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Vste r2


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Vste r2

  1. 1. Video Compression Making BIG files small
  2. 2. What is Video Compression <ul><li>Most video compression is lossy, i.e. it operates on the premise that much of the data present before compression is not necessary. </li></ul><ul><li>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 </li></ul><ul><li>Video Compression is a trade off between video quality, disk space, and hardware needed for decompression </li></ul>
  3. 3. More about compression theory <ul><li>Video data contains spatial and temporal redundancy. </li></ul><ul><li>Spatial Data= Difference within frames </li></ul><ul><li>Temporal Data = Difference between frames </li></ul><ul><li>Interframe vs intraframe compression. </li></ul>
  4. 4. What went wrong?
  5. 5. What was wrong with that video? <ul><li>Interlaced </li></ul><ul><li>Data rate - 300kbs </li></ul><ul><li>Key frame - every 150f </li></ul><ul><li>Frame rate - 15fps </li></ul><ul><li>Quality Settings - High </li></ul><ul><li>Codec - H.264 </li></ul><ul><li>Size Ratio 480 x 360 - 4:3 </li></ul><ul><li>2MB Original-165MB </li></ul>
  6. 6. Interlaced VS Progressive <ul><li>NTSC = 29.97 interlaced frames of video per second </li></ul><ul><li>Interlaced=image is broken into odd and even lines </li></ul><ul><li>Progressive scan means every frame is the entire image </li></ul>
  7. 7. Interlaced compression artifacts
  8. 8. What is Data Rate? <ul><li>Data Rate is the number of bits that are conveyed or processed per unit of time </li></ul><ul><li>Data rate is synonymous with bit rate. </li></ul><ul><li>While often referred to as &quot;speed&quot;, Data rate does not measure distance/time but quantity/time </li></ul><ul><li>Data rate includes video and audio combined </li></ul><ul><li>Video(300kbs) + Audio(128kbs)= </li></ul><ul><li>Total Data Rate(428kbs) </li></ul>
  9. 9. Data Rate <ul><li>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. </li></ul><ul><li>-Some computers cannot handle higher data rates </li></ul><ul><li>-Think about how your audience will retrieve your video and let the software do the work </li></ul>
  10. 10. Key frames <ul><li>In video compression, a key frame is a frame that contains the entire image </li></ul><ul><li>Difference frame or in-betweens contain only important info to fill in the gaps between Key Frames </li></ul><ul><li>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. </li></ul>
  11. 11. Key frames
  12. 12. Key frames <ul><li>More action needs more key frames </li></ul><ul><li>Running video looks better at a setting of every 60 frames </li></ul><ul><li>Fish still looks good at every 150 frames </li></ul><ul><li>Always adjust key frames when compressing </li></ul>
  13. 13. What is Frame Rate <ul><li>The frame rate is the number of frames per second displayed during the video. </li></ul><ul><li>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 </li></ul><ul><li>Basically, a frame is the same as a still picture </li></ul>
  14. 14. Frame Rate <ul><li>Most camcorders record at 30fps </li></ul><ul><li>Progressive mode is usually 24fps </li></ul><ul><li>Film is 24fps </li></ul><ul><li>NTSC is 29.97fps and Pal is 24fps </li></ul><ul><li>Adjust by halfs 30-15fps 24-12fps </li></ul>
  15. 15. Quality Settings <ul><li>The quality factor of encoded video streams is a rough measurement of video encoding quality expressed in bits per pixel. </li></ul><ul><li>Most programs let you adjust compressor quality </li></ul><ul><li>Start low and work up </li></ul>
  16. 16. Codec <ul><li>A video codec is a device or software that enables video compression and/or decompression for digital video. </li></ul><ul><li>Co = Compressor / Dec = Decompressor </li></ul><ul><li>Most widley used codec currently for video is H.264 (MPEG4 Ver10) </li></ul><ul><li>Other examples, H.261, MPEG-1 thru 4, H.263, DivX, Xvid, WMV and the list goes on and on </li></ul>
  17. 17. Size <ul><li>This greatly impacts file size and quality </li></ul><ul><li>Try 480x340 for 4:3 SD </li></ul><ul><li>480x270 for 16:9 HD </li></ul><ul><li>NTSC is 640x480 </li></ul>
  18. 18. Audio Settings <ul><li>Always set to mono, at this level of compression you gain little from stereo </li></ul><ul><li>Encode using AAC </li></ul><ul><li>Set to 22.050khz </li></ul><ul><li>Set target bit rate to 48kbs </li></ul>
  19. 19. Looking Good! <ul><li>Progressive </li></ul><ul><li>Data rate - Auto </li></ul><ul><li>Key frame - every 60f </li></ul><ul><li>Frame rate - 15fps </li></ul><ul><li>Quality Settings - Med </li></ul><ul><li>Codec - H.264 </li></ul><ul><li>Size Ratio 480 x 360 - 4:3 </li></ul><ul><li>8.6MB Original 165MB </li></ul>
  20. 20. Looking Good!
  21. 21. Sample Video Comparison <ul><li>Interlaced </li></ul><ul><li>Data rate - 300kbs </li></ul><ul><li>Key frame - every 150f </li></ul><ul><li>Frame rate - 15fps </li></ul><ul><li>Quality Settings - High </li></ul><ul><li>Codec - H.264 </li></ul><ul><li>Size Ratio 480 x 360 - 4:3 </li></ul><ul><li>2MB Original-165MB </li></ul><ul><li>Progressive </li></ul><ul><li>Data rate - Auto </li></ul><ul><li>Key frame - every 60f </li></ul><ul><li>Frame rate - 15fps </li></ul><ul><li>Quality Settings - Med </li></ul><ul><li>Codec - H.264 </li></ul><ul><li>Size Ratio 480 x 360 - 4:3 </li></ul><ul><li>8.6MB Original 165MB </li></ul>
  22. 22. What programs can I use? <ul><li>Sorenson Squeeze </li></ul><ul><li>Flash Media Encoder </li></ul><ul><li>Quicktime Pro </li></ul><ul><li>Compression is built into ,most major editing packages I.E. Final Cut, I-movie, Adobe Premier </li></ul>
  23. 23. File Types <ul><li>Flash FLV </li></ul><ul><li>Quicktime MOV </li></ul><ul><li>Realplayer .ra, .rax, .rv., .rvx, .rm, .rmx, .rmj, .rms </li></ul><ul><li>Windows Media Formats .asf, .wma, .wmv, .wm </li></ul>
  24. 24. Thank You For Coming <ul><li>Now for Examples </li></ul><ul><li>[email_address] </li></ul><ul><li>[email_address] </li></ul><ul><li>www.k12albemarle.org </li></ul>