Prepared byLarry KlessKaiser PermanenteJanuary 22, 2008

What Producers Need to Know AboutVIDEO COMPRESSION

Producers need to know about

Video compression Data rates Video codecs vs. container formats Format considerations Progressive download vs. Streaming Optimal quality settings Shooting tips for web video

What is Video compression?

Video compression is the process of reducing the quantity of data used to represent video images

It’s a straight forward combination of image compression and motion compensation

It gets rid of redundant information of the video file which dramatically reduces the storage and bandwidth requirements

Video quality is reduced as the file is more compressed

Compressed video is encoded using a codec (coder-decoder) and is saved in container format (.mov, .flv, .wmv, .m4v, mp4)

What is Data Rate? Data rate (also known as bit rate) is the amount data that is transferred

per second

Described in Kilobits per seconds (Kbps) or Megabits per second (Mbps)

For smooth video playback, data rate must conform to the the amount of available bandwidth e.g. size of the pipe or stored on physical media (CD or DVD)

Higher data rate = less video compression Results in higher quality video resolution

Lower data rate = more video compression Results in lower quality video resolution, especially with motion

Compression BasicsWhy Should Producers Care?

The most important point to remember when producing video for the web is that any motion degrades video quality

For web video, keep in mind amount of bandwidth (or connection speed) that’s available to your viewers controls their ability to retrieve and play video smoothly

You may need to create a high and low quality version to accommodate your audience

Codecs vs. Containers

Codecs (compression) DV/DVCPRO Sorenson Spark On2 VP6-S H.264 MP3, AAC (audio)

Container (file format) MOV FLV MP4V, M4V 3GP, 3G2 (mobile) MP3, M4A, MP4 (audio)

Example “I’m creating a FLV file using the Sorenson Spark codec compressed at 448 Kbps for my client’s web site”

Choosing a FormatMakes no difference if you don’t know *

Who your audience is What do they want to see How do they want to see it What’s the business application

Other considerations include Complexity of the content (motion, background lighting) Desired reach (internal or external) Ability to archive (high quality master) Licensing considerations (Talent licensing? Broadcast licensing?

Streaming server? Digital rights management?)* Acknowledgement to Dan Rayburn

Progressive Download vs. Streaming

Progressive Download Available within KP Uses a regular web server No hosting costs since files are on KP

servers On-demand only Content can be compressed to any

data rate Can be easily upload to any web

server Video data must load before you can

skip to the end of clip Very difficult to capture any viewing

metrics (page clicks at most)

Streaming Not available within KP Uses a special streaming server Cost varies based on hosting

service (approx. $300/mo.) Both live and on-demand Content must conform to available

bandwidth Outsourced to streaming service

provider You can skip around to any point

of the video Can capture robust viewing

metrics

Optimal Quality Settings Flash Video

Medium quality (current standard) Encode video for Flash 7 player Video codec: On2 VP6 Video data rate: 300 Kbps Audio codec: MPEG Layer III Audio data rate: 64 Kbps Advanced settings: 30 Fps, Aspect ratio: 320x240 pixels, Key frame placement: Automatic

High quality Encode video for Flash 7 player Video codec: On2 VP6 Video data rate: 448 Kbps (For higher motion video use 700 Kbps) Audio codec: MPEG Layer III Audio data rate: 64 Kbps Advanced settings: 30 Fps, Aspect ratio: 480x360 pixels, Key frame placement: Automatic

Shooting for Web VideoFour Need to Knows

1. Watch the amount of motion as it degrades the quality of the compressed video. Limit camera motion. Multiple cuts from shot to shot compress at much higher quality than panning, zooming or dissolves.

2. Manage your backgrounds carefully. Codecs respond differently to different backgrounds. The best backgrounds have no motion and low detail. Don’t use high contrast colors or wide open spaces, break up the background with some texture.

3. Lighting is key. Compression decreases overall contrast, so use soft lights to reduce artifacts and noise during compression. You have to avoid gain noise in the camera, and create adequate contrast between the subject and the background. Both 3-point and flat lighting work well for web video.

4. When possible, shoot in progressive mode vs. interlaced.

For More Information

Larry.Kless@kp.orgProduction Manager, VideoconferencingMultimedia CommunicationsKaiser Foundation Health Plan, Inc.1950 Franklin, 3rd FloorOakland, CA 94612Tel: (510) 987-3956Cell: (510) 847-4286