For a project I have been working on I needed to incorporate videos. I found perfect videos at my favorite stock photo site iStockphoto (although much more pricey than the good old days). Here is where my complete lack of video knowledge starts to come into play!

The videos I found I wanted to use said they included an Alpha Channel Mask or Alpha Matte which I had found from a few great tutorials would cut out the video from the background and allow me to use the videos as overlays or talking heads with the rest of the video background being completly transparent.

I downloaded the video and proceeded to import it directly into Flash (it was a FLV already after all) but alas not only was it just a normal video without the Alpha Channel effect there was this black and white cutout section after the video. Going back to my complete lack of video knowledge I was really lost. I figured it was just because I didn’t have the actual file and just a proof. So, I downloaded an original file and imported that using the Flash Encode Alpha Channel setting. Still no Alpha Channel and Video Transparency (just now better quality and without the iStockPhoto watermark).

Below is the final workflow I arrived at to turn iStockphoto Video comps with attached Alpha Masks into Quick Time (.mov) movies with alpha channels and ultimately Flash Video (.flv) files with the alpha channel. I will be using Sony’s Vegas Movie Studio Platinum Version 8 and FLV to AVI MPEG WMV 3GP MP4 iPod Converter to make the magic happen. I will also go through how to transform the Green Screen (Chroma Key) videos into videos with alpha channels along the way.

STEP 1: Find your video on iStockphoto. You can search for “Alpha Channel” “Alpha Mask” or “Chroma Key” to find videos that contain the attached Alpha Masks or were shot on a Green/Blue Screen.
STEP 2: Click on the Video and then Select The Download a Comp link.
MPEG Converter
STEP 3: Follow my previous tutorial on converting Flash Video files to MPEG or MOV files.
STEP 4: Open Sony Vegas Movie Studio and Create a New Project. In the project setup select to match the project a video file and select the video file you created in Step 3.
Drag Video to Stage
STEP 5: Using the Explorer Window (one of the tabs at the bottom of the screen) find the movie file you created in Step 3 and drag the video file to the Video Timeline (The 3rd One Down).
STEP 6: If your Video has an Alpha Mask at the end of the video we next need to pull that out to use it. Drag the PlayHead to the last frame that has the video and the frame right before the Black and White Alpha Mask Section. Then Press the “S” key or select Edit – Split. You now have two clip pieces.
Split Mask From Video
STEP 7: Drag the Alpha Mask Clip (the one on the right) Up to the Video Overlay Stage Layer (one above the Video Layer).
STEP 8: Click on the Double Green Box and Change the Mode to “Mask”
Luminance Mask Selection
STEP 9: Click on the Video FX tab at the bottom of the page. Select “Mask Generator” From the list box on the left. Drag the Luminance Mask Effect up to the Alpha Mask Clip (the one in the Video Overlay Stage) then close the Popup Window
Luminance Alpha Channel Mask

At this point you now have your Alpha Mask and background of your video is transparent. If your video was shot on Green Screen sometimes the mask is off a bit and the Green Screen can show through. At this point you can through in a Chroma Key to get rid of the Green Screen

Chroma Key Green Screen
IF YOU HAVE A GREEN SCREEN: On the Video FX tab Select “Chroma Keyer”. Drag the Pure Green Screen Chroma Key effect to the Video Stage (the one with the main video … and the green screen)

STEP 10: Render the Video. Select “Render As” from the File Menu. I extracted it as a Quick Time 7 (*.mov) and set the quality to best. NOTE: You need to make sure that your CODEC supports Alpha Channels before you export otherwise … you are back to where you started.

The video now includes the Alpha Channel and you can use it in your Project. I imported my videos into Flash. If you are importing them into Flash you need to make sure you select Encode Alpha Channel in the video import properties.

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