No alpha channels in any format when exporting mxf from avid xpress hd

[Michael Hancock]

You’ve found one big drawback in Avid–you can’t export anything with an alpha channel. You have to export the matte and fill seperately.

Since you’ve already keyed this in Avid:

First, export the keyed video in your sequence in whatever format you want it. You can do a targa or png sequence, a self contained quicktime, a quicktime reference (if you’re compositing on the same computer as your Avid), avi, whatever works for you. This is the Fill.

Depending on the keyer you use, there will be a button somewhere that lets you Show Matte. In some keyers it’s a button you turn on, in others it’s a menu item. When you turn this on it will give you the black and white image of your key–the Matte. Turn this on for all of the keyed clips in your sequence and export these.

You now have the Fill and Matte as seperate clips, outside the Avid. Take them into your favorite compositing program and use your Matte exports as a Luma Matte for the Fill. You should be good to go!

Let us know if you get stuck somewhere.

Michael.

PS. The link you provided above covers which codecs support Alpha channels when exporting from a program into Avid–say exporting from After Effects to take the files to Avid. Unfortunately, as I said above, Avid doesn’t export Alpha channels at all, even in their own codecs.

[Alyousha]

Hello, firstly thank you for the quick reply, secondly sometimes you need someone normally a pro to tell you its not possible to believe youre not doing something wrong somewhere… secondly its so disappointing that avid can’t export alpha channels.
I’m going to list couple of things i tried today to solve this problem just in case anyone thinks they got the soloution and before they go and waste time doing what i did, I captured two minutes of HD 1080i/50 on a final cut pro mac machine today then exported the footage as pal qt then as HDV and as a tiff sequence, when I transfered the footage to my PC the pal export worked fine but the quality obviously isnt high as HD, the tiff was of high quality but I didn’t like the colour depth, the HDV didn’t work; i get a footage in ae that has the same size of hd 1920 by 1080 but of a white screen (no images) the same thing happense when i changed the extention of the raw footage I captured in final cut to .mov (captured as HD) this used to work with DV pal/ntsc
the funny part of this is when I tried to play the HD raw footage and the exported HD qt in almighty qt 7 player it crashed lol
there’s seems to be a flaw in the HD code, they shouldn’t really make a big fuss about HD when its still in this state…
I will try the soloution you suggested and in addition I downloaded adobe premier trial (it always seems the old way rules even with modern technologies)to see if I can capture in HD and edit in AE, will let you know in the next few days how its going..
thanx a million for your feed back.

[Alyousha]

Ok, I Exported the matt and the fill, it wont work because if you set the luma key to brightness it will make the gaps that will expose the needed objects beneath but you still got the black area!!!! what they use for this effect I think is diffrence matt not luma key but you need an alpha channel for that, so we’re back at square one…
I used premier but it doesn’t have a preset for 1080i/50 but it has a preset for the rest of the HD, after searching the internet it turned out that there is plug in called cineform for premier… I used it and I can capture from it really nicely the only draw back is it creats really large files for HD (larger than Avid’s HD, secondly, every time you capture 10 seconds and stop cineform has to export the footage you captured frame by frame and it dose it so slowly… so 3 hourse will take something like 9-11 hours to capture if I’m not wrong and you have to be there every minute so your footage wont be something like 8GB for5 minutes..

[Michael Hancock]

Using the matte as a luma matte will work, but you might have to invert the luma matte.

Perhaps most importantly–what program are you trying to composite in? You said your footage was keyed in the Avid and you wanted to export it with an alpha. You never said where it’s next destination was–is it going to Premiere? Is it going to After Effects? Combustion? Shake? Where you’re sending it will make a difference in how you use the matte and fill.

Michael.

[Alyousha]

Hello,I’m exporting from Avid to after effects not sure if you meant inverting luma key by swiching from key brighter areas to darker or the oposite, if this is what you meant then i tried both and it wont work if you mean invert as in filter (red to blue kind of thing then I haven’t tried that!!!

[Erik Pontius]

Have you considered doing your keying in After Effects? A possible workflow might be to capture your HDV content in Avid, transcode the footage to DNxHD and export as a Quicktime Same as Source. Import your footage into AE (it will be 1920x1080i upper field first square pixels). Key your footage using keylight and then export out of AE to a codec that supports an alpha…or just continue doing the rest of your compositing.

Erik

[Joe Womble]

This makes sense if you are taking it to After Effects for your other compositing work. Another option would be to consider using Boris RED (Avid FX) for your keying. I have found the quality to be quite good for my greenscreen work. Boris will export movie files with straight or pre-multiplied alphas, as well.

Regards,

Joe Womble

[Michael Hancock]

alyousha,

You’re misunderstanding what I’m saying about using the matte as a luma matte. I’m not talking about applying a filter or an effect here–I’m taking about using it as a track matte.

In After Effects, import your Matte and Fill.

Make a new composition and drag the Matte and Fill to it, with the Matte above the Fill.

Assuming you’re using a default layout, look at your composition–you should see the eyeballs where you turn your layers on and off, then the source name of your layers, then the switches where you can change each layer from Full resolution to Draft, set a layer to shy mode, turn motion blur on for the layer, etc… This is the Switches column.

Hit F4 and the switches column will change to the Modes column and show your Transfer Modes and Track Matte options. You want to click on the pull down box of the Track Matte for your Fill layer and set it to either Luma Matte or Luma Inverted Matte, depending on what’s black and what’s white in the Matte layer above it.

After Effects will use the Matte layer, which is directly above the fill layer, as the Matte Key for the Fill layer. Any part of the Matte Layer that is 100% black will make the corresponding parts of the fill layer completely transparent, and any part of the Matte layer that is 100% white will make the corresponding parts of your fill layer opaque, and shades of grey will be semi-transparent.

This should key your footage. If you still have a little bit of a halo, precomp the Matte and Fill and add a Matte Choker, soften and adjust to taste, then finish your compositing.

Hopefully this made sense. It does work–I’ve done it with hundreds of clips. I get a better key in Avid using Ultimatte than I do in After Effects with Keylights. This is how I maintain that key in After Effects for the final compositing.

Let me know if this makes sense for you–also, look up Track Mattes in the After Effects help book/online help. It should explain it in further detail.

Michael.

[Alyousha]

Hey, ok i know now what to do in AE and the boris fx option sounds very interesting, I will try both of them and report back, can’t wait to try those methods, your feed back is very appreciated guys, thanks alot

[Chris Bresnahan]

I have the same basic problem. We shot a talking head in front of green, made QuickTime clips in Media Composer and sent the QT file to the Flash designer to integrate into a project. He asked if it was compressed with the alpha channel. Doing a little digging, I find that no, it was not compressed with the Alpha Chanel ( or ever will be I guess) Should I Export the “Show Matte” of the same sequence as a quick time, and ftp him that in addition so that he can do the composite? Thanks!