Dudemanguy 296d40dc6f vo: fix race condition with redraw requests
There is a very subtle race in vo that can manifest itself on pause
events. In the renderloop, render_frame, unsurprisingly, does the heavy
lifting of actually queuing up and flipping the frames. This is called
during normal playback. Sometimes various parts of the player can make a
redraw request which will latter trigger another render of the frame
later down in the loop (do_redraw). Because these requests can happen at
essentially anytime, sometimes the redraw request will happen *before*
do_redraw and it'll be caught in render_frame. When this happens,
the existing render_frame run works perfectly fine as a redraw so it
clears out the request which is sensible. Normally this is all locked of
course, but there's one catch. render_frame has to unlock itself when
propagating down into specific VOs/backends. That's what causes this
bug.

While render_frame is unlocked, other parts of the player can send
redraw requests which will cause in->request_redraw to become true. The
logic in the code always clears out this parameter after a successful
render, but this isn't correct. When in->request_become becomes true in
the middle of render_frame, there needs to be one more draw afterwards
to reflect whatever actually changed (usually the OSD). Instead, this
gets simply discarded. If you rapidly spam pause while rendering things
to the OSD at the same time, it's possible to for the last render to
be behind a frame and appear as if your osd event was ignored.

Once you realize what is happening, the fix is quite simple. Just store
the initial value of in->request_redraw before the unlock step. After we
do the render step and unlock again, only set in->request_redraw to
false if there was an initial redraw request. We just finished doing a
redraw, so it is safe to clear. Otherwise, leave in->request_redraw
alone. If it is initially false, then it will still be false and nothing
changes. However if it updated to true in the middle of the rendering,
this value is now preserved so we can go and call do_redraw later and
show what that last frame was meant to be when you pause. One
unfortunate thing about this design is that it is technically possible
for other internal things in vo to update during that unlocked period.
Hopefully, that doesn't actually happen and only redraw requests work
like this.

Fixes #8172 and #8350.
2023-03-02 22:09:10 +00:00
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mpv logo

mpv

Overview

mpv is a free (as in freedom) media player for the command line. It supports a wide variety of media file formats, audio and video codecs, and subtitle types.

There is a FAQ.

Releases can be found on the release list.

System requirements

  • A not too ancient Linux, Windows 7 or later, or OSX 10.8 or later.
  • A somewhat capable CPU. Hardware decoding might help if the CPU is too slow to decode video in realtime, but must be explicitly enabled with the --hwdec option.
  • A not too crappy GPU. mpv's focus is not on power-efficient playback on embedded or integrated GPUs (for example, hardware decoding is not even enabled by default). Low power GPUs may cause issues like tearing, stutter, etc. The main video output uses shaders for video rendering and scaling, rather than GPU fixed function hardware. On Windows, you might want to make sure the graphics drivers are current. In some cases, ancient fallback video output methods can help (such as --vo=xv on Linux), but this use is not recommended or supported.

Downloads

For semi-official builds and third-party packages please see mpv.io/installation.

Changelog

There is no complete changelog; however, changes to the player core interface are listed in the interface changelog.

Changes to the C API are documented in the client API changelog.

The release list has a summary of most of the important changes on every release.

Changes to the default key bindings are indicated in restore-old-bindings.conf.

Compilation

Compiling with full features requires development files for several external libraries. One of the two build systems supported by mpv is required: meson or waf. Meson can be obtained from your distro or PyPI. Waf can be downloaded by using the ./bootstrap.py script. It will get the latest version of waf that was tested with mpv. Some documentation about the differences between the build systems are located in build-system-differences.

Note: Building with waf is considered deprecated and will be removed in the future.

Meson

After creating your build directory (e.g. meson setup build), you can view a list of all the build options via meson configure build. You could also just simply look at the meson_options.txt file. Logs are stored in meson-logs within your build directory.

Example:

meson setup build
meson compile -C build
meson install -C build

Waf

For a list of the available build options use ./waf configure --help. If you think you have support for some feature installed but configure fails to detect it, the file build/config.log may contain information about the reasons for the failure.

NOTE: To avoid cluttering the output with unreadable spam, --help only shows one of the two switches for each option. If the option is autodetected or enabled by default, the --disable-*** switch is printed; if the option is disabled by default, the --enable-*** switch is printed. Either way, you can use --enable-*** or --disable-** regardless of what is printed by --help.

To build the software you can use ./waf build: the result of the compilation will be located in build/mpv. You can use ./waf install to install mpv to the prefix after it is compiled.

Example:

./bootstrap.py
./waf configure
./waf
./waf install

Essential dependencies (incomplete list):

  • gcc or clang
  • X development headers (xlib, xrandr, xext, xscrnsaver, xinerama, libvdpau, libGL, GLX, EGL, xv, ...)
  • Audio output development headers (libasound/ALSA, pulseaudio)
  • FFmpeg libraries (libavutil libavcodec libavformat libswscale libavfilter and either libswresample or libavresample)
  • zlib
  • iconv (normally provided by the system libc)
  • libass (OSD, OSC, text subtitles)
  • Lua (optional, required for the OSC pseudo-GUI and youtube-dl integration)
  • libjpeg (optional, used for screenshots only)
  • uchardet (optional, for subtitle charset detection)
  • nvdec and vaapi libraries for hardware decoding on Linux (optional)

Libass dependencies (when building libass):

  • gcc or clang, yasm on x86 and x86_64
  • fribidi, freetype, fontconfig development headers (for libass)
  • harfbuzz (required for correct rendering of combining characters, particularly for correct rendering of non-English text on OSX, and Arabic/Indic scripts on any platform)

FFmpeg dependencies (when building FFmpeg):

  • gcc or clang, yasm on x86 and x86_64
  • OpenSSL or GnuTLS (have to be explicitly enabled when compiling FFmpeg)
  • libx264/libmp3lame/libfdk-aac if you want to use encoding (have to be explicitly enabled when compiling FFmpeg)
  • For native DASH playback, FFmpeg needs to be built with --enable-libxml2 (although there are security implications, and DASH support has lots of bugs).
  • AV1 decoding support requires dav1d.
  • For good nvidia support on Linux, make sure nv-codec-headers is installed and can be found by configure.

Most of the above libraries are available in suitable versions on normal Linux distributions. For ease of compiling the latest git master of everything, you may wish to use the separately available build wrapper (mpv-build) which first compiles FFmpeg libraries and libass, and then compiles the player statically linked against those.

If you want to build a Windows binary, you either have to use MSYS2 and MinGW, or cross-compile from Linux with MinGW. See Windows compilation.

Release cycle

Every other month, an arbitrary git snapshot is made, and is assigned a 0.X.0 version number. No further maintenance is done.

The goal of releases is to make Linux distributions happy. Linux distributions are also expected to apply their own patches in case of bugs and security issues.

Releases other than the latest release are unsupported and unmaintained.

See the release policy document for more information.

Bug reports

Please use the issue tracker provided by GitHub to send us bug reports or feature requests. Follow the template's instructions or the issue will likely be ignored or closed as invalid.

Using the bug tracker as place for simple questions is fine but IRC is recommended (see Contact below).

Contributing

Please read contribute.md.

For small changes you can just send us pull requests through GitHub. For bigger changes come and talk to us on IRC before you start working on them. It will make code review easier for both parties later on.

You can check the wiki or the issue tracker for ideas on what you could contribute with.

License

GPLv2 "or later" by default, LGPLv2.1 "or later" with --enable-lgpl. See details.

History

This software is based on the MPlayer project. Before mpv existed as a project, the code base was briefly developed under the mplayer2 project. For details, see the FAQ.

Contact

Most activity happens on the IRC channel and the github issue tracker.

  • GitHub issue tracker: issue tracker (report bugs here)
  • User IRC Channel: #mpv on irc.libera.chat
  • Developer IRC Channel: #mpv-devel on irc.libera.chat
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Description
🎥 Command line media player
Readme
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C 88%
Lua 5.8%
Swift 2.3%
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