

Re: [Avid-L2] Re: QC Issue with Interleave vs. discrete audio as I anticipated?

This is very helpful info. Now I can play along better.

---In avid-l2@yahoogroups.com, <bouke@...> wrote :

Acutally, i was wrong. A Wave file can be 4 gig. But some programs only accept two gig.

The reason:

There are 4 bytes reserved to describe the length of the file (in bytes).

Now that should written and read as a unsigned integer. (Meaning, it can only hold a positive value, and that makes sense, as a negative duration won't ever happen.)

Some programs read it as a signed integer, so one bit is to see if it's positive or negative, effectively half the amount of values possible in the 4 bytes.

(and that is 2 to the power of 32 = 4294967296 aka 4 gig. Another way to get to this number, get your calculator, switch to HEX and type in the 4 hightest bytes,

meaning FF FF FF FF, and convert to Decimal.

In quicktime, it's different.

The sound itself can be exactly the same, meaning PCM, just volume data without any compression / decoding needed, just read it and it will tell you how loud the current sample is.

PCM is nothing more than having uncompressed bytes describing the volume of the current sample.

The wrapper around it (either Wave, AIFF, MXF, QT) will tell the player where the sound acturally starts in the file, and tells the player about the format.

So, for PCM, there is no theoretical max length.

You can have 'raw' PCM, where there is only sound data.

But then you need to tell the player what to expect, (amount of channels, bit depth, sample rate) or it won't be able to play it back. Hence close to all formats have a header to set this.

(And that can be modified, doing lots of handy stuff, but also mess things up big time. (BWF support in FCP 7 as a major example).)

So, your 'interleaved' 1 Track 12 Channel sound lives in a QT file as the Wave file, minus the Wave header / footer. Exactly the same.

A 12 Track One channel (aka Poly in my terminology) will have all sound tracks after each other, inside one big QT file.

Iff you are not into coding or use a HEX editor to look at the files, it's impossible to know, you need programs like MediaInfo, VLC, QT pro to tell you the format.

Luckily, they are most of the time right.

Bouke

VideoToolShed
van Oldenbarneveltstraat 33
6512 AS NIJMEGEN, the Netherlands
+31 24 3553311

----- Original Message -----
From: bigfish@... [Avid-L2]
To: Avid-L2@yahoogroups.com
Sent: Tuesday, June 09, 2015 4:54 AM
Subject: Re: [Avid-L2] Re: QC Issue with Interleave vs. discrete audio as I anticipated?

Wow so a wave file can be no larger than 2GB. I'd always hated the 4GB omf export crap but that could be a pain for some really long project stems. Can't say I've hit that limit but most of my audio pass offs come from protools aafs these days for my in house work.

So when QT has a single track with 12 channels in it, which I'm calling interleaved, does that mean there is a Poly Wave file hiding under the hood somewhere? Or is the QT track and subchannels structure totally different than wave files mono or poly. When I do my QT ref export of the 12 channels from my timeline and then save as I get the 12 discrete Tracks that seem to be what the network wants. Now are those files after the save as in QT really mono wav files under the hood with a QT wrapper on top?

Even though big multitrack audio decks were maintenance intensive at least I could see where the audio really was. Now this darn digital voodoo makes things soooooo confusing. ;-(

---In avid-l2@yahoogroups.com, <bouke@...> wrote :

AFAIK, Mono and Poly comes from the BWF world.
(Due to the 2 gig file limit of Wave shooting mono is popular if you do long takes and/or multiple channels)

Interleaved might be the correct term for Wave files, but for Quicktime it's more complicated.
In a multi Channel / single Track the sound channelas are definitly interleaved, but that does not guarantee that the audio is interleaved with the video.
(If you paste a soundtrack in a movie and do a save as QT ref the sound is obviously NOT interleaved with the video)

That's why i don't like the term 'interleaved' for QT.
But, my 'mono' and 'poly' aren't industry terms either.

In QT lingo, it's 'channel' and 'track', where audio one track can have one or more multiple channels.
A QT file can have multiple tracks, and the tracks can contain audio, video or data.
(So you can have a QT file with 40 video tracks, 50 audio tracks where audio track 1 has 16 channels, audio track 2 has just one channel, you name it, it's possible.)

Bouke

VideoToolShed
van Oldenbarneveltstraat 33
6512 AS NIJMEGEN, the Netherlands
+31 24 3553311
----- Original Message -----
From: bigfish@... [Avid-L2]
To: Avid-L2@yahoogroups.com
Sent: Saturday, June 06, 2015 11:56 PM
Subject: Re: [Avid-L2] Re: QC Issue with Interleave vs. discrete audio as I anticipated?

I ended up going the QT Ref out and Save as. I know we went over the term interleave before. Is the Poly .wav different from interleaved?

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