LUA SCRIPTING ============= mpv can load Lua scripts. Scripts passed to the ``--script`` option, or found in the ``scripts`` subdirectory of the mpv configuration directory (usually ``~/.config/mpv/scripts/``) will be loaded on program start. mpv also appends the ``scripts`` subdirectory to the end of Lua's path so you can import scripts from there too. Since it's added to the end, don't name scripts you want to import the same as Lua libraries because they will be overshadowed by them. mpv provides the built-in module ``mp``, which contains functions to send commands to the mpv core and to retrieve information about playback state, user settings, file information, and so on. These scripts can be used to control mpv in a similar way to slave mode. Technically, the Lua code uses the client API internally. Example ------- A script which leaves fullscreen mode when the player is paused: :: function on_pause_change(name, value) if value == true then mp.set_property("fullscreen", "no") end end mp.observe_property("pause", "bool", on_pause_change) Details on the script initialization and lifecycle -------------------------------------------------- Your script will be loaded by the player at program start from the ``scripts`` configuration subdirectory, or from a path specified with the ``--script`` option. Some scripts are loaded internally (like ``--osc``). Each script runs in its own thread. Your script is first run "as is", and once that is done, the event loop is entered. This event loop will dispatch events received by mpv and call your own event handlers which you have registered with ``mp.register_event``, or timers added with ``mp.add_timeout`` or similar. When the player quits, all scripts will be asked to terminate. This happens via a ``shutdown`` event, which by default will make the event loop return. If your script got into an endless loop, mpv will probably behave fine during playback, but it won't terminate when quitting, because it's waiting on your script. Internally, the C code will call the Lua function ``mp_event_loop`` after loading a Lua script. This function is normally defined by the default prelude loaded before your script (see ``player/lua/defaults.lua`` in the mpv sources). The event loop will wait for events and dispatch events registered with ``mp.register_event``. It will also handle timers added with ``mp.add_timeout`` and similar (by waiting with a timeout). Since mpv 0.6.0, the player will wait until the script is fully loaded before continuing normal operation. The player considers a script as fully loaded as soon as it starts waiting for mpv events (or it exits). In practice this means the player will more or less hang until the script returns from the main chunk (and ``mp_event_loop`` is called), or the script calls ``mp_event_loop`` or ``mp.dispatch_events`` directly. This is done to make it possible for a script to fully setup event handlers etc. before playback actually starts. In older mpv versions, this happened asynchronously. mp functions ------------ The ``mp`` module is preloaded, although it can be loaded manually with ``require 'mp'``. It provides the core client API. ``mp.command(string)`` Run the given command. This is similar to the commands used in input.conf. See `List of Input Commands`_. By default, this will show something on the OSD (depending on the command), as if it was used in ``input.conf``. See `Input Command Prefixes`_ how to influence OSD usage per command. Returns ``true`` on success, or ``nil, error`` on error. ``mp.commandv(arg1, arg2, ...)`` Similar to ``mp.command``, but pass each command argument as separate parameter. This has the advantage that you don't have to care about quoting and escaping in some cases. Example: :: mp.command("loadfile " .. filename .. " append") mp.commandv("loadfile", filename, "append") These two commands are equivalent, except that the first version breaks if the filename contains spaces or certain special characters. Note that properties are *not* expanded. You can use either ``mp.command``, the ``expand-properties`` prefix, or the ``mp.get_property`` family of functions. Unlike ``mp.command``, this will not use OSD by default either (except for some OSD-specific commands). ``mp.command_native(table [,def])`` Similar to ``mp.commandv``, but pass the argument list as table. This has the advantage that in at least some cases, arguments can be passed as native types. Returns a result table on success (usually empty), or ``def, error`` on error. ``def`` is the second parameter provided to the function, and is nil if it's missing. ``mp.get_property(name [,def])`` Return the value of the given property as string. These are the same properties as used in input.conf. See `Properties`_ for a list of properties. The returned string is formatted similar to ``${=name}`` (see `Property Expansion`_). Returns the string on success, or ``def, error`` on error. ``def`` is the second parameter provided to the function, and is nil if it's missing. ``mp.get_property_osd(name [,def])`` Similar to ``mp.get_property``, but return the property value formatted for OSD. This is the same string as printed with ``${name}`` when used in input.conf. Returns the string on success, or ``def, error`` on error. ``def`` is the second parameter provided to the function, and is an empty string if it's missing. Unlike ``get_property()``, assigning the return value to a variable will always result in a string. ``mp.get_property_bool(name [,def])`` Similar to ``mp.get_property``, but return the property value as Boolean. Returns a Boolean on success, or ``def, error`` on error. ``mp.get_property_number(name [,def])`` Similar to ``mp.get_property``, but return the property value as number. Note that while Lua does not distinguish between integers and floats, mpv internals do. This function simply request a double float from mpv, and mpv will usually convert integer property values to float. Returns a number on success, or ``def, error`` on error. ``mp.get_property_native(name [,def])`` Similar to ``mp.get_property``, but return the property value using the best Lua type for the property. Most time, this will return a string, Boolean, or number. Some properties (for example ``chapter-list``) are returned as tables. Returns a value on success, or ``def, error`` on error. Note that ``nil`` might be a possible, valid value too in some corner cases. ``mp.set_property(name, value)`` Set the given property to the given string value. See ``mp.get_property`` and `Properties`_ for more information about properties. Returns true on success, or ``nil, error`` on error. ``mp.set_property_bool(name, value)`` Similar to ``mp.set_property``, but set the given property to the given Boolean value. ``mp.set_property_number(name, value)`` Similar to ``mp.set_property``, but set the given property to the given numeric value. Note that while Lua does not distinguish between integers and floats, mpv internals do. This function will test whether the number can be represented as integer, and if so, it will pass an integer value to mpv, otherwise a double float. ``mp.set_property_native(name, value)`` Similar to ``mp.set_property``, but set the given property using its native type. Since there are several data types which cannot represented natively in Lua, this might not always work as expected. For example, while the Lua wrapper can do some guesswork to decide whether a Lua table is an array or a map, this would fail with empty tables. Also, there are not many properties for which it makes sense to use this, instead of ``set_property``, ``set_property_bool``, ``set_property_number``. For these reasons, this function should probably be avoided for now, except for properties that use tables natively. ``mp.get_time()`` Return the current mpv internal time in seconds as a number. This is basically the system time, with an arbitrary offset. ``mp.add_key_binding(key, name|fn [,fn [,flags]])`` Register callback to be run on a key binding. The binding will be mapped to the given ``key``, which is a string describing the physical key. This uses the same key names as in input.conf, and also allows combinations (e.g. ``ctrl+a``). If the key is empty or ``nil``, no physical key is registered, but the user still can create own bindings (see below). After calling this function, key presses will cause the function ``fn`` to be called (unless the user remapped the key with another binding). The ``name`` argument should be a short symbolic string. It allows the user to remap the key binding via input.conf using the ``script-message`` command, and the name of the key binding (see below for an example). The name should be unique across other bindings in the same script - if not, the previous binding with the same name will be overwritten. You can omit the name, in which case a random name is generated internally. The last argument is used for optional flags. This is a table, which can have the following entries: ``repeatable`` If set to ``true``, enables key repeat for this specific binding. ``complex`` If set to ``true``, then ``fn`` is called on both key up and down events (as well as key repeat, if enabled), with the first argument being a table. This table has an ``event`` entry, which is set to one of the strings ``down``, ``repeat``, ``up`` or ``press`` (the latter if key up/down can't be tracked). It further has an ``is_mouse`` entry, which tells whether the event was caused by a mouse button. Internally, key bindings are dispatched via the ``script-message-to`` or ``script-binding`` input commands and ``mp.register_script_message``. Trying to map multiple commands to a key will essentially prefer a random binding, while the other bindings are not called. It is guaranteed that user defined bindings in the central input.conf are preferred over bindings added with this function (but see ``mp.add_forced_key_binding``). Example: :: function something_handler() print("the key was pressed") end mp.add_key_binding("x", "something", something_handler) This will print the message ``the key was pressed`` when ``x`` was pressed. The user can remap these key bindings. Then the user has to put the following into his input.conf to remap the command to the ``y`` key: :: y script-binding something This will print the message when the key ``y`` is pressed. (``x`` will still work, unless the user remaps it.) You can also explicitly send a message to a named script only. Assume the above script was using the filename ``fooscript.lua``: :: y script-binding fooscript/something ``mp.add_forced_key_binding(...)`` This works almost the same as ``mp.add_key_binding``, but registers the key binding in a way that will overwrite the user's custom bindings in his input.conf. (``mp.add_key_binding`` overwrites default key bindings only, but not those by the user's input.conf.) ``mp.remove_key_binding(name)`` Remove a key binding added with ``mp.add_key_binding`` or ``mp.add_forced_key_binding``. Use the same name as you used when adding the bindings. It's not possible to remove bindings for which you omitted the name. ``mp.register_event(name, fn)`` Call a specific function when an event happens. The event name is a string, and the function fn is a Lua function value. Some events have associated data. This is put into a Lua table and passed as argument to fn. The Lua table by default contains a ``name`` field, which is a string containing the event name. If the event has an error associated, the ``error`` field is set to a string describing the error, on success it's not set. If multiple functions are registered for the same event, they are run in registration order, which the first registered function running before all the other ones. Returns true if such an event exists, false otherwise. See `Events`_ and `List of events`_ for details. ``mp.unregister_event(fn)`` Undo ``mp.register_event(..., fn)``. This removes all event handlers that are equal to the ``fn`` parameter. This uses normal Lua ``==`` comparison, so be careful when dealing with closures. ``mp.observe_property(name, type, fn)`` Watch a property for changes. If the property ``name`` is changed, then the function ``fn(name)`` will be called. ``type`` can be ``nil``, or be set to one of ``none``, ``native``, ``bool``, ``string``, or ``number``. ``none`` is the same as ``nil``. For all other values, the new value of the property will be passed as second argument to ``fn``, using ``mp.get_property_`` to retrieve it. This means if ``type`` is for example ``string``, ``fn`` is roughly called as in ``fn(name, mp.get_property_string(name))``. If possible, change events are coalesced. If a property is changed a bunch of times in a row, only the last change triggers the change function. (The exact behavior depends on timing and other things.) In some cases the function is not called even if the property changes. Whether this can happen depends on the property. If the ``type`` is ``none`` or ``nil``, sporadic property change events are possible. This means the change function ``fn`` can be called even if the property doesn't actually change. ``mp.unobserve_property(fn)`` Undo ``mp.observe_property(..., fn)``. This removes all property handlers that are equal to the ``fn`` parameter. This uses normal Lua ``==`` comparison, so be careful when dealing with closures. ``mp.add_timeout(seconds, fn)`` Call the given function fn when the given number of seconds has elapsed. Note that the number of seconds can be fractional. For now, the timer's resolution may be as low as 50 ms, although this will be improved in the future. This is a one-shot timer: it will be removed when it's fired. Returns a timer object. See ``mp.add_periodic_timer`` for details. ``mp.add_periodic_timer(seconds, fn)`` Call the given function periodically. This is like ``mp.add_timeout``, but the timer is re-added after the function fn is run. Returns a timer object. The timer object provides the following methods: ``stop()`` Disable the timer. Does nothing if the timer is already disabled. This will remember the current elapsed time when stopping, so that ``resume()`` essentially unpauses the timer. ``kill()`` Disable the timer. Resets the elapsed time. ``resume()`` will restart the timer. ``resume()`` Restart the timer. If the timer was disabled with ``stop()``, this will resume at the time it was stopped. If the timer was disabled with ``kill()``, or if it's a previously fired one-shot timer (added with ``add_timeout()``), this starts the timer from the beginning, using the initially configured timeout. ``is_enabled()`` Whether the timer is currently enabled or was previously disabled (e.g. by ``stop()`` or ``kill()``). ``timeout`` (RW) This field contains the current timeout period. This value is not updated as time progresses. It's only used to calculate when the timer should fire next when the timer expires. If you write this, you can call ``t:kill() ; t:resume()`` to reset the current timeout to the new one. (``t:stop()`` won't use the new timeout.) ``oneshot`` (RW) Whether the timer is periodic (``false``) or fires just once (``true``). This value is used when the timer expires (but before the timer callback function fn is run). Note that these are method, and you have to call them using ``:`` instead of ``.`` (Refer to http://www.lua.org/manual/5.2/manual.html#3.4.9 .) Example: :: seconds = 0 timer = mp.add_periodic_timer(1, function() print("called every second") # stop it after 10 seconds seconds = seconds + 1 if seconds >= 10 then timer:kill() end end) ``mp.get_opt(key)`` Return a setting from the ``--script-opts`` option. It's up to the user and the script how this mechanism is used. Currently, all scripts can access this equally, so you should be careful about collisions. ``mp.get_script_name()`` Return the name of the current script. The name is usually made of the filename of the script, with directory and file extension removed. If there are several scripts which would have the same name, it's made unique by appending a number. .. admonition:: Example The script ``/path/to/fooscript.lua`` becomes ``fooscript``. ``mp.osd_message(text [,duration])`` Show an OSD message on the screen. ``duration`` is in seconds, and is optional (uses ``--osd-duration`` by default). Advanced mp functions --------------------- These also live in the ``mp`` module, but are documented separately as they are useful only in special situations. ``mp.suspend()`` This function has been deprecated in mpv 0.21.0 and does nothing starting with mpv 0.23.0 (no replacement). ``mp.resume()`` This function has been deprecated in mpv 0.21.0 and does nothing starting with mpv 0.23.0 (no replacement). ``mp.resume_all()`` This function has been deprecated in mpv 0.21.0 and does nothing starting with mpv 0.23.0 (no replacement). ``mp.get_wakeup_pipe()`` Calls ``mpv_get_wakeup_pipe()`` and returns the read end of the wakeup pipe. (See ``client.h`` for details.) ``mp.get_next_timeout()`` Return the relative time in seconds when the next timer (``mp.add_timeout`` and similar) expires. If there is no timer, return ``nil``. ``mp.dispatch_events([allow_wait])`` This can be used to run custom event loops. If you want to have direct control what the Lua script does (instead of being called by the default event loop), you can set the global variable ``mp_event_loop`` to your own function running the event loop. From your event loop, you should call ``mp.dispatch_events()`` to dequeue and dispatch mpv events. If the ``allow_wait`` parameter is set to ``true``, the function will block until the next event is received or the next timer expires. Otherwise (and this is the default behavior), it returns as soon as the event loop is emptied. It's strongly recommended to use ``mp.get_next_timeout()`` and ``mp.get_wakeup_pipe()`` if you're interested in properly working notification of new events and working timers. ``mp.register_idle(fn)`` Register an event loop idle handler. Idle handlers are called before the script goes to sleep after handling all new events. This can be used for example to delay processing of property change events: if you're observing multiple properties at once, you might not want to act on each property change, but only when all change notifications have been received. ``mp.unregister_idle(fn)`` Undo ``mp.register_idle(fn)``. This removes all idle handlers that are equal to the ``fn`` parameter. This uses normal Lua ``==`` comparison, so be careful when dealing with closures. ``mp.enable_messages(level)`` Set the minimum log level of which mpv message output to receive. These messages are normally printed to the terminal. By calling this function, you can set the minimum log level of messages which should be received with the ``log-message`` event. See the description of this event for details. The level is a string, see ``msg.log`` for allowed log levels. ``mp.register_script_message(name, fn)`` This is a helper to dispatch ``script-message`` or ``script-message-to`` invocations to Lua functions. ``fn`` is called if ``script-message`` or ``script-message-to`` (with this script as destination) is run with ``name`` as first parameter. The other parameters are passed to ``fn``. If a message with the given name is already registered, it's overwritten. Used by ``mp.add_key_binding``, so be careful about name collisions. ``mp.unregister_script_message(name)`` Undo a previous registration with ``mp.register_script_message``. Does nothing if the ``name`` wasn't registered. mp.msg functions ---------------- This module allows outputting messages to the terminal, and can be loaded with ``require 'mp.msg'``. ``msg.log(level, ...)`` The level parameter is the message priority. It's a string and one of ``fatal``, ``error``, ``warn``, ``info``, ``v``, ``debug``. The user's settings will determine which of these messages will be visible. Normally, all messages are visible, except ``v`` and ``debug``. The parameters after that are all converted to strings. Spaces are inserted to separate multiple parameters. You don't need to add newlines. ``msg.fatal(...)``, ``msg.error(...)``, ``msg.warn(...)``, ``msg.info(...)``, ``msg.verbose(...)``, ``msg.debug(...)`` All of these are shortcuts and equivalent to the corresponding ``msg.log(level, ...)`` call. mp.options functions -------------------- mpv comes with a built-in module to manage options from config-files and the command-line. All you have to do is to supply a table with default options to the read_options function. The function will overwrite the default values with values found in the config-file and the command-line (in that order). ``options.read_options(table [, identifier])`` A ``table`` with key-value pairs. The type of the default values is important for converting the values read from the config file or command-line back. Do not use ``nil`` as a default value! The ``identifier`` is used to identify the config-file and the command-line options. These needs to unique to avoid collisions with other scripts. Defaults to ``mp.get_script_name()``. Example implementation:: require 'mp.options' local options = { optionA = "defaultvalueA", optionB = -0.5, optionC = true, } read_options(options, "myscript") print(options.optionA) The config file will be stored in ``lua-settings/identifier.conf`` in mpv's user folder. Comment lines can be started with # and stray spaces are not removed. Boolean values will be represented with yes/no. Example config:: # comment optionA=Hello World optionB=9999 optionC=no Command-line options are read from the ``--script-opts`` parameter. To avoid collisions, all keys have to be prefixed with ``identifier-``. Example command-line:: --script-opts=myscript-optionA=TEST,myscript-optionB=0,myscript-optionC=yes mp.utils functions ------------------ This built-in module provides generic helper functions for Lua, and have strictly speaking nothing to do with mpv or video/audio playback. They are provided for convenience. Most compensate for Lua's scarce standard library. Be warned that any of these functions might disappear any time. They are not strictly part of the guaranteed API. ``utils.getcwd()`` Returns the directory that mpv was launched from. On error, ``nil, error`` is returned. ``utils.readdir(path [, filter])`` Enumerate all entries at the given path on the filesystem, and return them as array. Each entry is a directory entry (without the path). The list is unsorted (in whatever order the operating system returns it). If the ``filter`` argument is given, it must be one of the following strings: ``files`` List regular files only. This excludes directories, special files (like UNIX device files or FIFOs), and dead symlinks. It includes UNIX symlinks to regular files. ``dirs`` List directories only, or symlinks to directories. ``.`` and ``..`` are not included. ``normal`` Include the results of both ``files`` and ``dirs``. (This is the default.) ``all`` List all entries, even device files, dead symlinks, FIFOs, and the ``.`` and ``..`` entries. On error, ``nil, error`` is returned. ``utils.split_path(path)`` Split a path into directory component and filename component, and return them. The first return value is always the directory. The second return value is the trailing part of the path, the directory entry. ``utils.join_path(p1, p2)`` Return the concatenation of the 2 paths. Tries to be clever. For example, if ```p2`` is an absolute path, p2 is returned without change. ``utils.subprocess(t)`` Runs an external process and waits until it exits. Returns process status and the captured output. The parameter ``t`` is a table. The function reads the following entries: ``args`` Array of strings. The first array entry is the executable. This can be either an absolute path, or a filename with no path components, in which case the ``PATH`` environment variable is used to resolve the executable. The other array elements are passed as command line arguments. ``cancellable`` Optional. If set to ``true`` (default), then if the user stops playback or goes to the next file while the process is running, the process will be killed. ``max_size`` Optional. The maximum size in bytes of the data that can be captured from stdout. (Default: 16 MB.) The function returns a table as result with the following entries: ``status`` The raw exit status of the process. It will be negative on error. ``stdout`` Captured output stream as string, limited to ``max_size``. ``error`` ``nil`` on success. The string ``killed`` if the process was terminated in an unusual way. The string ``init`` if the process could not be started. On Windows, ``killed`` is only returned when the process has been killed by mpv as a result of ``cancellable`` being set to ``true``. ``killed_by_us`` Set to ``true`` if the process has been killed by mpv as a result of ``cancellable`` being set to ``true``. ``utils.subprocess_detached(t)`` Runs an external process and detaches it from mpv's control. The parameter ``t`` is a table. The function reads the following entries: ``args`` Array of strings of the same semantics as the ``args`` used in the ``subprocess`` function. The function returns ``nil``. ``utils.parse_json(str [, trail])`` Parses the given string argument as JSON, and returns it as a Lua table. On error, returns ``nil, error``. (Currently, ``error`` is just a string reading ``error``, because there is no fine-grained error reporting of any kind.) The returned value uses similar conventions as ``mp.get_property_native()`` to distinguish empty objects and arrays. If the ``trail`` parameter is ``true`` (or any value equal to ``true``), then trailing non-whitespace text is tolerated by the function, and the trailing text is returned as 3rd return value. (The 3rd return value is always there, but with ``trail`` set, no error is raised.) ``utils.format_json(v)`` Format the given Lua table (or value) as a JSON string and return it. On error, returns ``nil, error``. (Errors usually only happen on value types incompatible with JSON.) The argument value uses similar conventions as ``mp.set_property_native()`` to distinguish empty objects and arrays. ``utils.to_string(v)`` Turn the given value into a string. Formats tables and their contents. This doesn't do anything special; it is only needed because Lua is terrible. Events ------ Events are notifications from player core to scripts. You can register an event handler with ``mp.register_event``. Note that all scripts (and other parts of the player) receive events equally, and there's no such thing as blocking other scripts from receiving events. Example: :: function my_fn(event) print("start of playback!") end mp.register_event("file-loaded", my_fn) List of events -------------- ``start-file`` Happens right before a new file is loaded. When you receive this, the player is loading the file (or possibly already done with it). ``end-file`` Happens after a file was unloaded. Typically, the player will load the next file right away, or quit if this was the last file. The event has the ``reason`` field, which takes one of these values: ``eof`` The file has ended. This can (but doesn't have to) include incomplete files or broken network connections under circumstances. ``stop`` Playback was ended by a command. ``quit`` Playback was ended by sending the quit command. ``error`` An error happened. In this case, an ``error`` field is present with the error string. ``redirect`` Happens with playlists and similar. Details see ``MPV_END_FILE_REASON_REDIRECT`` in the C API. ``unknown`` Unknown. Normally doesn't happen, unless the Lua API is out of sync with the C API. (Likewise, it could happen that your script gets reason strings that did not exist yet at the time your script was written.) ``file-loaded`` Happens after a file was loaded and begins playback. ``seek`` Happens on seeking. (This might include cases when the player seeks internally, even without user interaction. This includes e.g. segment changes when playing ordered chapters Matroska files.) ``playback-restart`` Start of playback after seek or after file was loaded. ``idle`` Idle mode is entered. This happens when playback ended, and the player was started with ``--idle`` or ``--force-window``. This mode is implicitly ended when the ``start-file`` or ``shutdown`` events happen. ``tick`` Called after a video frame was displayed. This is a hack, and you should avoid using it. Use timers instead and maybe watch pausing/unpausing events to avoid wasting CPU when the player is paused. ``shutdown`` Sent when the player quits, and the script should terminate. Normally handled automatically. See `Details on the script initialization and lifecycle`_. ``log-message`` Receives messages enabled with ``mp.enable_messages``. The message data is contained in the table passed as first parameter to the event handler. The table contains, in addition to the default event fields, the following fields: ``prefix`` The module prefix, identifies the sender of the message. This is what the terminal player puts in front of the message text when using the ``--v`` option, and is also what is used for ``--msg-level``. ``level`` The log level as string. See ``msg.log`` for possible log level names. Note that later versions of mpv might add new levels or remove (undocumented) existing ones. ``text`` The log message. The text will end with a newline character. Sometimes it can contain multiple lines. Keep in mind that these messages are meant to be hints for humans. You should not parse them, and prefix/level/text of messages might change any time. ``get-property-reply`` Undocumented (not useful for Lua scripts). ``set-property-reply`` Undocumented (not useful for Lua scripts). ``command-reply`` Undocumented (not useful for Lua scripts). ``client-message`` Undocumented (used internally). ``video-reconfig`` Happens on video output or filter reconfig. ``audio-reconfig`` Happens on audio output or filter reconfig. The following events also happen, but are deprecated: ``tracks-changed``, ``track-switched``, ``pause``, ``unpause``, ``metadata-update``, ``chapter-change``. Use ``mp.observe_property()`` instead. Extras ------ This documents experimental features, or features that are "too special" to guarantee a stable interface. ``mp.add_hook(type, priority, fn)`` Add a hook callback for ``type`` (a string identifying a certain kind of hook). These hooks allow the player to call script functions and wait for their result (normally, the Lua scripting interface is asynchronous from the point of view of the player core). ``priority`` is an arbitrary integer that allows ordering among hooks of the same kind. Using the value 50 is recommended as neutral default value. ``fn`` is the function that will be called during execution of the hook. See `Hooks`_ for currently existing hooks and what they do - only the hook list is interesting; handling hook execution is done by the Lua script function automatically.