Codecs

This article is meant as a brief explanation of the most common codecs used on BakaBT and is purely information. For codec troubleshooting, see the Common Playback Problems BakaBT Wiki article, or visit the Playback Forum for help playing/installing codecs.

Overview

A codec is a device or software that is capable of decoding and/or encoding data, wether it be a digital data stream or signal. Basically, they are what we use to encode and decode virtually all of the content found on BakaBT. For the most part, we only worry about the decoding.

Compression

Basically, two types of compression exist, Lossy, and Lossles. For example, most of the anime found on BakaBT will use Lossy codecs, where as several soundtracks use Lossless.

• Lossy codecs - Many of the more popular codecs in the software world are lossy, meaning that they reduce quality by some amount in order to achieve compression. Smaller data sets ease the strain on relatively expensive storage sub-systems such as non-volatile memory and hard disk, as well as write-once-read-many formats such as CD-ROM, DVD and Blu-ray Disc.
• Lossless codecs - There are also many lossless codecs which are typically used for archiving data in a compressed form while retaining all of the information present in the original stream. If preserving the original quality of the stream is more important than eliminating the correspondingly larger data sizes, lossless codecs are preferred. Especially if the data is to undergo further processing (for example editing) in which case the repeated application of processing (encoding and decoding) on lossy codecs will degrade the quality of the resulting data such that it is readily identifiable (visually, audibly or both). Using more than one codec or encoding scheme successively can also degrade quality significantly. The decreasing cost of storage capacity and network bandwidth has a tendency to reduce the need for lossy codecs for some media.

Video Codecs

Currently, many formats exist for video codecs, here are the more common ones found on BakaBT:

• MPEG-2 - the codec which is used on DVDs and on some Blu-ray/HD-DVD discs.
• MPEG-4 Part 2 - also known as MPEG-4 SP/MPEG-4 ASP. Popular software implemantations are: DivX, Xvid, 3ivx
• MPEG-4 Part 10 - also known as MPEG-4 AVC/H.264. Used on Blu-ray/HD-DVD discs.
• WMV - codec developed by Microsoft.
• VC-1 - H.264 rival. Used on Blu-ray/HD-DVD discs. Can be offloaded via DXVA on recent ATI GPUs and the newest nVidia GPUs.
• x264 - Open Source (free) implementation of H.264 standard. Can be offloaded via DXVA on nVidia and ATI GPUs.

Audio Codecs

Several audio formats exist as well, these apply to both movies and music/sounds. Here are some of the common ones used on BakaBT.

• MP3: Lossy codec that is commonly supported by just about every media player out there. Can be easily copied over to the portable media player of your choice. Quality is highly dependent on bitrate.

• FLAC: Lossless codec. Offers potentially higher audio quality than MP3, at the cost of higher file size. Is not commonly supported by standard media players or portable media players. Common media players such as Windows Media Player can be made compatible using a plug-in, while other media players such as Media Player Classic Home Cinema have built-in support.

• AAC: Lossy codec. Advanced Audio Coding (AAC) is currently the standard audio codec for TV & DVD in fansubbing and in some cases for Blu-Ray because AAC is capable of producing a better audio quality than MP3 while having the same bitrate.

Text Codecs

Text codecs are used for files that contain softsubs, they are basically text that is rendered during playback separately from the video track instead of being rendered directly to the video file during encoding (hardsubs). The main advantage of using softsubs being that multiple subtitle/karaoke tracks can be packaged into one file or not used at all during playback. The main drawback is that it adds more overhead to the file.

The softsub file is sometimes a separate file, .sub for example, but is usually inside the container file. Here are the most common codecs used on BakaBT:

• SubStation Alpha - Commonly used on BakaBT. Supports both styled text and metadata. Has a precision of 10 milliseconds. Frequently encoded within a container, thus rarely seen as a separate file. Uses a .ssa or .ass extension.
• VobSub - Common on BakaBT as well. VobSub is image-based so it doesn't support styled text or metadata. This is the codec used when the subtitles are ripped directly from the source DVD. These have a precision of 1 millisecond.

• Hardsubs are rendered directly into the video stream so a separate codec isn't required

References

• Video codec from Wikipedia
• Audio codecs from Wikipedia
• Subtitle (captioning) from Wikipedia