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This file intends to give a big picture of how mpv is structured.
player/*.c:
Essentially makes up the player applications, including the main() function
and the playback loop.
Generally, it accesses all other subsystems, initializes them, and pushes
data between them during playback.
The structure is as follows (as of commit e13c05366557cb):
* main():
* basic initializations (e.g. init_libav() and more)
* pre-parse command line (verbosity level, config file locations)
* load config files (parse_cfgfiles())
* parse command line, add files from the command line to playlist
(m_config_parse_mp_command_line())
* check help options etc. (call handle_help_options()), possibly exit
* call play_files() function that works down the playlist:
* run idle loop (idle_loop()), until there are files in the
playlist or an exit command was given (slave mode only)
* actually load and play a file in play_current_file():
* run all the dozens of functions to load the file and
initialize playback
* run a small loop that does normal playback, until the file is
done or a slave command terminates playback
(on each iteration, run_playloop() is called, which is rather
big and complicated - it decodes some audio and video on
each frame, waits for input, etc.)
* uninitialize playback
* determine next entry on the playlist to play
* loop, or exit if no next file or quit is requested
(see enum stop_play_reason)
* call exit_player_with_rc()
Things worth saying about the playback core:
- the currently played tracks are in sh_video and sh_audio
- the timeline stuff is used only with MKV ordered chapters (and some other
minor features: cue, edl)
- most state is in MPContext (mp_core.h), which is not available to the
subsystems
- the other subsystems rarely call back into the frontend, and the frontend
polls them instead (probably a good thing)
I like to call the player/*.c files the "frontend".
talloc.h & talloc.c:
Hierarchical memory manager copied from Samba. It's like a malloc() with
more features. Most importantly, each talloc allocation can have a parent,
and if the parent is free'd, all children will be free'd as well. The
parent is an arbitrary talloc allocation. It's either set by the allocation
call by passing a talloc parent, usually as first argument to the allocation
function. It can also be set or reset later by other calls (at least
talloc_steal()). A talloc allocation that is used as parent is often called
a talloc context.
Lots of code still uses malloc() proper, and you should be careful what
type of allocation you're dealing with when returning or free'ing an
allocation. (Needless to say, talloc_free() and free() are completely
different things.)
The copy in mpv has been modified to abort on OOM conditions. An
allocation call will never return NULL.
One very useful feature of talloc is fast tracking of memory leaks. ("Fast"
as in it doesn't require valgrind.) You can enable it by passing the option
--leak-report as first parameter, or better, setting the
MPV_LEAK_REPORT environment variable to "1":
export MPV_LEAK_REPORT=1
This will list all unfree'd allocations on exit.
Documentation can be found here:
http://git.samba.org/?p=samba.git;a=blob;f=lib/talloc/talloc.h;hb=HEAD
Note: unlike tcmalloc, jemalloc, etc., talloc() is not actually a malloc
replacement. It works on top of system malloc and provides additional
features that are supposed to make memory management easier.
Warning: actually, we're not using talloc anymore. talloc in mpv has been
replaced by a custom re-implementation (TA in ta/). It provides
some talloc emulation (just the parts needed by mpv). We will get
rid of the talloc emulation later and use TA natively.
(See ta/README for details.)
player/command.c:
This contains the implementation for slave commands and properties.
Properties are essentially dynamic variables changed by certain commands.
This is basically responsible for all user commands, like initiating
seeking, switching tracks, etc. It calls into other player/*.c files,
where most of the work is done, but also calls other parts of mpv.
player/core.h:
Data structures and function prototypes for most of player/*.c. They are
usually not accessed by other parts of mpv for the sake of modularization.
Note that there are lots of global variables floating around everywhere
else. This is an ongoing transition, and eventually there should be no
global variables anymore.
options/options.h, options/options.c
options.h contains the global option struct MPOpts. The option declarations
(option names, types, and MPOpts offsets for the option parser) are in
options.c. Most default values for options and MPOpts are in
mp_default_opts at the end of options.c.
MPOpts is unfortunarely quite monolithic, and virtually accessed by
everything.But some components (like video outputs and video filters) have
their own sub-option tables separate from MPOpts.
The actual option parser is spread over m_option.c, m_config.c, and
parser-mpcmd.c, and uses the option table in options.c.
input/input.c:
This translates keyboard input comming from libvo and other sources (such
as remote control devices like Apple IR or slave mode commands) to the
key bindings listed in the user's (or the builtin) input.conf and turns
them into items of type struct mp_cmd. These commands are queued, and read
by playloop.c. They get pushed with run_command() to command.c.
Note that keyboard input and slave mode input are essentially the same
things. Just looking at input.conf should make this clear. (The other
direction of slave mode communication, mpv to application, consists of
random mp_msg() calls all over the code in all parts of the player.)
common/msg.h:
All terminal output should go through mp_msg().
stream/*:
File input is implemented here. stream.h/.c provides a simple stream based
interface (like reading a number of bytes at a given offset). mpv can
also play from http streams and such, which is implemented here.
E.g. if mpv sees "http://something" on the command line, it will pick
stream_lavf.c based on the prefix, and pass the rest of the filename to it.
Some stream inputs are quite special: stream_dvd.c turns DVDs into mpeg
streams (DVDs are actually a bunch of vob files etc. on a filesystem),
stream_tv.c provides TV input including channel switching.
Some stream inputs are just there to invoke special demuxers, like
stream_mf.c. (Basically to make the prefix "mf://" do something special.)
cache.c is a caching wrapper around streams implementations, needed for
smooth network playback.
demux/:
Demuxers split data streams into audio/video/sub streams, which in turn
are split in packets. Packets (see demux_packet.h) are mostly byte chunks
tagged with a playback time (PTS). These packets are passed to the decoders.
Most demuxers have been removed from this fork, and the only important and
"actual" demuxers left are demux_mkv.c and demux_lavf.c (uses libavformat).
There are some pseudo demuxers like demux_cue.c, which exist only to invoke
other frontend code (tl_cue.c in this case).
The main interface is in demux.h. The stream headers are in stheader.h.
There is a stream header for each audio/video/sub stream, and each of them
holds codec information about the stream and other information.
video/:
This contains several things related to audio/video decoding, as well as
video filters.
mp_image.h and img_format.h define how mpv stores decoded video frames
internally.
video/decode/:
vd_*.c are video decoders. (There's only vd_lavc.c left.) dec_video.c/vd.c
handle most of connecting the frontend with the actual decoder.
video/filter/:
vf_*.c and vf.c form the video filter chain. They are fed by the video
decoder, and output the filtered images to the VOs though vf_vo.c. By
default, no video filters (except vf_vo) are used. vf_scale is automatically
inserted if the video output can't handle the video format used by the
decoder.
video/out/:
Video output. They also create GUI windows and handle user input. In most
cases, the windowing code is shared among VOs, like x11_common.c for X11 and
w32_common.c for Windows. The VOs stand between frontend and windowing code.
vo_opengl can pick a windowing system at runtime, e.g. the same binary can
provide both X11 and Cocoa support on OSX.
VOs can be reconfigured at runtime. A config() call can change the video
resolution and format, without destroying the window.
vo_vdpau and vo_opengl should be taken as reference.
audio/:
format.h/format.c define the uncompressed audio formats. (As well as some
compressed formats used for spdif.)
audio/decode/:
ad_*.c and dec_audio.c/ad.c handle audio decoding. ad_lavc.c is the
decoder using ffmpeg. ad_spdif.c is not really a decoder, but is used for
compressed audio passthrough.
audio/filter/:
Audio filter chain. af_lavrresample is inserted if any form of conversion
between audio formats is needed. (af_convert24.c and af_convertsignendian.c
are also used for some formats not directly supported by FFmpeg.)
audio/out/:
Audio outputs.
Unlike VOs, AOs can't be reconfigured on a format change. Without
--gapless-audio, even playing a new file will close and re-open the audio
device.
Note that mpv synchronizes the video to the audio. That's the reason
why buggy audio drivers can have a bad influence on playback quality.
sub/:
Contains subtitle and OSD rendering.
sub.c/.h is actually the OSD code. It queries dec_sub.c to retrieve
decoded/rendered subtitles. osd_libass.c is the actual implementation of
the OSD text renderer (which uses libass, and takes care of all the tricky
fontconfig/freetype API usage and text layouting).
Subtitle loading is now in demux/ instead. demux_libass.c wraps loading
.ass subtitles via libass. demux_lavf.c loads most subtitle types via
FFmpeg. demux_subreader.c is the old MPlayer code. It's used as last
fallback, or to handle some text subtitle types on Libav. (It also can
load UTF-16 encoded subtitles without requiring the use of -sub-codepage.)
demux_subreader.c should eventually go away (maybe).
The subtitles are passed to dec_sub.c and the subtitle decoders in sd_*.c
as they are demuxed. All text subtitles are rendered by sd_ass.c. If text
subtitles are not in the ASS format, subtitle converters are inserted, for
example sd_srt.c, which is used to convert SRT->ASS. sd_srt.c is also used
as general converter for text->ASS (to prevent interpretation of text as
ASS tags).
Text subtitles can be preloaded, in which case they are read fully as soon
as the subtitle is selected, and then effectively stored in an ASS_Track.
It's used for external text subtitles, and required to make codepage
detection as well as timing postprocessing work. (Timing postprocessing
removes tiny gaps or overlaps between subtitle events.)
player/timeline/:
A timeline is the abstraction used by loadfile.c to combine several files
into one seemingly linear video. It's mainly used for ordered chapters
playback. The high level code to find and load other files containing the
segments for playing an ordered chapters file is in tl_matroska.c.
etc/:
The file input.conf is actually integrated into the mpv binary by the
build system. It contains the default keybindings.
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