This document discusses codecs and containers for digital video and audio files. It explains that a codec is an algorithm used to encode and decode media files, and containers hold encoded audio and video streams. It notes that to play a file, the correct codec and sometimes container format must be supported. The document provides guidance on determining which codecs are installed, identifying the codec used to encode a file, and adding codecs to common media players and editing software. It also discusses web streaming protocols.

1. What Is a Codec?
Or, Everything You Wanted to Know About Digital Streaming
Video But Were Afraid to Ask

2. What we’re NOT going to talk
about:
 The history of the moving image and recorded sound
FlipbooksZoetropeMoviesPhonoTalkiesTV
http://en.wikipedia.org/wiki/Film
http://en.wikipedia.org/wiki/Audio_recording
http://en.wikipedia.org/wiki/Television

3. What we’re NOT going to talk
about:
 The Nyquist-Shannon Sampling Theorem
“…shows that a bandlimited analog signal that has been
sampled can be perfectly reconstructed from an infinite
sequence of samples if the sampling rate exceeds 2B
samples per second, where B is the highest frequency in
the original signal. If a signal contains a component at
exactly B hertz, then samples spaced at exactly 1/(2B)
seconds do not completely determine the signal,
Shannon's statement notwithstanding.”
http://en.wikipedia.org/wiki/Sampling_theorem

4. What we’re NOT going to talk
about:
 Pulse Code Modulation and uncompressed, digitized
sound
http://en.wikipedia.org/wiki/PCM

5. What we’re NOT going to talk
about:
 How uncompressed, digitized video has to represent
three color values (called red chroma, green chroma,
and blue chroma) and three brightness values (called
red luma, green luma, and blue luma) in zeroes and
ones for each and every pixel, for each and every
frame*
*Other representational schemes (like CCIR-601) condense these values to use fewer
bits-per-pixel, as the human eye sees no real difference when it’s done that way
http://xiph.org/video/vid1.shtml

6. What we’re NOT going to talk
about:
 How “uncompressed digital video” and “uncompressed
digital audio” don’t really exist in today’s world
http://digitalcontentproducer.com/mag/video_uncomp
ressed_digital_video/

7. What we ARE going to talk
about:
 Why your #&*$%*@# video file won’t play in
QuickTime/Windows Media Player/IE/Firefox
 Codecs and Containers
 Web Streaming

8. The Facts:
The word “codec” works like the word “modem”
Code-Decode Modulate-Demodulate
is to as is to
Codec Modem
A codec is a playback algorithm that is specific
to the process used when creating the media
file.

9. The Facts:
 In order to play a video file, your computer must have a
program capable of playing back videos having that
specific file extension, like .MP4, .MOV, .AVI, .FLV,
.VOB, or .ASF – these are known as “container
formats”
 And that program must have access to the codec
specific to videos encoded with that codec in mind

10. The Facts:
 A codec can be part of the computer’s core operating
system, as a codec within its multimedia playback
framework, like in QuickTime or Windows Media Player
 A codec can be part of a self-contained application, like
in VLC Media Player or WinDVD
 A codec can be part of an application’s plug-in
architecture, like the Shockwave Flash plug-in used to
play back Flash videos in Firefox

11. The Facts:
 In the early days of video playback software, only a few
codecs were in use and a codec tended to be exclusive
to a specific media player. This made it easy to
generalize "if the filename has X extension, I'll need
program Y to play it."

12. The Facts:
 Today, you can’t look at the dot-extension on a filename
and know for certain that the program that “goes with”
that container will be able to play back the video
 For instance– ‘Export to QuickTime’ in Avid Media
Composer produces a .MOV file that won’t play back in
QuickTime on a computer that doesn’t have the Avid
codecs installed

13. Answers:
 How can I determine which codecs are installed on my
computer?
Since there are three ways codecs can live on your
computer, it's not so simple to do a “codec check.” If the
video doesn't play at all or plays without sound or with
sound and no picture (and the original tape plays back
fine), you've probably got a codec issue with your media
player.

14. Answers:
 How can I determine which codec was used to encode
a file?
Use VLC Media Player!

15. Using VLC:

16. Using VLC:

17. Adding Codecs to QuickTime:
 Third-party, free codec pack for the Mac– Perian
 Codec pack for Windows Media codecs in QuickTime
as well as the browser– Flip4Mac

18. Adding Codecs to
Windows Media Player:
 Safe, comprehensive, free codec pack for Windows
K-Lite Codec Pack (careful where you get it from)
http://www.majorgeeks.com/K-
Lite_Mega_Codec_Pack_d5230.html
http://codecguide.com/download_k-
lite_codec_pack_mega.htm

19. Codecs in Video Editing
Software:
 In today’s world you’ll commonly convert a video file having one codec
into a different video file having a different codec. Doing this is called
‘transcoding.’
 Depending on which codecs are involved (which determines the
complexity of the job) and the speed of your computer hardware, it may
be possible to transcode media streams in real time, or even faster-than-
realtime.
 When you 'capture’ footage to a modern video editing suite, it’ll usually
automatically transcode into the software's preferred native, internal
codec, or, in Apple terms, an 'intermediate codec.' This is done to optimize
video response of the software's playback window.

20. Web Streaming:
 Guess what? It’s ALL streaming!
 Within the container, audio and video streams can be
‘muxed’ or ‘de-muxed,’ that is, seen as separate
streams by the media player or as a single, integrated
stream (VLC can show you which streams in your
container are muxed and which ones aren’t)
 Each stream is pulled through the player at a different
rate– think of this as the bitrate for playback

21. Web Streaming Protocols:
 When you’re streaming media over a network
connection, the protocol serves as your container
 RTSP– Real Time Streaming Protocol– used by
RealMedia/RealVideo/RealAudio and QuickTime
Streaming
 RTMP– Real Time Messaging Protocol– used for Flash
video/audio only
 MMS– Microsoft Media Services
 HTTP streaming media/HTML5