Audio files

Sound files are divided into two large groups - uncompressed and compressed (the latter group is also subdivided into compressed with loss of quality and lossless). Files, which are compressed with loss of quality, are better suited for use in the training materials, as they provide the smallest file size, and loss of quality does not matter. Recommended compression parameters: bitrate 128 kbps or less, sampling frequency 44100 Hz or less (for voice files 22050 Hz is usually enough). Also please note that some mobile devices cannot play audio files with bitrate more than 160 kbps.

Very important parameter of audio file is browser support. Modern browsers have built-in mechanisms of playback of some common files - without any plugins. Other formats may require additional browser plugins (Windows Media Player, QuickTime Player, Flash Player etc.).

MP3

This is probably the most common format of audio with compression (.mp3). It is supported internally by almost all modern browsers (but not all). Lack of browser support is due to patent issues (the latest patent on MP3 format will expire in 2017). Nevertheless, we recommend to use this format of audio (probably in bundle with OGG).

OGG

Quite common format of audio with compression (.ogg, .oga). Ogg is open source standard that have no patent or license restrictions. It is supported internally by almost all modern browsers (but with the exception of Internet Explorer family). It is recommended to use this format as bundle to MP3.

WAV

Format without compression (.wav). Such files have quite large size, but is still quite common, because some audio recording software save files in this format. It is supported internally by almost all modern browsers (but with the exception of Internet Explorer, which requires Windows Media Player plugin to play such files). We recommend to convert such files to MP3/OGG format.

SWF

Flash-movies with embedded audio (.swf). All browsers require Flash Player to play such files. While Flash Player is very common browser plugin, some mobile devices do not support Flash Player, therefore it is not recommended to use such files in courses.

WARNING! Starting from year 2020 browsers will stop Flash support.

Bundle files

CourseLab runtime uses "bundle" technology to play MP3 files:

• runtime sends request to play MP3 to the browser,
• if the browser confirms that it can play this file, then runtime starts playback of the file,
• if the browser denies playing such file, then runtime sends request to play OGG to the browser,
• if the browser confirms that it can play OGG file, then runtime attempts to start playback of the file with the same name, but with .ogg extension.

Usually the browsers that do not support MP3 - supports OGG (and vice versa), therefore such MP3/OGG bundle allows to play sound in almost any case. To make such bundle please prepare 2 audio files: MP3 and OGG with the same name, but different extension (.mp3 and .ogg), select MP3 file as the main audio file (via Format dialog or Object's parameter), then add the file with .ogg extension into the Module using special Additional files Object.

About MIME-types

Some browsers require that web-server must provide correct type of file in response header (so called MIME Type) an dp not start playback of file if the MIME type does not correspond to expected type. Some outdated LMS servers provide incorrect MIME types for modern media files. Therefore some "browser-server" combinations may lead to failure to play the file. This is not the course error - in this case you may need to configure web-server to provide correct MIME type.