Sep 15, 2009 — Advanced Linux Sound. Architecture (ALSA). ALSA kernel drivers. Kernel low latency requirements. ALSA userspace interface. Sound servers
97 pages
89 KB – 97 Pages
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2Free Electrons . Kernel, drivers and embedded Linux development, consulting, training and support. http//free-electrons.com Rights to copy Attribution ± ShareAlike 3.0 You are free to copy, distribute, display, and perform the work to make derivative works to make commercial use of the work Under the following conditions Attribution . You must give the original author credit. Share Alike . If you alter, transform, or build upon this work, you may distribute the resulting work only under a license identical to this one. For any reuse or distribution, you must make clear to others the license terms of this work. Any of these conditions can be waived if you get permission from the copyright holder. Your fair use and other rights are in no way affected by the above. License text: http://creativecommons.org/licenses/by-sa/3.0/legalcode Copyright 2004-2009, Free Electrons feedback@free-electrons.com Document sources, updates and translations: http://free-electrons.com/docs/audio Corrections, suggestions, contributions and translations are welcome! Latest update: Sep 15, 2009
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3Free Electrons . Kernel, drivers and embedded Linux development, consulting, training and support. http//free-electrons.com Scope of this training Audio in embedded Linux systems This training targets the development of audio-capable embedded Linux systems. Though it can be useful to playing or creating sound on GNU/Linux desktops, it is not meant to cover everything about audio on GNU/Linux. Linux 2.6 This training only targets new systems based on the Linux 2.6 kernel. This way, you leverage the most advanced technology and don©t learn about something getting obsolete.
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4Free Electrons . Kernel, drivers and embedded Linux development, consulting, training and support. http//free-electrons.com Contents (1) Introduction Glossary Audio codecs and file formats System perspective System overview Advanced Linux Sound Architecture (ALSA) ALSA kernel drivers Kernel low latency requirements ALSA userspace interface Sound servers
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5Free Electrons . Kernel, drivers and embedded Linux development, consulting, training and support. http//free-electrons.com Contents (2) Free Software audio Audio players for the embedded target Audio encoders Creating your own applications Miscellaneous Speech synthesis Audio distributions References
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6Free Electrons . Kernel, drivers and embedded Linux development, consulting, training and support. http//free-electrons.com Quick Glossary PCM : Pulse Code Modulation Digital audio encoding, representing the amplitude of a signal at uniform intervals. Codec : coder / dec oder Program or device coding and / or decoding a data stream or a signal. MIDI : Musical Instrument Digital Interface. Standard to control electronic musical instruments. See http://wikipedia.org for details!
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8Free Electrons . Kernel, drivers and embedded Linux development, consulting, training and support. http//free-electrons.com MP3MPEG-1 Audio Layer III from the Fraunhofer Society Lossy audio format Bitrates from 32 to 320 kbit/s Quality depends on the bitrate: 128-192: good, 192-224: very good, 224-320: excellent Depends also pretty much on the encoder and on the source. Depends on the listener too! The most popular. Users have lots of files in this format. Free Software encoders and decoders exist But relies on patented algorithms. Depending on which country you sell to, you may have to pay for a license. Licenses can apply to encoding, decoding or even songs! Ask for legal advice! See http://en.wikipedia.org/wiki/Mp3 for details
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9Free Electrons . Kernel, drivers and embedded Linux development, consulting, training and support. http//free-electrons.com AACUsed on some on-line music stores (Apple iTunes) and portable players (Apple iPod). Also burdened by patents, like MP3. License needed to encode and read this format. Free Software decoders available. Just one Free Software encoder available (faac). More details on http://en.wikipedia.org/wiki/Advanced_Audio_Coding Advanced Audio Coding MPEG-4 Audio Standard format from the MPEG group: Dolby, Fraunhofer, AT&T, Sony, and Nokia Lossy audio format Designed to replace MP3. Consistently better audio quality than MP3 at lower bitrates. Can be DRM encrypted (FairPlay).
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10Free Electrons . Kernel, drivers and embedded Linux development, consulting, training and support. http//free-electrons.com RealAudio From RealNetworks http://realnetworks.com/ Lossy audio format Proprietary format Designed for very low bandwidth connections. Bitrates: 12 to 800 kbit/s Now uses AAC at 128 kbit/s and more. Lossless format also supported Free Software decoder available: mplayer Mainly used for streaming, used by a significant number of on-line media. Useful for mobile devices connecting to these media. Only proprietary encoders. RealNetworks encoder free of charge only for personal use. More details on http://en.wikipedia.org/wiki/Real_Audio
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11Free Electrons . Kernel, drivers and embedded Linux development, consulting, training and support. http//free-electrons.com WMAWindows Media Audio Microsoft proprietary, as a alternative to MP3 (patented by somebody else) and now AAC. Almost always encapsulated in an Advanced Systems Format (ASF) file. File extensions: asf or wma Supports constant and variable bitrates, and lossless compression. Can be DRM encrypted. Now supported by more and more digital players and on-line music stores. Users may ask for WMA playing capability. Lack of Free Software players (except libavcodec ) and encoders. Relies on patented algorithms. Licenses may apply to encoding, decoding or even songs, though MS is still very tolerant so far (to achieve dominance). See http://en.wikipedia.org/wiki/WMA for details
89 KB – 97 Pages