pulseaudio architecture

Posted on November 7, 2022 by

PulseAudio server may publish its address and credentials via the X11 root window properties. Mutexes are rare, threads use event loops and exchange asynchronous messages. A module can monitor various external events, like a Udev event, a D-Bus signal, or socket I/O. If you want to be able to kill the daemon without it respawning, make these changes:-, Copy the client configuration file to ~/.config/pulse. Every mapping defines a playback or capture ALSA device that is available when this profile is active, and the configuration sets available for each device. It cant guarantee extremely low latency. The intended role list of a device is provided by the device backend. Samples are sent as-is, without any additional encoding. A non-implemented PriorityRouting proposal exists, aimed to make routing more consistent and transparent: Some projects implement their own PulseAudio modules that replace or modify default routing scheme: Tizen IVI (Linux for In-Vehicle Infotainment) project uses Murphy, a resource policy daemon that manages things like audio, video and network connections. The RTP is designed to be an extremely extensible protocol. When a new stream appears, automatically updates its volume based on its name and a preconfigured match table. When access is acquired, the application may use the device until it receives a signal indicating that exclusive access has been revoked. Software mixing of multiple audio streams, bypassing any restrictions the hardware has. For cards with an amplifier, volumes below this point employ hardware amplification, and volumes above this point employ digital (software) amplification. Since sender and receiver clocks are always slightly different, the receiver queue size is slowly drifting. The trick, (for now? Source: pulseaudio Source-Version: 13.0-4 We believe that the bug you reported is fixed in the latest version of pulseaudio, which is due to be installed in the Debian FTP archive. When multiple filter chains are employed, the configuration becomes totally confusing. Since sound cards have their own clocks, an application cant use a CPU timer to send samples to the sound card. For example, its not possible to write a module that improves the RTP support without reimplementing SAP/SDP support or reuse the Zeroconf discovery for an alternative transport. This interface is usually not used directly. Add support for the JACK Audio Connection Kit. Publishing is implemented for both Avahi (module-zeroconf-publish) and Bonjour (module-bonjour-publish). To avoid this, RTP receiver adjusts resampler rate on the fly so that samples are played a bit slower or faster depending on the queue size. Audio is much louder than other apps at the same volume level or is distorted even when relatively quiet Try disabling audio effects on the output devices. The module-device-manager was developed for KDE, which uses it by default and provides a GUI tool for manipulating priority lists. The priority list may contain both devices that are available currently or were available in the past. Devices published in the local network automatically appear as new PulseAudio sinks. Note that more generic properties are preferred over more specific ones. In case you later want to remove this Windows service, run PowerShell as administrator again, and this time run the following command to remove the service: C:\pulse\nssm.exe remove PulseAudio. The remote sink input is connected to a sink. Rewinding works by moving read and write pointers of the ring buffers. apt-get update apt-get install pulseaudio socat apt-get install alsa-utils Im only installing alsa-utils for the wav file, so you could remove this. See Flatpak for more info. Connect a recording application to a source. This check uses a feature of Unix domain sockets that provide a way to securely determine credentials of the other side. Although its possible to implement filters as LADSPA plugins, all filters available out of the box dont use this possibility. dmix and dsnoop are ALSA virtual devices that implement software mixing and support sharing the same device between multiple applications. When a sink reads samples from a sink input, the sink input requests more samples from the application. Pulseaudio becomes the default when the package is installed. PulseAudio supports several filters, like channel remapping and echo cancellation. Packets are usually allocated from a global per-process pool. Each thread installs a thread message queue (pa_thead_mq which uses pa_asyncmsgq) to handle asynchronous messages for message objects (pa_msgobject). This will lock your SBC encoder to work at a bitpool size of 53 - in dual stereo mode. Equal to the difference between the write index and read index. All of the numerous PulseAudio features are implemented in terms of the four objects. In practice, this module is only relevant for ALSA cards. sound servers, like sndio, PulseAudio, JACK (low-latency professional-grade audio editing and mixing) and PipeWire, and higher-level APIs (e.g OpenAL, SDL audio, etc.) a pair of a source output and sink input connected with a queue, connect the loopback source output to the source, set the media.role property of the loopback sink input to music (for A2DP) or phone (for HSP/HFP), which may be used for routing, let PulseAudio route the loopback sink input to some sink, connect the loopback sink input to the sink, set the media.role property of the loopback source output to phone, which may be used for routing, let PulseAudio route the loopback source output to some source, to add software sound processing on top of a real device, when its missed in hardware (e.g. Higher-level frameworks that use PulseAudio (like GStreamer) usually do it automatically. PulseAudio server monitors services published on the local network. The currently active UCM verb, UCM modifier, and UCM devices define what card inputs and outputs are active, what device options are set, and what volume controls are used. Zero or multiple UCM devices may be active at the same time. The equalizer levels can now be controlled with the Qt GUI called qpaeq. Note that PulseAudio server is also able to emulate ESound server. Note that the actual stream latency may be higher than requested by an application. It would be much simpler to understand and improve it if it was a standalone component. One PulseAudio card is created for every discovered Bluetooth device. A source output is a recording stream. These fake clients keep the server opened until the last user session ends. Seamless support for PulseAudio, JACK, ALSA and GStreamer applications. Some applications will handle these events and pause/resume playback. Like PulseAudio, Enlightened Sound Daemon is a sound server accessed by applications via a socket. Rewind request may be issued on a sink input or sink. This means that the user has configured some priority lists to be used for a role or globally. See Bluetooth page for details. At any time, a sink input or source output may be moved to another sink or source. The typical use case for this method is to run PulseAudio applications that dont support ALSA (like Skype) on a system that uses ALSA, without switching the entire system to PulseAudio. On the diagram above, the minimum possible latency is shown as a vertical bar between the two red lines. Typically, every card has at least one playback device and one capture device. If the filter.apply is set and not disabled by the filter.suppress property, and the filter is not loaded yet, the module does the following: Checks if this is a group filter, which uses a paired source and sink and therefore requires a paired source output and sink input. All communications with the server happen inside the main loop. HCTL interface implements a caching layer on top of the CTL interface. Meaning, it acts as a proxy for all the sounds your system produces. Creates RTP source output that sends samples to a preconfigured address, and broadcasts SDP/SAP announcements for it. Connect the loopback sink input to the tunnel sink using the pavucontrol tool. Here is the list of cases when a rewind request is issued on a sink input or sink: The client explicitly overwrites previously written samples by specifying a seek offset. Every routing step is implemented in a separate module. Hyperleap helps uncover and suggest relationships using custom algorithms. Sample - A named batch of samples in the sample cache. Since the server and client use the same shared memory pool, the chunk payload can be obtained from the memory pool using the chunk identifier in the chunk header and is not needed to be transmitted. These properties may be then read by clients running on the same X display, including remote clients that use SSH X forwarding. The reason for an extra thread is that its not possible to add custom event sources to the JACK event loop, hence PulseAudio event loop cant be embedded into it. Useful when filter.want or filter.apply property is set automatically, but application wants to disable it. PulseAudio implements an extensible routing algorithm, which is spread across several modules. This module implements a sink input. pasuspender tool is a wrapper for applications that require an exclusive access to devices. pre { background-color: #DDDDDD; font-size: 1.25em; line-height: 1.5; } The shared memory pools combined with the memory exports and imports are used to implement the zero-copy mode. Run bluetoothctl to pair and connect with the speaker (Note: that pulseaudio . Text client streams, like the CLI and HTTP streams, are based on this channel. A format for describing multimedia session parameters. The job of PulseAudio is to pass sound data between your applications and your hardware, directing sounds coming from ALSA to various output destinations, such as your computer speakers or headphones. When this happens, and several modules need the same mechanism, two scenarios are possible: The implementation of the mechanism may be reimplemented in every module, but a bit differently, fitted for the concrete policy that the module needs. This project is implemented as a standalone daemon written in Python. Similarly, when the user unplugs something from an analog jack, that typically makes some port unavailable and may also make another port available. It may be used to poll the request status, set completion callback, or cancel the request. May be associated with a card and device port. PulseAudio clients can send audio to "sinks" and receive audio from "sources". Besides the three modules described above, the module-default-device-restore saves (on a timer event) and restores (on start) the fallback source and sink. Intercepts XKB bell events and plays a preconfigured sample from the sample cache instead of the default X11 bell. When all such source outputs disappear, switch the card profile to A2DP. The pacmd tool doesnt work over the network or when the server is running in system mode and doesnt support autospawn. All these message types are used by the native protocol. In the system-wide mode, this API is not used. Connect the remote sink input to a sink using the pavucontrol tool on the remote server. Everything will use it. Starts the "simple" protocol server over a Unix domain socket or TCP socket. The server doesnt load the filter, even if its specified in filter.want or filter.apply. Omitted if the variable wasnt set. When the client sends a chunk to the server, the chunk may pass through zero, one, or two sockets buffers: If a TCP socket is used, both client and server have their own kernel-side socket buffers. than to emulate GNU/Linux audio architecture (ALSA) and to use GNU/Linux sound server (PULSE) from the systemd developer, An application may start PulseAudio server as if it were an ESound server, and PulseAudio will notify the application that it was successfully started with a signal of via a file descriptor. The new fallback device will be used only when a new stream is routed. One PulseAudio source and/or one PulseAudio sink is created for every PulseAudio card depending on the currently active card profile. Represents a configuration set for a single capture or playback ALSA device. The best alternative is VB-Audio VoiceMeeter, which is free. However, details vary depending on whether UCM is in use or not. Buffers are rewound to overwrite silence with newly available samples and play them immediately. Creates a filter sink that applies an audio filter from an external LADSPA plugin on top of the master source or sink. The client corks (pauses) or uncorks (resumes) the stream. Please let me know about any issues. If a Unix domain socket is used, the client and server share the same kernel-side socket buffer. It works like a proxy. When a client creates a context or a stream, it may specify its role via the media.role property. PulseAudio is a network-capable sound server program. This provides the ability to use the remote server's speakers for audio output. Each tunnel connects a single pair of a local device and remote stream: Each tunnel acts as a regular PulseAudio client and connects to a remote PulseAudio server via the native protocol over TCP. Hence, in some cases, the user can just connect a device or a stream to a transport, while in other cases the user has to configure tricky adapters like the loopback and null sink. The routing rules are implemented independently in every module, which may lead to inconsistency. I am cross compiling pulseaudio package for arm architechture on linux platform .while cross compiling it is asking for shared libraries such as glib2.0 from other package i want to know that this dependent shared library should also be cross compiled and given to pulse audio . Usually used to stream music. Since the client application, the PulseAudio network thread, the PulseAudio device thread, and the sound card run in parallel and may be clocked independently, there are additional small delays caused by scheduler jitter and non-synchronous timers. Client - An application connected to the PulseAudio server. Every stream is associated with a sink input or source output on the server, which may be connected to a sink or source. When this number becomes higher than the watermark, the watermark is The file can be either loaded immediately or lazily. The priorities of ports and profiles are defined by their backend. The timer-based scheduler may be enabled or disabled globally or per-sink. Every network transport is implemented from scratch. Its up to the implementation how to handle the samples: write them to a sound card, send them over the network, perform sound processing or whatever else. A GUI for routing audio to a remote device available in LAN. Each module monitors both existing and new objects: When an appropriate parameter of an existing object is changed by the user, the module stores the object ID, parameter ID, and parameter value into the database. (Not all modules are shown.). Tell the init script that we really do want to do this, and then start it up: For a more permanent solution, add the following to the default.pa file. Client searches for a cookie in an environment variable, in the X11 root window properties, in parameters provided by the application, and in the cookie file (in this order). Some features rely on the Linux and Unix desktop stack, therefore non-Unix desktop support is even more limited. This led me to dig into PulseAudio internals and eventually to this document. A sink is an output device. As a workaround, PulseAudio can artificially synthesize X11 media key events along with the cork or uncork request, as if the pause or play multimedia keyboard button was pressed. The following list gives an idea of the features implemented in PulseAudio. If the sound is registering in the vu vumetre of that program, then it is being routed through the pulse system. The rewind request may be truncated if some samples were already played and cant be rewound. Publishes server address and credentials via the X11 root window properties, which may be read by clients running on the same X display, including remote clients that use SSH X forwarding. pavucontrol (PulseAudio Volume Control) provides the following features: This tool uses the C API to communicate with the server. An application specifies what sound processing tools it wants for a stream, and the server performs all necessary configuration. Linux platrform cross compiling pulseaudio for arm architecture. These are some of PulseAudio's features: * High quality software mixing of multiple audio streams with support for more . Sample streams are based on the block queues. This problem is addressed by the Roc Toolkit project that Im currently working on. The user just wants to select the source, destination, and transport. The diagram below illustrates relations between PulseAudio and ALSA objects when the UCM is active. On every tick of the sound card timer, an interrupt (a.k.a. The user can enable encodings via pavucontrol GUI. Routing is a process of choosing to which device (source or sink) to connect a new stream (source output or sink input). It contains lists of playback and recording streams. PulseAudio server-side objects may be inspected and controlled via an experimental D-Bus API. Monitors GConf directory and automatically loads PulseAudio modules listed there. The currently active card profile defines what Bluetooth profile and role are used, and so what transport protocols and codecs are used. Module registers I/O or timer event handler in the core event loop, and core invokes handlers when the event is fired. re-sampling 44.1 kHz to 48 kHz is faster than re-sampling either to 192 kHz). Operating Theatre Complexes, Central Sterilising Units, Ward Rooms, Radiology Clinics, Consulting Suites, Reception & BoH facilities, Kitchens & Biomed Facilities. Since version 11.0, PulseAudio has built-in support for RAOP2. PulseAudio automatically creates a source for every detected input device. pause the stream. The parameters of a virtual sink (like equalizer sink) are changed. Additionally, the virtual sink stores a frame of recently written samples. Home; Flounder. An application connects to the server via the native protocol and creates a recording stream. Network transparency: the application can play or record audio on a computer other than the one on which they run. PulseAudio implements a per-device timer-based scheduler that provides clocking in the sound card domain, maintains optimal latency, and reduces the probability of playback glitches. All clients that have access to the current X11 display will be able to connect to PulseAudio server too. Physically it is a [Mapping] section in the profile file. This method is used in the native protocol. In the case of an ALSA sink, this is the kernel-side ALSA ring buffer. The module performs three functions: Maintains a database with multiple priority lists of devices: one priority list per role, and one default priority list. See About and Ports pages on wiki. You will likely have to create that file. If the stream has its own properties, they override the client properties. Physically it is a .conf file under the "/usr/share/pulseaudio/alsa-mixer/profile-sets" directory. The core provides two global registries accessible in modules: The name registry (pa_namereg) is a global hashmap that contains objects of the following types: These objects are always added to the name registry when theyre created, and modules can access them by name. All of these mechanisms are implemented independently and are bound to a concrete type of transport or device. Traditionally, this is achieved by either blocking on ALSA write or read operation until the sound card updates the ring buffer, or waiting for it using poll or select. Its not easy to guess optimal buffer size and period size because they depend on the latency, hardware, CPU, and average system load. This means that every hour the first timer outruns the second by approximately 200 milliseconds. If non of these environment variables are set, the runtime directory is created in "/tmp", and a symlink to it is created in the home directory. The native protocol streams employ this channel to exchange control commands and chunk identifiers in the zero-copy mode, when the client and server are running on the same host and use a shared memory pool. The Team has years of experience in complex, large & fast track projects. With the timer-based scheduling, PulseAudio is able to fulfill the two requirements at the same time: the server usually doesnt introduce glitches by itself even with low latency values, the client doesnt bother about the ring buffer parameters and advanced timing techniques and can just request the latency it needs. Control commands are sent in both directions. The second one (module-device-manager) is used when the user configures preferred devices for a category of streams. The UCM then performs all necessary configuration automatically, hiding machine-specific details and complexity of the Mixer interface. Multimedia buttons available on some keyboards are handled using evdev, a generic input event interface in the Linux kernel, usually used in programs like X server and Wayland. 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pulseaudio architecture