## Compression vidéo
### Applications aux médias interactifs
#### Guillaume Arseneault
[gllmar.github.io/slides/compression_video](/slides/compression_video/#/)
#### octobre 2017
## Plan
* Signaux, résolutions et ratios
* Débit, cadence et trame
* Containers vs codecs
* Compression
* Lossy/lossless
* Intraframe et Interframe
* Usages spécifiques
* Questions/commentaires et ...?
## Signaux, résolutions & ratios
* [Signaux analogues/digitaux](https://en.wikipedia.org/wiki/Video#Analog_video)
* [transmission télévisuelle analogue](https://en.wikipedia.org/wiki/Analog_television)
* [résolutions](https://en.wikipedia.org/wiki/Computer_display_standard#/media/File:Vector_Video_Standards2.svg)
* [ratios image](https://en.wikipedia.org/wiki/Display_aspect_ratio)
* [ratios-pixels](https://en.wikipedia.org/wiki/Pixel_aspect_ratio)
## Débit, cadence et trame
* [Débit (bitrate)](https://en.wikipedia.org/wiki/Bit_rate#Video)
* Profondeur de l'échantillonnage couleur
* [bit/canal](https://en.wikipedia.org/wiki/Color_depth)
* [chroma subsampling](https://en.wikipedia.org/wiki/Chroma_subsampling#Sampling_systems_and_ratios)
* [4:4:4 vs 4:2:2 vs 4:2:0](https://upload.wikimedia.org/wikipedia/commons/0/06/Colorcomp.jpg)
* [4:4:4 vs 4:4:4:4](https://en.wikipedia.org/wiki/Alpha_compositing)
* [Cadence](https://frames-per-second.appspot.com)
* [Trame (progressif/entrelacé)](https://web.archive.org/web/20140222010640/http://neuron2.net/LVG/interlacing.html)
* [calcul de grosseur de fichier](https://toolstud.io/video/filesize.php?imagewidth=1920&imageheight=1080&framerate=29.97&timeduration=60&timeunit=seconds)
* [calcul de bitrate](https://toolstud.io/video/bitrate.php?imagewidth=1&imageheight=1&colordepth=24&framerate=29.97)
## Container/Codec
## Containers
| nom | extension |
| - | -|
| QuickTime | .mov |
| Matroska | .mkv |
| Mpeg4 | .mp4 |
| Windows Media Video | .wmv |
| Audio Video Interleaved | .avi |
| Theora | .ogv |
[wiki:Comparison_of_video_container_formats](https://en.wikipedia.org/wiki/Comparison_of_video_container_formats)
## Codecs
|Codec | compression | usage |
| - | - | - |
| H.264&VP8 | intra & inter | lecture<1080p |
| HEVC&VP9 | intra & inter | lecture<4k |
| proRes | intra | montage |
| dnxHD | intra | montage |
| HAP | intra | GPU&SSD :) |
## lossless/lossy Codecs
* [Encodage vidéo sans perte - lossless](https://en.wikipedia.org/wiki/List_of_codecs#Lossless_video_compression)
* Apple Animation (QuickTime RLE)
* CinemaDNG Raw (Adobe, Blackmagic)
* séquence d'images (tiff, openexr)
* [Encodage vidéo avec perte -lossy](https://en.wikipedia.org/wiki/List_of_codecs#Lossy_compression_2)
* H.264&VP8
* HEVC&VP9
* proRes, dnxHD, cineform
* HAP & HAPQ
## intraframe compression
* Toute l'image individuellement compressée dans chaque image.
* prores, dnxHD, photoJpeg, Apple intermediate codec (aic), cineform
* lossy demo?
### [interframe](https://en.wikipedia.org/wiki/Inter_frame)
* image temporellement compressée, [ce qui change](http://dvd-hq.info/data_compression_3.php)
* [images: I (clef), P (<-) et B(<->)](https://en.wikipedia.org/wiki/Video_compression_picture_types)
* [GOP : group of picture](https://en.wikipedia.org/wiki/Inter_frame#/media/File:IPB_images_sequence.png)
* usage créatif [1](https://www.youtube.com/watch?v=rMSsw4CZvKg), [2](https://www.youtube.com/watch?v=rSmEOk5AiN0), [3](https://www.youtube.com/watch?v=dNa0-xrKi3Q)
Usages
### compression intra et inter image
comme: H264, H265, vp8, vp9 etc...
* Capture
* Certain dslr, caméra abordable.
* favoriser l'option all-i si disponible
* Livrable/échange pour diffusion
* Archivage
* Lecture unidirectionnelle (vers l'avant)
* Streaming ([Vimeo](https://vimeo.com/help/compression), [YouTube](https://support.google.com/youtube/answer/1722171?hl=en) etc.)
Usages
### compression uniquement intra image
comme: prores, dnxhd, [redcode](http://www.red.com/learn/red-101/redcode-file-format) etc...
* capture
* (certains enregistreur et caméra haut de gamme)
* édition vidéo
* colorimétrie
* livrable/échange entre monteurs
Usages
## décompression optimisée GPU
comme : [HAP & HAPq](http://vdmx.vidvox.net/blog/hap) ou [dxv](https://resolume.com/software/codec)
* lecture multicouche
* haute résolution
* effets GPU
* requiert une carte graphique(vram) et un SSD rapide
## hap : [codec open-source](https://github.com/Vidvox/hap)
Compatible:
* [TouchDesigner](http://www.derivative.ca/wiki088/index.php?title=Hap)
* [max](https://cycling74.com/forums/announcing-hap-video-engine/)
* [OpenFrameworks](https://github.com/bangnoise/ofxHapPlayer)
* modul8, vdmx, madmapper, unity, isadora etc...
* [encoder avFoundation](https://github.com/Vidvox/hap-in-avfoundation/releases)
Médiagraphie
### Guides sur la compression vidéo
* [Vimeo-compression-basic](https://vimeo.com/blog/post/video-compression-basics)
* [B&H crash course sur les codecs](https://www.youtube.com/watch?v=sisvOeZItb0)
* [techquickie sur la vidéo compressé](https://www.youtube.com/watch?v=qbGQBT2Vwvc)
* [techquickie sur interlace/prograssif](https://www.youtube.com/watch?v=H_o5h5SK_70)
Médiagraphie
### Pour aller plus loin
* [Why Snow and Confetti Ruin YouTube Video Quality](https://www.youtube.com/watch?v=r6Rp-uo6HmI)
* [h264 vs h265](https://www.youtube.com/watch?v=Fawcboio6g4)
* [Videomaker introduction génerale](https://www.youtube.com/watch?v=fLlkgTRZSzc)
* [Vidéomake : bitrate ](https://www.youtube.com/watch?v=QOn-9anLFxA)
* [broadcast analogue avec esp8266](https://www.youtube.com/watch?v=SSiRkpgwVKY)
* [how-to datamosh](https://www.youtube.com/watch?v=tYytVzbPky8)
## Guillaume Arseneault
### [gllmar.github.io](https://gllmar.github.io)
### [gllm@artificiel.org](mailto:guillaume@artificiel.org)