Prototyping 2013-11-05 (Lens Based Media)

From XPUB & Lens-Based wiki

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, browsers etc)


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)


comparison of video codec

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)

Iframes.jpg

More Info
[1]

Encoding Tools

Bitrate + Framesize

Most lossy codecs allow you to set a bitrate (the amount of bits per second)
Together with the framesize this determines the quality of the video. Floppy Films

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? (Camera codec? DSLR)
  • How do you edit? (intermediate files?)
  • What do you deliver? (Archiving, uploading, DVD?)


Example, for editing/archiving use:

  • ProRes video codec (visually lossless through many iterations)
  • Wav/Aiff audio codec
  • .mov container

For (online) delivery use:

  • H.264 codec
  • MP3/ACC audio codec
  • .mp4 container


Glitch Art & Data moshing

Download Finished

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