VCU Libraries

Research Guides

Convert Video Formats

This guide will help you understand digital video formats and convert them to suit your needs.

Glossary

SOME DIGITAL VIDEO FILE EXTENSIONS

3gp   Global mobile phone video
asf   MS Advanced Streaming Format
avi   Container for Windows Video
divx   Licensed Mpeg-4 video
 dv   Digital video
flv   Flash Video (used by YouTube)
ivr   Internet Video Recording (Real)
m2ts   Blu-Ray Disc Audio/Video (BDAV)
mkv   Open Source Container (Matroska)
 mov   Container for Apple Video
mp4   Container for Mpeg-4 video *
mpg   Mpeg-1 VHS quality video
mpg   Mpeg-2 DVD quality video
mts   HD Advanced Video Codec
rv   Real Video
swf   Shockwave Flash (popular for games) 
VOB   Video Object (DVD Mpeg-2)
vp8   Google Open Codec
 webm   vp8 Container for HTML5
wmv   Windows Media Video
xvid   Open Source Mpeg-4

 

* MPEG-4 is still a developing standard, divided into a number of parts. Companies promoting MPEG-4 do not always clearly state which part they have licensed. The key parts to be aware of are MPEG-4 part 2 (Advanced Simple Profile, used by codecs such as DivX, Xvid and Quicktime 6) and MPEG-4 part 10 (AVC/H.264 or Advanced Video Coding, used by Quicktime 7 and by high-def video media like Blu-ray Discs).

Finding Your Codecs


Locating codecs installed on a PC involves going to Control Panel / Sound and Audio
Devices / Hardware / Video Codecs / Properties / Properties. An easier, and more helpful option is to use a codec utility like  Sherlock Codec Detective, a standalone application for Windows XP to show all installed codecs and which ones are not working properly.

Image of Sherlock Codec Detective
On a Mac, installed codecs will be listed in your format options when you are exporting a movie in Quicktime, iMovie or Final Cut. Also, if you try to play a movie and don't have the codec installed, you will be told to download.

Codecs

Codec stands for Compressor/Decompressor and is an algorithm for defining compression. Codecs compress your video file into a format for you to use on your computer, portable media player, DVD player, etc. Some codecs come with your computer, others need to be installed.

Depending on which codec you use, you may end up with a proprietary file extension like .flv or .wmv (see glossary to left). 

Some codecs bury themselves within a wrapper, or container, like .avi or .mov.  A container is a type of file format enclosing various types of data compressed by codecs. These formats are essentially wrappers in that they don't specify what codec is being used, but rather it defines how the video, audio and other data is stored within the container.

If you have a video file and don't know which codec was used, there is software available to help you identify them, such as GSpot (see screenshot below) for Windows, or VideoSpec for a Mac.  


GSpot

A Little on Streaming

Image of Streaming MediaStreaming Media is the sending of a media file over the Internet as a series of small data packets to be viewed in a real time fashion through the use of a Media Player.  Unlike downloading (or Podcasting), no files remain on the harddrive once the viewing is complete.  Streamed media may originate from a file OR from a live feed camera running through a streaming server. Additionally, streamed media may be assigned multiple bitrates, meaning within the file is encoded the necessary data to stream accordingly to a low bandwidth connection (like dial-up modems) or to a fast connection (like T1).

Often mistaken for streaming, progressive downloading is when a media file on a remote web server is played from the server. This creates a temporary file on your machine. Depending on your connection speed, it can often take extra time for the video playback to catch up to the downloaded information in the temp file, which is called buffering.