Prototyping 2013-11-05 (Lens Based Media)

Compression & Codecs in video

(File)Format or Container is the shipping box, codec is the goods inside the box.

Format

• determines the way audio and video streams (and other metadata(like the codec info)) are stored inside the file
• Examples are :
  • .avi (Microsoft -> OLD)
  • .wmf (Microsoft -> Unflexible)
  • .mov (Apple -> supports a lot of codecs)
  • .ogg (Open Source -> but not very well supported by editing software)
  • .mkv (Open Source -> but not very well supported by editing software)
  • .mp4 (works on virtually all platforms)

intra- vs. interframe compression

Encoding/Compressing

Why do we compress?

• Image- and videofile sizes reduced
• More files to store, or longer videos
• Faster to download
• Downside: someone has to decode!

jpeg compression

Types of compression'

• Intraframe or spatial compression
  • Compresses each frame (so similar to image compression, with for instance JPG)
  • No effective size compression
  • High Quality
  • Easily readable by edit software
  • Apple ProRes, DNxHD (Avid)

• Interframe or temporal Compression
  • Compress BETWEEN frames
  • effective size compression
  • Not easy for edit software
  • Use for sharing -> final output
  • MPEG-2 (DVD's, hardware players), DivX (downloads), H264 (currently has best quality vs. file ratio)

encoding techniques

• Run length encoding > Looks for identical segments (often lossless)
• Transform coding > Most used (jpeg, DCT, wavelet) (selectively removes ‘non-relevant’ detail from the image).
• Chroma subsampling >Selective loss of resolution (4:4:4 vs 4:2:0)
• Reducing bit-depth (reducing colour accuracy)
• Fractal compression (replacing pixels with mathematic approximations)

More Info
[1]

Encoding Tools

• ffmpeg (ffmpegX for a Mac gui version)
• Mencoder
• Handbrake
• Mpegstreamclip
• Adobe Media Encoder

Workflow, Archiving & Delivery

There's no solution to the question 'What is the best setting for my video?". All depends on the platform you will deliver to!

• How do you record?
• How do you edit?
• What do you deliver?

• what happens when you upload to youtube?

Glitch Art & Data moshing

Download Finished

• How to datamosh
• Download Finished by Mediengruppe Bitnik
• glitch your image, source code

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