video-codecs.md

Video codecs

A program capable of COmpressing and DECompressing certain formats.

The term is often used in phrases as: "Do you have the codec for XXX to watch" in which it means, do you have the program that does the decoding?

Trivia

https://en.wikipedia.org/wiki/Comparison_of_video_container_formats

History

http://stevencrowley.com/2012/08/14/new-video-compression-standard-doubles-efficiency/

CPU power also limits compression: a super encoded file is useless if CPUs / GPUs aren't fast enough to decode in real time.

H.264

MPEG-4 Part 10

Not free, dominates in 2015.

https://en.wikipedia.org/wiki/H.264/MPEG-4_AVC#Patent_licensing

One of the major implementations: http://www.videolan.org/developers/x264.html

Many profiles, which are parameters that determine how encoding / decoding is to be done exactly: https://en.wikipedia.org/wiki/H.264/MPEG-4_AVC#Profiles Algorithm changes widely between profiles.

MPEG LA patent pool.

Network Abstraction Layer

NAL Units

https://en.wikipedia.org/wiki/Network_Abstraction_Layer

http://stackoverflow.com/questions/6858991/in-h264-nal-units-means-frame

So it seems H.264 also specifies the stream format. Must it be followed, or can we just send chunks of any size?

Some libraries must be fed such variable sized pages to work (Android 5 MediaCodec), while others can just take fixed sized chunks and deal with it (FFmpeg doc/examples/decoding_encoding.c).

H.265

HEVC

Non-free proposed successor to H.264.

https://en.wikipedia.org/wiki/High_Efficiency_Video_Coding

MPEG LA patent pool.

VP8

VP9

Free, by Google, for the web.

Implemented by libvpx.

Daala

Free by Xiph and Mozilla.

https://xiph.org/daala/

Thor

https://en.wikipedia.org/wiki/Thor_%28video_codec%29

Free, by Cisco.

M-JPEG

Video version of JPEG.

https://en.wikipedia.org/wiki/Motion_JPEG

MPEG-1

https://en.wikipedia.org/wiki/MPEG-1

Looks like a codec, for both audio and video, which is often encapsulated into https://en.wikipedia.org/wiki/MPEG-4_Part_14 with extension .mpg or .mp4.

Extended from: JPEG, H.261

Extended to: MPEG-2.

MPEG-2

https://en.wikipedia.org/wiki/MPEG-2

H.222/H.262. TODO: why two names?

Extended from: MPEG-1.

Inferior to H.264.

Codec agnostic concepts

https://en.wikipedia.org/wiki/Video_compression_picture_types

• Intra-coded: key-frame.
• Predicted: uses previous. Some algorithms may use even more than 1 previous frame.
• Bi-predictive: uses previous and next