Vste r2

Video Compression

Making BIG files small

What is Video Compression Most video compression is lossy, i.e. it operates on

the premise that much of the data present before compression is not necessary.

For example, DVDs use a video coding standard called MPEG-2 that can compress ~2 hours of video data by 15 to 30 times while still producing a picture quality that is generally considered high quality for standard-definition video

Video Compression is a trade off between video quality, disk space, and hardware needed for decompression

More about compression theory

Video data contains spatial and temporal redundancy.

Spatial Data= Difference within frames Temporal Data = Difference between

framesInterframe vs intraframe compression.

What went wrong?

QuickTime™ and aH.264 decompressor

are needed to see this picture.

What was wrong with that video?

Interlaced Data rate - 300kbs Key frame - every 150f Frame rate - 15fps Quality Settings - High Codec - H.264 Size Ratio 480 x 360 - 4:3 2MB Original-165MB

Interlaced VS Progressive

NTSC = 29.97 interlaced frames of video per second

Interlaced=image is broken into odd and even lines

Progressive scan means every frame is the entire image

Interlaced compression artifacts

QuickTime™ and aH.264 decompressor

are needed to see this picture.

What is Data Rate? Data Rate is the number of bits that are

conveyed or processed per unit of time Data rate is synonymous with bit rate. While often referred to as "speed", Data rate

does not measure distance/time but quantity/time

Data rate includes video and audio combined Video(300kbs) + Audio(128kbs)=

Total Data Rate(428kbs)

Data Rate

Data rate greatly impacts quality of the video as well as size. I usually start with the automatic settings built into most current programs. Rule of thumb 300kbs for med-high bandwidth streaming 100kbs for dial up.

-Some computers cannot handle higher data rates

-Think about how your audience will retrieve your video and let the software do the work

Key framesIn video compression, a key frame is a

frame that contains the entire imageDifference frame or in-betweens contain

only important info to fill in the gaps between Key Frames

Think of an image of a person walking in front of a wall. To show motion only the person needs to be redrawn as the wall stays the same.

Key frames

Key frames

More action needs more key framesRunning video looks better at a setting

of every 60 framesFish still looks good at every 150 framesAlways adjust key frames when

compressing

What is Frame Rate

The frame rate is the number of frames per second displayed during the video.

More frames do not necessarily make the video look better, due to the limitations of the human eyes and brain to process all of the data

Basically, a frame is the same as a still picture

Frame Rate

Most camcorders record at 30fpsProgressive mode is usually 24fpsFilm is 24fpsNTSC is 29.97fps and Pal is 24fpsAdjust by halfs 30-15fps 24-12fps

Quality Settings

The quality factor of encoded video streams is a rough measurement of video encoding quality expressed in bits per pixel.

Most programs let you adjust compressor quality

Start low and work up

Codec A video codec is a device or software that

enables video compression and/or decompression for digital video.

Co = Compressor / Dec = Decompressor Most widley used codec currently for video is

H.264 (MPEG4 Ver10) Other examples, H.261, MPEG-1 thru 4,

H.263, DivX, Xvid, WMV and the list goes on and on

Size

This greatly impacts file size and qualityTry 480x340 for 4:3 SD480x270 for 16:9 HDNTSC is 640x480

Audio Settings

Always set to mono, at this level of compression you gain little from stereo

Encode using AACSet to 22.050khzSet target bit rate to 48kbs

Looking Good!

ProgressiveData rate - AutoKey frame - every 60fFrame rate - 15fpsQuality Settings - MedCodec - H.264Size Ratio 480 x 360 - 4:38.6MB Original 165MB

Looking Good!

QuickTime™ and aH.264 decompressor

are needed to see this picture.

Sample Video Comparison Interlaced Data rate - 300kbs Key frame - every 150f Frame rate - 15fps Quality Settings - High Codec - H.264 Size Ratio 480 x 360 -

4:3 2MB Original-165MB

Progressive Data rate - Auto Key frame - every 60f Frame rate - 15fps Quality Settings - Med Codec - H.264 Size Ratio 480 x 360 -

4:3 8.6MB Original 165MB

What programs can I use?

Sorenson SqueezeFlash Media EncoderQuicktime ProCompression is built into ,most major

editing packages I.E. Final Cut, I-movie, Adobe Premier

File Types

Flash FLVQuicktime MOVRealplayer .ra, .rax, .rv., .rvx, .rm, .rmx,

.rmj, .rmsWindows Media

Formats .asf, .wma, .wmv, .wm

Thank You For Coming

Now for Examples

[email protected]@k12albemarle.orgwww.k12albemarle.org