.. _pythonreference:

Python Reference
================

VapourSynth is separated into a core library and a Python module. This section
explains how the core library is exposed through Python and some of the
special things unique to Python scripting, such as slicing and output.

.. note::

   Any script executed through the vsscript api (that means vspipe, avfs, vsvfw or
   other API users) will have __name__ set to "__vapoursynth__" unlike normal Python
   scripts where it usually is "__main__".

VapourSynth Structure
#####################

Most operations in the VapourSynth library are performed through the core object.
This core may load plugins, which all end up in their own unit,
or namespace, so to say, to avoid naming conflicts in the contained functions.
For this reason you call a plugin function with *core.unit.Function()*.

All arguments to functions have names that are lowercase and all function names
are CamelCase. Unit names are also lowercase and usually short. This is good to
remember.

Slicing and Other Syntactic Sugar
#################################

The VideoNode class (always called "clip" in practice) supports the full
range of indexing and slicing operations in Python. If you do perform a slicing
operation on a clip, you will get a new clip back with the desired frames.
Note that frame numbers, like python arrays, start counting at 0.
Here are a few examples.

Make a single frame clip containing frame number 5::

   video = clip[5]
   
Make a clip containing frames 6 to 9 (unlike Trim, the end value of python slicing is not inclusive)::

   video = clip[6:10]

Select even numbered frames::

   video = clip[::2]
   
Select odd numbered frames::

   video = clip[1::2]

Negative step is also allowed, so this reverses a clip::

   video = clip[::-1]

It may all be combined at once to confuse people, just like normal Python slicing::

   video = clip[-400:-800:-5]

Filters can be chained with a dot, it mostly works like Avisynth::

   clip = core.ffms2.Source("asdf.mov")
   clip = clip.std.Trim(first=100, last=2000).std.FlipVertical()

The addition operator can be used to splice clips together::

   clip4 = clip1 + clip2 + clip3

Which is equivalent to::

   clip4 = core.std.Splice([core.std.Splice([clip1, clip2], mismatch=False), clip3], mismatch=False)

The multiplication operator can be used to loop a clip::

   clip = clip * 42

Which is equivalent to::

   clip = core.std.Loop(clip, times=42)
   
Note that multiplication by 0 is a special case that will repeat the clip up to the maximum frame count.

Python Keywords as Filter Arguments
###################################

If a filter's argument happens to be a Python keyword, you may prepend
an underscore to the argument's name when invoking the filter. The Python
module will strip one leading underscore from all filter arguments before
passing them to the filters.

::

   clip = core.plugin.Filter(clip, _lambda=1)

Another way to deal with such arguments is to place them in a dictionary::

   args = { "lambda": 1 }
   clip = core.plugin.Filter(clip, **args)
   
VapourSynth will also support the PEP8 convention of using a single trailing
underscore to prevent collisions with python keywords.

Windows File Paths (Strings With Backslashes)
#############################################

If you have a string containing backslashes, you must either prefix the
string with "r", or duplicate every single backslash. The reason is
that the backslash is an escape character in Python.

Incorrect; Python will think "\\A" and "\\G" are supposed to mean
something special::

   core.avs.LoadPlugin("B:\Avisynth plugins\GuavaComb.dll")

Correct; Python will think "\\\\" means something special, namely a
single backslash::

   core.avs.LoadPlugin("B:\\Avisynth plugins\\GuavaComb.dll")

Correct; Python will not consider any combination of characters special::

   core.avs.LoadPlugin(r"B:\Avisynth plugins\GuavaComb.dll")

Additionally, if the string is a Windows file path, it can also be
written with forward slashes instead of backslashes::

   core.avs.LoadPlugin("B:/Avisynth plugins/GuavaComb.dll")

Output
######

The normal way of specifying the clip(s) to output is to call
*clip.set_output()*. All standard VapourSynth components only use output
index 0, except for vspipe where it's configurable but defaults to 0.
There are also other variables that can be set to control how a format is
output. For example, setting *enable_v210=True* changes the packing of the
YUV422P10 format to one that is common in professional software (like Adobe
products).
An example on how to get v210 output::

   some_clip = core.resize.Bicubic(clip, format=vs.YUV422P10)
   some_clip.set_output()
   enable_v210 = True

Raw Access to Frame Data
########################

The VideoFrame class simply contains one picture and all the metadata
associated with it. It is possible to access the raw data using ctypes and
some persistence. The three relevant functions are *get_read_ptr(plane)*,
*get_write_ptr(plane)*, and *get_stride(plane)*, all of which take the plane
to access as an argument. Accessing the data is a bit trickier as
*get_read_ptr()* and *get_write_ptr()* only return a pointer.

To get a frame simply call *get_frame(n)* on a clip. Should you desire to get
all frames in a clip, use this code::

   for frame in clip.frames():
       # Do stuff with your frame
       pass

Classes and Functions
#####################
.. py:attribute:: core

   Gets the singleton Core object. If it is the first time the function is called,
   the Core will be instantiated with the default options. This is the preferred
   way to reference the core.

.. py:function:: get_core([threads = 0, add_cache = True])

   Deprecated, use the *core* attribute instead.

   Get the singleton Core object. If it is the first time the function is called,
   the Core will be instantiated with the given options. If the Core has already
   been instantiated, all options are ignored. Setting *threads* to a value
   greater than zero overrides the autodetection.

.. py:function:: set_message_handler(handler_func)

   Sets a function to handle all debug output and fatal errors. The function should have the form *handler(level, message)*,
   where level corresponds to the vapoursynth.mt constants. Passing *None* restores the default handler, which prints to stderr.

.. py:function:: get_outputs()

   Return a read-only mapping of all outputs registered on the current node.

   The mapping will automatically update when a new output is registered.
   
.. py:function:: get_output([index = 0])

   Get a previously set output node. Throws an error if the index hasn't been
   set. Will return an AlphaOutputTuple when *alpha* was passed to *VideoNode.set_output*.

.. py:function:: clear_output([index = 0])

   Clears a clip previously set for output.

.. py:function:: clear_outputs()

   Clears all clips set for output in the current environment.
   
.. py:function:: construct_signature(signature[, injected=None])

   Creates a *inspect.Signature* object for the given registration signature.
   
   If *injected* is not None, the default of the first argument of the signature will be replaced with the value supplied with injected.
   

.. py:class:: Core

   The *Core* class uses a singleton pattern. Use the *core* attribute to obtain an
   instance. All loaded plugins are exposed as attributes of the core object.
   These attributes in turn hold the functions contained in the plugin.
   Use *get_plugins()* to obtain a full list of all currently loaded plugins
   you may call this way.
   
   .. py:attribute:: num_threads
      
      The number of concurrent threads used by the core. Can be set to change the number. Setting to a value less than one makes it default to the number of hardware threads.
      
   .. py:attribute:: add_cache
   
      For debugging purposes only. When set to *False* no caches will be automatically inserted between filters.
      
   .. py:attribute:: max_cache_size
   
      Set the upper framebuffer cache size after which memory is aggressively
      freed. The value is in megabytes.

   .. py:method:: set_max_cache_size(mb)
   
      Deprecated, use *max_cache_size* instead.

   .. py:method:: get_plugins()

      Returns a dict containing all loaded plugins and their functions.

   .. py:method:: list_functions()

      Works similar to *get_plugins()* but returns a human-readable string.

   .. py:method:: register_format(color_family, sample_type, bits_per_sample, subsampling_w, subsampling_h)

      Register a new Format object or obtain a reference to an existing one if
      it has already been registered. Invalid formats throw an exception.

   .. py:method:: get_format(id)

      Retrieve a Format object corresponding to the specified id. Returns None if there is no format with that *id*.

   .. py:method:: version()

      Returns version information as a string.
      
   .. py:method:: version_number()

      Returns the core version as a number.

.. py:class:: VideoNode

   Represents a video clip. The class itself supports indexing and slicing to
   perform trim, reverse and selectevery operations. Several operators are also
   defined for the VideoNode class: addition appends clips and multiplication
   repeats them. Note that slicing and indexing always return a new VideoNode
   object and not a VideoFrame.

   .. py:attribute:: format

      A Format object describing the frame data. If the format can change
      between frames, this value is None.

   .. py:attribute:: width

      The width of the video. This value will be 0 if the width and height can
      change between frames.

   .. py:attribute:: height

      The height of the video. This value will be 0 if the width and height can
      change between frames.

   .. py:attribute:: num_frames

      The number of frames in the clip.

   .. py:attribute:: fps

      The framerate represented as a *Fraction*. It is 0/1 when the clip has a variable
      framerate.
      
   .. py:attribute:: fps_num
   
      Deprecated, use *fps.numerator* instead

      The numerator of the framerate. If the clip has variable framerate, the
      value will be 0.

   .. py:attribute:: fps_den
   
      Deprecated, use *fps.denominator* instead

      The denominator of the framerate. If the clip has variable framerate, the
      value will be 0.

   .. py:attribute:: flags

      Special flags set for this clip. This attribute should normally be
      ignored.

   .. py:method:: get_frame(n)

      Returns a VideoFrame from position *n*.

   .. py:method:: get_frame_async(n)

      Returns a concurrent.futures.Future-object which result will be a VideoFrame instance or sets the
      exception thrown when rendering the frame.

      *The future will always be in the running or completed state*

   .. py:method:: get_frame_async_raw(n, cb: callable)

      First form of this method. It will call the callback from another thread as soon as the frame is rendered.

      The `result`-value passed to the callback will either be a VideoFrame-instance on success or a Error-instance
      on failure.

      *This method is intended for glue code. For normal use, use get_frame_async instead.*

      :param n: The frame number
      :param cb: A callback in the form `cb(node, n, result)`

   .. py:method:: get_frame_async_raw(n, cb: Future[, wrapper: callable = None])
      :noindex:

      Second form of this method. It will take a Future-like object (including asyncio.Future or similar)
      and set its result or exception according to the result of the function.

      The optional `wrapper`-parameter is intended for calls like asyncio.EventLoop.call_soon_threadsafe in which
      all calls to its future-object must be wrapped.

      *This method is intended for glue code. For normal use, use get_frame_async instead.*

      :param n: The frame number
      :param cb: The future-object whose result will be set.
      :param wrapper: A wrapper-callback which is responsible for moving the result across thread boundaries. If not
                      given, the result of the future will be set in a random thread.

   .. py:method:: set_output(index = 0, alpha = None)

      Set the clip to be accessible for output. This is the standard way to
      specify which clip(s) to output. All VapourSynth tools (vsvfw, vsfs,
      vspipe) use the clip in *index* 0. It's possible to specify an additional
      containing the *alpha* to output at the same time. Currently only vspipe
      takes *alpha* into consideration when outputting.

   .. py:method:: output(fileobj[, y4m = False, prefetch = 0, progress_update = None])
 
      Write the whole clip to the specified file handle. It is possible to pipe to stdout by specifying *sys.stdout* as the file.
      YUV4MPEG2 headers will be added when *y4m* is true.
      The current progress can be reported by passing a callback function of the form *func(current_frame, total_frames)* to *progress_update*.
      The *prefetch* argument is only for debugging purposes and should never need to be changed.

   .. py:method:: frames()

      Returns a generator iterator of all VideoFrames in the clip.

.. py:class:: AlphaOutputTuple

      This class is returned by get_output. If a *alpha* was passed to set_output, *get_output* will return an object of this type.
      
      .. py:attribute:: clip
      
         A VideoNode-instance containing the color planes.
         
      .. py:attribute:: alpha
      
         A VideoNode-instance containing the alpha planes.
      
.. py:class:: VideoFrame

      This class represents a video frame and all metadata attached to it.

   .. py:attribute:: format

      A Format object describing the frame data.

   .. py:attribute:: width

      The width of the frame.

   .. py:attribute:: height

      The height of the frame.

   .. py:attribute:: readonly

      If *readonly* is True, the frame data and properties cannot be modified.

   .. py:attribute:: props

      This attribute holds all the frame's properties as a dict. They are also mapped as sub-attributes for compatibility with older scripts.

   .. py:method:: copy()

      Returns a writable copy of the frame.

   .. py:method:: get_read_ptr(plane)

      Returns a pointer to the raw frame data. The data may not be modified.
      
   .. py:method:: get_read_array(plane)

      Returns a memoryview of the frame data that's only valid as long as the VideoFrame object exists. The data may not be modified.

   .. py:method:: get_write_ptr(plane)

      Returns a pointer to the raw frame data. It may be modified using ctypes
      or some other similar python package.
      
   .. py:method:: get_write_array(plane)

      Returns a memoryview of the frame data that's only valid as long as the VideoFrame object exists.

   .. py:method:: get_stride(plane)

      Returns the stride between lines in a *plane*.

.. py:class:: Format

   This class represents all information needed to describe a frame format. It
   holds the general color type, subsampling, number of planes and so on.
   The names map directly to the C API so consult it for more detailed
   information.

   .. py:attribute:: id

      A unique *id* identifying the format.

   .. py:attribute:: name

      A human readable name of the format.

   .. py:attribute:: color_family

      Which group of colorspaces the format describes.

   .. py:attribute:: sample_type

      If the format is integer or floating point based.

   .. py:attribute:: bits_per_sample

      How many bits are used to store one sample in one plane.

   .. py:attribute:: bytes_per_sample

      The actual storage is padded up to 2^n bytes for efficiency.

   .. py:attribute:: subsampling_w

      The subsampling for the second and third plane in the horizontal
      direction.

   .. py:attribute:: subsampling_h

      The subsampling for the second and third plane in the vertical direction.

   .. py:attribute:: num_planes

      The number of planes the format has.

   .. py:method:: replace(core=None, **kwargs)

      Returns a new format with the given modifications.

      The only supported attributes that can be replaced are `color_family`,
      `sample_type`, `bits_per_sample`, `subsampling_w`, `subsampling_h`.

      The optional `core`-parameter defines on which core the new format
      should be registered. This is usually not needed and defaults
      to the core of the current environment.

.. py:class:: Plugin

   Plugin is a class that represents a loaded plugin and its namespace.
   
   .. py:attribute:: name

      The namespace of the plugin.

   .. py:method:: get_functions()

      Returns a dict containing all the functions in the plugin. You can access
      it by calling *core.std.get_functions()*. Replace *std* with the namespace
      of the plugin you want to query.

   .. py:method:: list_functions()

      Works similar to *get_functions()* but returns a human-readable string.
      
.. py:class:: Function

   Function is a simple wrapper class for a function provided by a VapourSynth plugin.
   Its main purpose is to be called and nothing else.
   
   .. py:attribute:: name

      The function name. Identical to the string used to register the function.
      
   .. py:attribute:: plugin

      The *Plugin* object the function belongs to.
      
   .. py:attribute:: signature

      Raw function signature string. Identical to the string used to register the function.
   
.. py:class:: Environment

   This class represents an environment.

   Some editors allow multiple vapoursynth-scripts to run in the same process, each of them comes with a different Core-instance and
   their own set of outputs. Each core-instance with their associated outputs represent their own environment.

   At any given time, only one environment can be active (in the same context). This class allows introspection about
   environments and allows to switch to them at will.

   .. code::

        env = get_current_environment()
        # sometime later
        with env.use():
          # Do stuff inside this env.

   .. warning::

      Environment-objects obtained using the :func:`vpy_current_environment` can directly be used as
      as a context manager. This can cuase undefined behaviour when used in combination with generators and/or
      coroutines.

      This context-manager maintains a thread-local environment-stack that is used to restore the previous environment.
      This can cause issues if the frame is suspended inside the block.

      A similar problem also existed in previous VapourSynth versions!
      
      .. code::

         env = vpy_current_environment()
         with env:
              yield

   .. py:function:: is_single()

      Returns True if the script is _not_ running inside a vsscript-Environment.
      If it is running inside a vsscript-Environment, it returns False.

   .. py:attribute:: env_id

      Return -1 if the script is not running inside a vsscript-Environment.
      Otherwise, it will return the current environment-id.

   .. py:attribute:: single

      See is_single()

   .. py:attribute:: alive

      Has the environment been destroyed by the underlying application?

   .. py:method:: copy

      Creates a copy of the environment-object.

      Added: R50

   .. py:method:: use

      Returns a context-manager that enables the given environment in the block enclosed in the with-statement and restores the environment to the one
      defined before the with-block has been encountered.

      .. code::
      
         env = vpy_current_environment()
         with env.use():
             with env.use():
                 pass

      Added: R50

.. py:function:: vpy_current_environment()

   Deprecated. Use :func:`get_current_environment` instead.

   Returns an Environment-object representing the environment the script is currently running in. It will raise an error if we are currently not inside any
   script-environment while vsscript is being used.

   This function is intended for Python-based editors using vsscript.
   This function has been deprecated as this function has undefined behaviour when used together with generators or coroutines.

.. py:function:: get_current_environment()

   Returns an Environment-object representing the environment the script is currently running in. It will raise an error if we are currently not inside any
   script-environment while vsscript is being used.

   This function is intended for Python-based editors using vsscript.

   Added: R50

.. py:class:: EnvironmentPolicy

   This class is intended for subclassing by custom Script-Runners and Editors.
   Normal users don't need this class. Most methods implemented here have corresponding APIs in other parts of this module.
   
   An instance of this class controls which environment is activated in the current context.
   The exact meaning of "context" is defined by the concrete EnvironmentPolicy. A environment is represented by a :class:`EnvironmentData`-object.

   To use this class, first create a subclass and then use :func:`register_policy` to get VapourSynth to use your policy. This must happen before vapoursynth is first
   used. VapourSynth will automatically register an internal policy if it needs one. The subclass must be weak-referenciable!
   
   Once the method :meth:`on_policy_registered` has been called, the policy is responsible for creating and managing environments.

   Special considerations have been made to ensure the functions of class cannot be abused. You cannot retrieve the current running policy youself.
   The additional API exposed by "on_policy_registered" is only valid if the policy has been registered.
   Once the policy is unregistered, all calls to the additional API will fail with a RuntimeError.

   Added: R50

   .. py:method:: on_policy_registered(special_api)

      This method is called when the policy has successfully been registered. It proivdes additional internal methods that are hidden as they are useless and or harmful
      unless you implement your own policy.

      :param special_api: This is a :class:`EnvironmentPolicyAPI`-object that exposes additional API

   .. py:method:: on_policy_cleared()

      This method is called once the python-process exits or when unregister_policy is called by the environment-policy. This allows the policy to free the resources
      used by the policy.
   
   .. py:method:: get_current_environment()

      This method is called by the module to detect which environment is currently running in the current context.

      :returns: An :class:`EnvironmentData`-object representing the currently active environment in the current context.

   .. py:method:: set_environment(environment)

      This method is called by the module to change the currently active environment.

      :param environment: The :class:`EnvironmentData` to enable in the current context.
      :returns: The environment that was enabled previously.

   .. py:method:: is_alive(environment)

      Is the current environment still active and managed by the policy.

.. py:class:: EnvironmentPolicyAPI

   This class is intended to be used by custom Script-Runners and Editors. An instance of this class exposes an additional API.
   The methods are bound to a specific :class:`EnvironmentPolicy`-instance and will only work if the policy is currenty registered.

   Added: R50

   .. py:method:: wrap_environment(environment)

      Creates a new :class:`Environment`-object bound to the passed environment-id.

      .. warning::

         This function does not check if the id corresponds to a live environment as the caller is expected to know which environments are active.

   .. py:method:: create_environment()
   
      Returns a :class:`Environment` that is used by the wrapper for context sensitive data used by VapourSynth.
      For example it holds the currently active core object as well as the currently registered outputs.

   .. py:method:: unregister_policy()

      Unregisters the policy it is bound to and allows another policy to be registered.

.. py:function:: register_policy(policy)

   This function is intended for use by custom Script-Runners and Editors. It installs your custom :class:`EnvironmentPolicy`. This function only works if no other policy has been
   installed.

   If no policy is installed, the first environment-sensitive call will automatically register an internal policy.

   Added: R50
   
   .. note::

      This must be done before VapourSynth is used in any way. Here is a non-exhaustive list that automatically register a policy:

      * Using "vsscript_init" in "VSScript.h"
      * Using :func:`get_core`
      * Using :func:`get_outputs`
      * Using :func:`get_output`
      * Using :func:`clear_output`
      * Using :func:`clear_outputs`
      * Using :func:`vpy_current_environment`
      * Using :func:`get_current_environment`
      * Accessing any attribute of :attr:`core`

.. py:function:: has_policy()

   This function is intended for subclassing by custom Script-Runners and Editors. This function checks if a :class:`EnvironmentPolicy` has been installed.

   Added: R50

.. py:attribute:: _using_vsscript

   INTERNAL ATTRIBUTE. Deprecated (will be removed soon). This was the only way to find out if VSScript.h was calling this script.
   It now stores true if a custom policy is installed or VSScript.h is used. Use :func:`has_policy` instead.


.. py:class:: EnvironmentData

   Internal class that stores the context sensitive data that VapourSynth needs. It is an opaque object whose attributes you cannot access directly.

   A normal user has no way of getting an instance of this object. You can only encounter EnvironmentData-objects if you work with EnvironmentPolicies.

   This object is weak-referenciable meaning you can get a callback if the environment-data object is actually being freed (i.e. no other object holds an instance
   to the environment data.)

   Added: R50

.. py:class:: Func

   Func is a simple wrapper class for VapourSynth VSFunc objects.
   Its main purpose is to be called and manage reference counting.

.. py:exception:: Error

   The standard exception class. This exception is thrown on most errors
   encountered in VapourSynth.

Color Family Constants
######################

The color family constants describe groups of formats and the basic way their
color information is stored. You should be familiar with all of them apart from
maybe *YCOCG* and *COMPAT*. The latter is a special junk category for non-planar
formats. These are the declared constants in the module::

   RGB
   YUV
   GRAY
   YCOCG
   COMPAT

Format Constants
################

Format constants exactly describe a format. All common and even more uncommon
formats have handy constants predefined so in practice no one should really
need to register one of their own. These values are mostly used by the resizers
to specify which format to convert to. The naming system is quite simple. First
the color family, then the subsampling (only YUV has it) and after that how many
bits per sample in one plane. The exception to this rule is RGB, which has the
bits for all 3 planes added together. The long list of values::

   GRAY8
   GRAY16
   GRAYH
   GRAYS

   YUV420P8
   YUV422P8
   YUV444P8
   YUV410P8
   YUV411P8
   YUV440P8

   YUV420P9
   YUV422P9
   YUV444P9

   YUV420P10
   YUV422P10
   YUV444P10

   YUV420P12
   YUV422P12
   YUV444P12
   
   YUV420P14
   YUV422P14
   YUV444P14
   
   YUV420P16
   YUV422P16
   YUV444P16

   YUV444PH
   YUV444PS

   RGB24
   RGB27
   RGB30
   RGB48

   RGBH
   RGBS

   COMPATBGR32
   COMPATYUY2

Sample Type Constants
#####################

::

   INTEGER
   FLOAT
