MLT Multimedia Framework

Author, manage, and run multitrack audio/video compositions.
The engine of a non-linear video editor that can be used in all sorts of apps, not just desktop video editors.
MLT is an open source multimedia framework, designed and developed for television broadcasting. It provides a toolkit for broadcasters, video editors, media players, transcoders, web streamers and many more types of applications. The functionality of the system is provided via an assortment of ready to use tools, XML authoring components, and an extensible plug-in based API.
Download source code. The easiest way to try out and learn MLT is by downloading Shotcut.

Recent News

v7.4.0 released

Dec 19, 2021

You can download it from GitHub.

This main highlight of this version is property animation for avfilter!


  • Added more constructors and assignment operators in C++ wrapper:
    • Mlt::Filter::Filter(Mlt::Filter*)
    • Mlt::Link::Link(Mlt::Link*)
    • Mlt::Link::Link(Mlt::Service&)
    • Mlt::Link::Link(Mlt::Link&)
    • Mlt::Link::Link(Mlt::Link const&)
    • Mlt::Link::operator=(Mlt::Link const&)
    • Mlt::Service::Service(Mlt::Service*)
  • Fixed serialized animation in mlt_animation_serialize_cut_tf() and mlt_animation_serialize_cut() to include a trailing keyframe value.


  • Added property animation for avfilter filters.
    This only works for numeric parameters, but many libavfilter options that have a type string are actually numeric in nature but accept a string expression.
  • Added rotate property to avformat producer to override orientation.
  • Changed jackrack module to silence false LADSPA plugin loading errors.
  • Fixed a crash in the oldfilm filter when using preview scaling.
  • Fixed timeremap link distorts audio when speed is zero.
  • Added nautical mile and knot units of measure to the gpstext filter.
  • Fixed full range color handling with embedded tractor (e.g. same track transition).
  • Fixed device capture in avformat producer regression in version 7.2.0.
  • Fixed a crash in the matte transition.

v7.2.0 released

Nov 1, 2021

You can download it from GitHub.

This is the first major maintenance release for the new major version 7 rendering it much more production ready. Plus there are a few nice new features.


  • Added support for mlt_properties as a child of mlt_properties including XML (de)serialization:
    • mlt_property_set_properties()
    • mlt_property_get_properties()
    • mlt_properties_set_properties()
    • mlt_properties_get_properties()
    • mlt_properties_get_properties_at)(
    • Mlt::Properties::set()
    • Mlt::Properties::get_props()
    • Mlt::Properties::get_props_at() Applications can use this to store structured data in its own namespace, for example “shotcut:markers”. And modules could use this for hierarchical parameters.
  • Fixed crash in mlt_transition upon inserting or removing a track.
  • Stopped loading mlt_profile until needed in mlt_chain creation.


  • Added filter gpstext that is similar to dynamictext based on data in a GPX file.
  • Added speed parameter to timer filter.
  • Added WebP presets for avformat consumer.
  • Added a pixelate option to the opencv_tracker filter’s blur property.
  • Fixed center_bias of crop filter not working with use_profile.
  • Fixed some missing RGB mlt_image_format renames after change in v7.0.0. This primarily affected presets and service metadata.
  • Fixed a crash when changing preview scaling in timeremap link.
  • Fixes problems due to adding redundant normalize filters upon loading a producer from XML.
  • Ensure filters added by the loader producer always come first in list.
  • Fixed a crash using shape and affine filters together on color producer.
  • Fixed a crash when a vidstab file fails to open.
  • Changed vidstab filter to save its file in ASCII text mode.
  • Fixed a clang LTO error in the decklink module.
  • Fixed a video decoding regression on some videos in the avformat producer.
  • Fixed a crash in the audiowaveform filter.
  • Fixed loading a relative filename from XML for mask_start with shape.
  • Fixed “#filedate#” in dynamictext filter when used with timeremap link.
  • Fixed timer filter’s new speed property interaction with start delay.
  • Fixed a crash with YUYV422 (YUY2) input in avformat producer.
  • Fixed data race condition in timeremap link.
  • Fixed compiling avformat module with FFmpeg git beyond v4.4 with many deprecations removed.
  • Fixed alpha channel size calculation in brightness filter.
  • Restore legacy tracker and the new DaSiam tracker for OpenCV >= 4.5.3 in the opencv_tracker filter.
  • Fixed a crash in opencv_tracker on shape_width = 0.
  • Fixed incorrect handling of in and out points and duration in the opencv_tracker filter.
  • Fixed the composite transition leaking left border of an image on the right side on uneven width.
  • Fixed a problem handling some UTF-8 in thhe typerwriter filter.


  • Added support for the RELOCATABLE CMake option for Linux or BSD build.

v7.0.1 released

May 15, 2021

You can download it from GitHub.

This version is just build fixes for the most immediate problems with the somewhat new but exclusive build system in v7.

  • Fixed docker image not working.
  • Fixed a system-installed build cannot finds its modules and data.
  • Fixed the python installation path for binaries.
  • Added support for the DESTDIR environment variable when creating melt symlink.
  • Increased the build constant for the maximum size of a line of a properties file.
  • Fixed the vid.stab metadata install path.

v7.0.0 released

May 2, 2021

You can download it from GitHub.

This is a major new version that breaks API to add a major new feature to the framework: retiming. This is accomplished through new classes mlt_chain and mlt_link. And since we are breaking API we decided to clean house by removing deprecations and switching the build system over entirely to CMake. For more information see our migration guide. More documentation about the new chain and link classes is still pending.


  • Added mlt_chain and Mlt::Chain classes.
  • Added mlt_link and Mlt::Link classes.
  • Added a link value to service type in the service metadata schema.
  • Added a boolean animation parameter attribute to the service metadata schema.
  • Added mlt_animation_shift_frame() and Mlt::Animation::shift_frames().
  • Added mlt_animation_get_string().
  • Fixed using a stale cached property animation string.
  • Added mlt_image and Mlt::Image classes.
  • Remove legacy “height + 1” workaround in image allocation.
  • Fixed a crash on setting timewarp speed higher than 23x.
  • Added mlt_audio_silence().
  • Removed mlt_image_opengl.
  • Replaced variadic arguments in mlt_events with new mlt_event_data APIs.
  • Removed mlt_geometry APIs.
  • Renamed mlt_image_rgb24a as mlt_image_rgba.
  • Renamed mlt_image_rgb24 to mlt_image_rgb.
  • Renamed mlt_image_glsl to mlt_image_movit.
  • Renamed mlt_image_glsl_texture to mlt_image_opengl_texture.
  • Removed virtual function mlt_frame::get_alpha_mask().
  • Removed mlt_frame_get_alpha_mask().
  • Removed deprecated functions:
    • mlt_sample_calculator
    • mlt_sample_calculator_to_now
    • mlt_channel_layout_name
    • mlt_channel_layout_id
    • mlt_channel_layout_channels
    • mlt_channel_layout_default
    • mlt_slices_init
    • mlt_slices_close
    • mlt_slices_run
    • mlt_playlist_move_region
    • Mlt::Playlist::move_region
  • Fixed a rounding error calculating display aspect ratio in mlt_profile_from_producer().


  • Added a timeremap link to the core module with animatable map property. (Speed can increase or decrease between keyframes including reverse.)
  • Added chain and link XML elements to xml module.
  • Added “” property to avformat producer.
  • Removed deprecated modules:
    • dv
    • gtk2 (not gdk)
    • kino
    • linsys
    • lumas
    • motion_est
    • swfdec
    • videostab
  • Removed the following services:
    • data_feed filter
    • data_show filter
    • region filter and transition
    • sdl_image
  • Converted filters to use new mlt_image class:
    • brightness
    • imageconver
    • mirror
    • spot_remover
  • Deprecated the audiowave filter.
  • Added the ability to build the jackrack module without JACK to get only LADSPA producers and filters.
  • Deprecated start and end properties for the following filters:
    • brightness
    • panner
    • boxblur
    • wave
    • volume
  • Removed deprecated font property from pango producer.
  • Improved album art (attached pic) detection in avformat producer.
  • Improved the resample filter to have less artifacts and use less memory.


  • CMake: nearly complete rewrite.
  • Removed the old configure bash scripts and Makefiles.
  • Added -chain and -link options to melt command line.

v6.26.1 released

Apr 10, 2021

You can download it from GitHub.

This is the last planned release of major version 6. Version 7 will be released soon and introduce some minor API breakage while removing deprecations. The main new feature in this version is hardware-accellerated decoding! However, this is a basic implementation: It always returns the uncompressed video to the CPU memory with no pipelining to filters. Even when coupled with hardware encoding in the avformat consumer it must transfer the video. Also, there is no automatic software/CPU fallback and no resource management.


  • Added support for hwaccel query string parameter to the avformat producer. It accepts the following values:
    vaapi (Linux/BSD), cuda (Linux), videotoolbox (macOS), d3d11va (Windows), dxva2 (Windows)
    The query string delimiter is a backslash followed by a question mark: \?. The backslash prevents interpreting the question mark from being a part of the file name. You must preface the file name with either avformat: or file: to make it work with melt (but not XML or via API because melt interprets name=value as a MLT property if there is no colon before equals).
  • Added support for hwaccel_device query string parameter to the avformat producer. This is only used with vaapi (device path) and cuda, d3d11va, or dxva (number).
  • Improved the usage of image slice threading in frei0r. This only applies when threads=0 and only works with some frei0r plugins that you must decide yourself.
  • Added an ellipse item to kdenlivetitle producer.
  • Added support for PNG and GIF as album art in the avformat producer.
  • Added BT.2020 color space metadata to the avformat producer.
  • Resolved many FFmpeg deprecations in the avformat producer making it possible to support AV1 decoding.
  • Added a strobe fitler that periodically makes the alpha channel transparent.
  • Added a new typewriter text filter (currently only works with the kdenlivetitle producer).
  • Improved sound quality for lower pitch shifts in rbpitch.
  • Fixed speed of trick play in the jack, rtaudio, sdl_audio, and sdl2_audio consumers.
  • Fixed matrix for independent channels in swresample filter.
  • Fixed leading zeros for the timer filter.
  • Fixed flickering using affine with a luma transition.
  • Fixed a crash using RGBA images in the qimage producer (regression in v6.22.0).
  • Fixed brightness filter misbehaves on alpha > 1.
  • Fixed writing flac format file does not set its duration in the avformat consumer.
  • Fixed an infinite loop in rbpitch filter.
  • Fixed ttl in the qimage producer.
  • Fixed building with OpenCV 4.5
  • Fixed artifacts with multiple HTML qtext filters and frame threading.
  • Deprecated the start and end properties on the following (use property animation instead):
    • brightness
    • panner
    • boxblur
    • wave
    • volume
  • Deprecated the following services:
    • data_show
    • region
    • transition filter
    • autotrack_rectangle
    • motion_est
    • slowmotion


  • CMake:
    • Fixed building without SWIG.
    • Added many “MOD_…” options to explictly disable modules.
    • Added src/tests and the option BUILD_TESTING, which defaults off.
    • All dependency checks moved to top level CMakeLists.txt.
    • Install melt man page.
    • Install oldfilm SVG files.
    • Added src/examples.
    • Install framework/metaschema.yaml.
    • Fixed plusgpl datadir.
    • Added all swwig/ languages.
    • Increased C++ standard to C++14.
  • Added an AV1 encoding preset.
  • Improved documentation of the requirement for C11.
  • The minimum version of FFmpeg is v4.0 and Libav is no longer supported.


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MLT enables you to author, manage, and run multitrack audio/video compositions.
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