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AnyEvent-MPV-0.2
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/ AnyEvent::MPV

NAME

AnyEvent::MPV - remote control mpv (https://mpv.io)

SYNOPSIS

use AnyEvent::MPV;

DESCRIPTION

This module allows you to remote control mpv (a video player). It also is an AnyEvent user, you need to make sure that you use and run a supported event loop.

There are other modules doing this, and I haven't looked much at them other than to decide that they don't handle encodings correctly, and since none of them use AnyEvent, I wrote my own. When in doubt, have a look at them, too.

Knowledge of the mpv command interface is required to use this module.

Features of this module are:

uses AnyEvent, so integrates well into most event-based programs
supports asynchronous and synchronous operation
allows you to properly pass binary filenames
accepts data encoded in any way (does not crash when mpv replies with non UTF-8 data)
features a simple keybind/event system

OVERVIEW OF OPERATION

This module forks an mpv process and uses --input-ipc-client (or equivalent) to create a bidirectional communication channel between it and the mpv process.

It then speaks the somewhat JSON-looking (but not really being JSON) protocol that mpv implements to both send it commands, decode and handle replies, and handle asynchronous events.

Here is a very simple client:

use AnyEvent;
use AnyEvent::MPV;

my $videofile = "./xyzzy.mp4";

my $mpv = AnyEvent::MPV->new (trace => 1);

$mpv->start ("--", $videofile);

my $timer = AE::timer 2, 0, my $quit = AE::cv;
$quit->recv;

This starts mpv with the two arguments -- and $videofile, which it should load and play. It then waits two seconds by starting a timer and quits. The trace argument to the constructor makes mpv more verbose and also prints the commands and responses, so you can have an idea what is going on.

In my case, the above example would output something like this:

[uosc] Disabled because original osc is enabled!
mpv> {"event":"start-file","playlist_entry_id":1}
mpv> {"event":"tracks-changed"}
 (+) Video --vid=1 (*) (h264 480x480 30.000fps)
mpv> {"event":"metadata-update"}
mpv> {"event":"file-loaded"}
Using hardware decoding (nvdec).
mpv> {"event":"video-reconfig"}
VO: [gpu] 480x480 cuda[nv12]
mpv> {"event":"video-reconfig"}
mpv> {"event":"playback-restart"}

This is not usually very useful (you could just run mpv as a simple shell command), so let us load the file at runtime:

use AnyEvent;
use AnyEvent::MPV;

my $videofile = "./xyzzy.mp4";

my $mpv = AnyEvent::MPV->new (
   trace => 1,
   args  => ["--pause", "--idle=yes"],
);

$mpv->start;
$mpv->cmd_recv (loadfile => $mpv->escape_binary ($videofile));
$mpv->cmd ("set", "pause", "no");

my $timer = AE::timer 2, 0, my $quit = AE::cv;
$quit->recv;

This specifies extra arguments in the constructor - these arguments are used every time you ->start mpv, while the arguments to ->start are only used for this specific clal to0 start. The argument --pause keeps mpv in pause mode (i.e. it does not play the file after loading it), and --idle=yes tells mpv to not quit when it does not have a playlist - as no files are specified on the command line.

To load a file, we then send it a loadfile command, which accepts, as first argument, the URL or path to a video file. To make sure mpv does not misinterpret the path as a URL, it was prefixed with ./ (similarly to "protecting" paths in perls open).

Since commands send to mpv are send in UTF-8, we need to escape the filename (which might be in any encoding) using the esscape_binary method - this is not needed if your filenames are just ascii, or magically get interpreted correctly, but if you accept arbitrary filenamews (e.g. from the user), you need to do this.

The cmd_recv method then queues the command, waits for a reply and returns the reply data (or croaks on error). mpv would, at this point, load the file and, if everything was successful, show the first frame and pause. Note that, since mpv is implement rather synchronously itself, do not expect commands to fail in many circumstances - for example, fit he file does not exit, you will likely get an event, but the loadfile command itself will run successfully.

To unpause, we send another command, set, to set the pause property to no, this time using the cmd method, which queues the command, but instead of waiting for a reply, it immediately returns a condvar that cna be used to receive results.

This should then cause mpv to start playing the video.

It then again waits two seconds and quits.

Now, just waiting two seconds is rather, eh, unuseful, so let's look at receiving events (using a somewhat embellished example):

use AnyEvent;
use AnyEvent::MPV;

my $videofile = "xyzzy.mp4";

my $quit = AE::cv;

my $mpv = AnyEvent::MPV->new (
   trace => 1,
   args  => ["--pause", "--idle=yes"],
   on_event => sub {
      my ($mpv, $event, $data) = @_;

      if ($event eq "start-file") {
         $mpv->cmd ("set", "pause", "no");
      } elsif ($event eq "end-file") {
         print "end-file<$data->{reason}>\n";
         $quit->send;
      }
   },
);

$mpv->start;
$mpv->cmd (loadfile => $mpv->escape_binary ($videofile));

$quit->recv;

This example uses a global condvar $quit to wait for the file to finish playing. Also, most of the logic is now in an on_event callback, which receives an event name and the actual event object.

The two events we handle are start-file, which is emitted by mpv once it has loaded a new file, and end-file, which signals the end of a file.

In the former event, we again set the pause property to no so the movie starts playing. For the latter event, we tell the main program to quit by invoking $quit.

This should conclude the basics of operation. There are a few more examples later in the documentation.

ENCODING CONVENTIONS

As a rule of thumb, all data you pass to this module to be sent to mpv is expected to be in unicode. To pass something that isn't, you need to escape it using escape_binary.

Data received from $mpv, however, is not decoded to unicode, as data returned by mpv is not generally encoded in unicode, and the encoding is usually unspecified. So if you receive data and expect it to be in unicode, you need to first decode it from UTF-8, but note that this might fail. This is not a limitation of this module - mpv simply does not specify nor guarantee a specific encoding, or any encoding at all, in its protocol.

METHODS

$mpv = AnyEvent::MPV->new (key => value...)

Creates a new mpv object, but does not yet do anything. The support key-value pairs are:

mpv => $path

The path to the mpv binary to use - by default, mpv is used and therefore, uses your PATH to find it.

args => [...]

Arguments to pass to mpv. These arguments are passed after the hardcoded arguments used by this module, but before the arguments passed ot start. It does not matter whether you specify your arguments using this key, or in the start call, but when you invoke mpv multiple times, typically the arguments used for all invocations go here, while arguments used for specific invocations (e..g filenames) are passed to start.

trace => false|true|coderef

Enables tracing if true. In trace mode, output from mpv is printed to standard error using a mpv> prefix, and commands sent to mpv are printed with a >mpv prefix.

If a code reference is passed, then instead of printing to standard errort, this coderef is invoked with a first arfgument being either mpv> or >mpv, and the second argument being a string to display. The default implementation simply does this:

sub {
   warn "$_[0] $_[1]\n";
}
on_eof => $coderef->($mpv)
on_event => $coderef->($mpv, $event, $data)
on_key => $coderef->($mpv, $string)

These are invoked by the default method implementation of the same name - see below.

$string = $mpv->escape_binary ($string)

This module excects all command data sent to mpv to be in unicode. Some things are not, such as filenames. To pass binary data such as filenames through a comamnd, you need to escape it using this method.

The simplest example is a loadfile command:

$mpv->cmd_recv (loadfile => $mpv->escape_binary ($path));
$started = $mpv->start (argument...)

Starts mpv, passing the given arguemnts as extra arguments to mpv. If mpv is already running, it returns false, otherwise it returns a true value, so you can easily start mpv on demand by calling start just before using it, and if it is already running, it will not be started again.

The arguments passwd to mpv are a set of hardcoded built-in arguments, followed by the arguments specified in the constructor, followed by the arguments passwd to this method. The built-in arguments currently are --no-input-terminal, --really-quiet (or --quiet in trace mode), and --input-ipc-client (or equivalent).

Some commonly used and/or even useful arguments you might want to pass are:

--idle=yes or --idle=once to keep mpv from quitting when you don't specify a file to play.
--pause, to keep mpv from instantly starting to play a file, in case you want to inspect/change properties first.
--force-window=no (or similar), to keep mpv from instantly opening a window, or to force it to do so.
--audio-client-name=yourappname, to make sure audio streams are associated witht eh right program.
--wid=id, to embed mpv into another application.
--no-terminal, --no-input-default-bindings, --no-input-cursor, --input-conf=/dev/null, --input-vo-keyboard=no - to ensure only you control input.

The return value can be used to decide whether mpv needs initializing:

if ($mpv->start) {
   $mpv->bind_key (...);
   $mpv->cmd (set => property => value);
   ...
}

You can immediately starting sending commands when this method returns, even if mpv has not yet started.

$mpv->stop

Ensures that mpv is being stopped, by killing mpv with a TERM signal if needed. After this, you can ->start a new instance again.

$mpv->on_eof

This method is called when mpv quits - usually unexpectedly. The default implementation will call the on_eof code reference specified in the constructor, or do nothing if none was given.

For subclassing, see SUBCLASSING, below.

$mpv->on_event ($event, $data)

This method is called when mpv sends an asynchronous event. The default implementation will call the on_event code reference specified in the constructor, or do nothing if none was given.

The first/implicit argument is the $mpv object, the second is the event name (same as $data->{event}, purely for convenience), and the third argument is the event object as sent by mpv (sans event key). See List of events in its documentation.

For subclassing, see SUBCLASSING, below.

$mpv->on_key ($string)

Invoked when a key declared by ->bind_key is pressed. The default invokes the on_key code reference specified in the constructor with the $mpv object and the key name as arguments, or do nothing if none was given.

For more details and examples, see the bind_key method.

For subclassing, see SUBCLASSING, below.

$mpv->cmd ($command => $arg, $arg...)

Queues a command to be sent to mpv, using the given arguments, and immediately return a condvar.

See the mpv documentation for details on individual commands.

The condvar can be ignored:

$mpv->cmd (set_property => "deinterlace", "yes");

Or it can be used to synchronously wait for the command results:

$cv = $mpv->cmd (get_property => "video-format");
$format = $cv->recv;

# or simpler:

$format = $mpv->cmd (get_property => "video-format")->recv;

# or even simpler:

$format = $mpv->cmd_recv (get_property => "video-format");

Or you can set a callback:

$cv = $mpv->cmd (get_property => "video-format");
$cv->cb (sub {
   my $format = $_[0]->recv;
});

On error, the condvar will croak when recv is called.

$result = $mpv->cmd_recv ($command => $arg, $arg...)

The same as calling cmd and immediately recv on its return value. Useful when you don't want to mess with mpv asynchronously or simply needs to have the result:

$mpv->cmd_recv ("stop");
$position = $mpv->cmd_recv ("get_property", "playback-time");
$mpv->bind_key ($INPUT => $string)

This is an extension implement by this module to make it easy to get key events. The way this is implemented is to bind a client-message witha first argument of AnyEvent::MPV and the $string you passed. This $string is then passed to the on_key handle when the key is proessed, e.g.:

my $mpv = AnyEvent::MPV->new (
   on_key => sub {
      my ($mpv, $key) = @_;

      if ($key eq "letmeout") {
         print "user pressed escape\n";
      }
   },
);

$mpv_>bind_key (ESC => "letmeout");

The key configuration is lost when mpv is stopped and must be (re-)done after every start.

[$guard] = $mpv->observe_property ($name => $coderef->($mpv, $name, $value))
[$guard] = $mpv->observe_property_string ($name => $coderef->($mpv, $name, $value))

These methods wrap a registry system around mpv's observe_property and observe_property_string commands - every time the named property changes, the coderef is invoked with the $mpv object, the name of the property and the new value.

For a list of properties that you can observe, see the mpv documentation.

Due to the (sane :) way mpv handles these requests, you will always get a property cxhange event right after registering an observer (meaning you don't have to query the current value), and it is also possible to register multiple observers for the same property - they will all be handled properly.

When called in void context, the observer stays in place until mpv is stopped. In any otrher context, these methods return a guard object that, when it goes out of scope, unregisters the observe using unobserve_property.

Internally, this method uses observer ids of 2**52 (0x10000000000000) or higher - it will not interfere with lower ovserver ids, so it is possible to completely ignore this system and execute observe_property commands yourself, whilst listening to property-change events - as long as your ids stay below 2**52.

Example: register observers for changtes in aid and sid. Note that a dummy statement is added to make sure the method is called in void context.

sub register_observers {
   my ($mpv) = @_;

   $mpv->observe_property (aid => sub {
      my ($mpv, $name, $value) = @_;
      print "property aid (=$name) has changed to $value\n";
   });

   $mpv->observe_property (sid => sub {
      my ($mpv, $name, $value) = @_;
      print "property sid (=$name) has changed to $value\n";
   });

   () # ensure the above method is called in void context
}

SUBCLASSING

Like most perl objects, AnyEvent::MPV objects are implemented as hashes, with the constructor simply storing all passed key-value pairs in the object. If you want to subclass to provide your own on_* methods, be my guest and rummage around in the internals as much as you wish - the only guarantee that this module dcoes is that it will not use keys with double colons in the name, so youc an use those, or chose to simply not care and deal with the breakage.

If you don't want to go to the effort of subclassing this module, you can also specify all event handlers as constructor keys.

SEE ALSO

AnyEvent, the mpv command documentation.

AUTHOR

Marc Lehmann <schmorp@schmorp.de>
http://home.schmorp.de/