Compressing Video for Streaming


This is a sneak peek at the script for our upcoming video on streaming. Look for a streamed version soon.

Part Four:


[ROLL TITLE:


The Compression Session]


 


Setting: Talent in editing bay with PC/TV, video equipment, and cables surrounding them


 


TALENT B:

The next step in making a video to be streamed is digitizing and compressing it on your computer. The first part is copying the video onto your hard drive so you can compress it to stream.

TALENT A:

If you are using standard VHS, S-VHS, or 8mm camcorders, you will need to buy a capture card. A video capture card is an expansion card that works in conjunction with or sometimes replaces the existing graphics adapter inside of your computer.

[SHOW CLIP OF CAMCORDER PLUGGING INTO CAPTURE CARD]


TALENT B:

It allows you to take video from an analog source and will convert it to a digital video format, recording it as a long stream of bits onto the hard-drive.

TALENT A:

There are three main formats that digital video uses. The first is MPEG. MPEG is an open standards format. The next is QuickTime MOV files. QuickTime is the proprietary format developed by Apple.

TALENT B:

The other major video format is the proprietary Video for Windows format used by Microsoft called AVI. Microsoft will soon replace the AVI with the new Advanced Streaming format or ASF. Some streaming packages work only with one of the video formats, while others can use two or all three of them.

TALENT A:

So make sure when you buy a capture card to buy one that can store video in the format that you need to use to match the streaming software that you want to use.


Most inexpensive capture cards use RCA adapters

[SHOW CLOSE-UP OF RCA ADAPTER PLUGGING INTO VCR]

to link the camcorder or VCR to the capture card. Some can also use S-video cables.

[SHOW CLOSE-UP OF S-VIDEO CABLE PLUGGING INTO VCR AND PC/TV]


TALENT B:

If you have a digital camcorder, it might have a connection called Firewire that will hook to your machine, if you have a Firewire capture card installed.

[SHOW CLOSE-UP OF FIREWIRE FROM CANON OPTURA HOOKING INTO PC/TV]


TALENT B:

Actually there are two compression steps to streaming video on the Internet. The first step is compressing the video into an AVI, MOV, or MPEG format to store on your hard drive. When you do this, compress it at the lowest compression ratio your system can handle for best quality picture. Don’t worry about the file size at this point, because you will have to compress the video again into the streamable format.

TALENT A:

When you compress the MPEG, MOV, or AVI into the streamable format you have to choose exactly how you want it compressed. The first thing you want to decide is how much of the video quality you want to sacrifice to make the video play better on the Internet.

TALENT B:

The three factors that make up the quality of a video are frame rate, color depth, and resolution. First, frame rate.

[SUPER GRAPHIC ACROSS BOTTOM OF SCREEN:


Frame Rate]


TALENT A:

Frame rate is the number of still images that make up one second of moving video image. At thirty frames per second, images seem to move fluidly and naturally.

[SUPER GRAPHIC ACROSS BOTTOM OF SCREEN:


TV=30 Frames per Second]

When a video is digitized to a frame rate of less than fifteen frames per second, it becomes noticeably jumpy.

[SHOW CLIP OF A VIDEO AT 15 FPS; SUPER GRAPHIC ACROSS BOTTOM OF SCREEN:


15 Frames per Second]


TALENT B:

Current phone and modem technology limits the frame rate to around 10 frames per second, so you might as well set 10 fps in your compression scheme.

[SHOW CLIP OF A VIDEO AT 10 FPS; SUPER GRAPHIC ACROSS BOTTOM OF SCREEN:


10 Frames per Second]


TALENT A:

If the video clip you want to stream to phone-connected viewers contains a lot of action, then limit the video to 7 frames per second to make up for the fact that the compression is going to have trouble dealing with all of the movement.

[SHOW CLIP OF A VIDEO AT 7 FPS; SUPER GRAPHIC ACROSS BOTTOM OF SCREEN:


7 Frames per Second]


TALENT B:

The second variable is color depth.

[SUPER GRAPHIC ACROSS BOTTOM OF SCREEN:


Color Depth]

Color depth is the number of bits of data the computer assigns to each pixel of the frame. When there are more bits of data assigned to color each pixel, there are more colors that can be emulated on the screen.

TALENT A:

Most video is either 8-bit 256 color,

[SHOW SCREEN SHOT OF VIDEO SHOT AT 256 COLOR WITH SUPER GRAPHIC ACROSS BOTTOM:


8-bit 256 color]

16 bit 64,000 color,

[SHOW SCREEN SHOT OF SAME VIDEO AT 16-BIT COLOR WITH SUPER GRAPHIC ACROSS BOTTOM:


16-bit 64,000 color]

or 24-bit 16.8 million color.

[SHOW SCREEN SHOT OF SAME VIDEO AT 24-BIT COLOR WITH SUPER GRAPHIC ACROSS BOTTOM:


24-bit 16,800,000 color]


TALENT B:

As you can see, 256-color video is very grainy and unsuitable for video. The 24-bit color is optimal, but because it greatly increases the size of the file to be streamed, you’ll want to settle for 16-bit color if you plan on streaming video to viewers connected through the telephone.

TALENT A:

The third factor in determining the visual quality of the picture is resolution.

[SUPER GRAPHIC ACROSS BOTTOM OF SCREEN:


Resolution]

Resolution in digital video is measured in number of pixels.

TALENT B:

The more pixels there are in your picture, the higher the resolution of the video. For example, if your video is at 640×480, you have 640 pixels across each of the 480 vertical lines of pixels.

TALENT A:

Video to be streamed over the Internet ranges from postage stamp video at 49×49

[SHOW SCREEN SHOT OF VIDEO AT 49×49 WITH SUPER GRAPHIC ACROSS BOTTOM:


49×49]

to160x120. This is the highest resolution you can stream to users connected through a telephone line at this time.

[SHOW SCREEN SHOT OF VIDEO AT 160×120 WITH SUPER GRAPHIC ACROSS BOTTOM:


160×120]

All the way up to 640×480 and beyond,

[SHOW SCREEN SHOT OF VIDEO AT 640×480 WITH SUPER GRAPHIC ACROSS BOTTOM:


640×480]

which is considered full-screen video.

TALENT B:

The last important variable to set when compressing your video clip is key frames. Key frames are frames that are marked for guaranteed transmission.

TALENT A:

This means that the key frames are important for basing estimations of movement by the compression software. Most programs will automatically choose for example, every tenth frame as a key frame.

TALENT B:

Many let you arbitrarily choose any frame to be a key frame. If your streaming software allows this, you should make sure that the first frame of any zoom, panning shot, or heavy movement scene is marked as a key frame.

TALENT A:

This will help the software properly guess what movement is going to happen, and will result in a smoother, more professional-looking streamed video.

TALENT B:

Some of the streaming programs will automatically set the color depth, frame rate, and resolution to match a certain connection speed.

TALENT A:

If your streaming software supports this, always set your target speed a little bit slower than what the connection is supposed to be at.

TALENT B:

For example, if you were compressing a video to be played on a modem, set the video to run at 24,000 bits per second rather than the 28,800 they are supposed to connect at.

TALENT A:

That way, if there is latency on the Internet, and there will be, your viewers won’t have as many pauses as the video is streaming just a little bit faster than the modem can receive the data.

TALENT B:

If you compress your video properly, it can be streamed to viewers with a variety of different connections. As we said, the factors you can adjust are Frame Rate, Color Depth, and Resolution. By properly adjusting these settings you can make your video so the modem users will have streamable video, while the higher-bandwidth users will have a larger picture, and more motion and color.

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