Category Archives: Battling with Tech

How to do things with your gadgets – usually learned the hard way

Video formats

There are more video formats than you can shake a stick at. Those most commonly encountered are introduced below, but even a few minutes study of the web will show that this barely skims the surface.

A video file format has two essential parts (I) the ‘container’ that holds and transports the video file; and (2) the video and audio itself, which is compressed or ‘encoded’ so that it takes up as little space as possible, allowing it to be transported efficiently over the internet, or stored in as little space as practicable on the disk. Note that a ‘codec’ is not the actual video and audio: it is the software or hardware that expands the compressed digital information into the actual pixels that you view.

When you create a video, you use software/hardware to turn the pixels into the encoded form of your choice. When you view a video, you need a decoder that can interpret the encoded data and turn it back into the pixels that you want to view.  Both of these processes are very processor intensive and often use dedicated hardware specially designed to do this.

One of the most common is MPEG4, which uses the file extension .mp4.  It is a ‘container’ format that includes video and audio and allows for streaming over the internet.  It is essentially identical to the Quicktime format published in 2001 and was revised in 2003 (commonly know as MPEG version 2.)  It usually uses a compression format known as H.264.  There are also some sub-sets of the MPEG4 that are used for audio-only files.

AVCHD is a format designed jointly by Sony and Panasonic for HD camcorders recording onto SD card and DVD.  It can be played on HDTVs and it can also be burnt to DVD for replay on Blu-ray Disc players (but not on consumer DVD players).  It uses the H264 video codec and the AC3 [5.1-channel Dolby)] audio codec, which is one difference between AVCHD and MP4.  AVCHD records a higher-quality video image than MP4, because although both use H264, AVCHD uses CABAC encoding, said to be a lossless encoding system.  It is the only option to get the best out of these camcorders. It is regarded as suitable for professional use. (My Panasonic camcorder uses AVCHD and the picture quality never ceases to amaze me.) It needs more powerful encoding and decoding engines and tends to give a larger file size than MP4.  These can lead to more restricted compatibility than MP4.  AVCHD files usually have the extension M2TS, which is also the Blu-ray file extension.  It is similar to the MPEG-2 container.

MPEG2 uses the file extensions .mpg, .mpeg and .m2v.  The video encoding is H.262 and the audio encoding is MP3 and other formats.  It is a fairly lossy compression method but is widely used in over-the-air TV transmission and in DVDs, as it is less demanding in transmission and storage bandwidth.

MPEG1 uses file extensions .mpg, .mpeg, .mpe, .mpv. so these don’t entirely distinguish between MPEG1 and MPEG2,   It is an old standard used to compress VHS-quality raw video and CD audio down to 1.5 Mbit/s (requiring a 26:1 video compression and 6:1 audio compression).  It includes the MP3 audio standard and is very widely used, including in DAB radio broadcasting.

AVI is an old format devised by Microsoft for showing video and audio on computers. It divides the file’s data into chunks, and the data inside any chunk can contain audiovisual data using virtually any compression scheme, but dividing the file in this way creates some additional overhead. Moreover, the ‘chunking’ procedure causes problems with some modern encoding methods.  Its successor is WMV.

WMV or Windows Media Video is an newer format devised by Microsoft that was specifically designed to allow streaming over the internet.  WMV version 9 was also adopted for HD DVD and Blu-ray Disk. There are several different encoding formats necessitated by developments in video display devices.  Whilst the encoding format does not include Digital Rights Management (DRM) anti-piracy features, the ASF container stream can, and this causes many complaints.

MOV is Apple Quicktime Movie format.