When looking into how video conversions are done its often worth understanding how media files are structured.
All media files (video and audio) start with what is called a container. A container is sometimes called a 'wrapper' which is a good way of thinking of a container.
The container defines details of the file, including:
- the media streams it contains - a file can include one or many streams. For example, some movie files include a video stream and multiple audio streams, covering many languages;
- other files, such as subtitles;
- file length and duration; and
- other details which vary from container to container.
Container formats also coincide with file extensions that you can see on the files. File extensions are used by the operating system to decide which application to open when the file is double-clicked.
The Shedworx conversion engine takes no notice of the file extension when it converts the file. Instead, it looks into the file itself to see what container format it is.
Common container formats (and therefore file types) that you have probably seen include:
- MP3 (MPEG 3) - Motion Picture Expert Group version 3, which is a container format usually used for audio;
- MP4 (MPEG 4) - Motion Picture Expert Group version 4, which is a very common ISO standard used for movies;
- MOV (Quicktime) - Apple's Quicktime proprietary multimedia container; and
- MKV (Matroska Multimedia Container) - an open source container format that is free to use by any application with no licencing cost. Note that MKV files can't be played directly on a Mac or Apple TV.
There are many more container formats out there, but these are the main ones you're likely to come across.
Movie files contain at least one video stream. Most movie files contain just the one stream, but can contain multiple video streams. When this happens it is usually to provide a number of different resolutions of the video stream.
Just like containers, there are many video stream formats out there. The two most common formats are:
- H.264 - a very common video format that can be found in MP4, MOV and MOV containers;
- H.265 - a newer version of H.264, more suited to streaming video, with better compression than H.264. Also known as High Efficiency Video Coding (HEVC).
While there are only a couple of common video stream formats, there are quite a few common audio formats. This is mainly to do with surround sound, which tends to include a number of formats owned by Dolby corporation.
Common audio formats include:
- MPEG-2 - this is the audio format that can be found inside an MP3 container; and
- AAC (Advanced Audio Coding) - a successor to MPEG-2 audio common used in movie files today.
That's a quick overview of media files, container and streams. We hope this sheds some light on the world of video management and conversion which helps you manage you media libraries.
You can find a wealth of knowledge about all the terms mentioned in this article on Wikipedia if you're interested in learning more.