This is useful for allowing the ability to have private data associated
with the object type definition structures.  This private data can be
useful for things like plugin wrappers for other languages, or providing
dynamically generated object types.

API changed:
--------------------------

void obs_output_set_audio_encoder(
		obs_output_t *output,
		obs_encoder_t *encoder);

obs_encoder_t *obs_output_get_audio_encoder(
		const obs_output_t *output);

obs_encoder_t *obs_audio_encoder_create(
		const char *id,
		const char *name,
		obs_data_t *settings);

Changed to:
--------------------------

/* 'idx' specifies the track index of the output */
void obs_output_set_audio_encoder(
		obs_output_t *output,
		obs_encoder_t *encoder,
		size_t idx);

/* 'idx' specifies the track index of the output */
obs_encoder_t *obs_output_get_audio_encoder(
		const obs_output_t *output,
		size_t idx);

/* 'mixer_idx' specifies the mixer index to capture audio from */
obs_encoder_t *obs_audio_encoder_create(
		const char *id,
		const char *name,
		obs_data_t *settings,
		size_t mixer_idx);

Overview
--------------------------
This feature allows multiple audio mixers to be used at a time.  This
capability was able to be added with surprisingly very little extra
overhead.  Audio will not be mixed unless it's assigned to a specific
mixer, and mixers will not mix unless they have an active mix
connection.

Mostly this will be useful for being able to separate out specific audio
for recording versus streaming, but will also be useful for certain
streaming services that support multiple audio streams via RTMP.

I didn't want to use a variable amount of mixers due to the desire to
reduce heap allocations, so currently I set the limit to 4 simultaneous
mixers; this number can be increased later if needed, but honestly I
feel like it's just the right number to use.

Sources:

Sources can now specify which audio mixers their audio is mixed to; this
can be a single mixer or multiple mixers at a time.  The
obs_source_set_audio_mixers function sets the audio mixer which an audio
source applies to.  For example, 0xF would mean that the source applies
to all four mixers.

Audio Encoders:

Audio encoders now must specify which specific audio mixer they use when
they encode audio data.

Outputs:

Outputs that use encoders can now support multiple audio tracks at once
if they have the OBS_OUTPUT_MULTI_TRACK capability flag set.  This is
mostly only useful for certain types of RTMP transmissions, though may
be useful for file formats that support multiple audio tracks as well
later on.

I neglected to surround some files with extern "C", so if something
written with C++ used the files it would cause function exports to not
be mangled by it correctly.

Typedef pointers are unsafe.  If you do:
typedef struct bla *bla_t;
then you cannot use it as a constant, such as: const bla_t, because
that constant will be to the pointer itself rather than to the
underlying data.  I admit this was a fundamental mistake that must
be corrected.

All typedefs that were pointer types will now have their pointers
removed from the type itself, and the pointers will be used when they
are actually used as variables/parameters/returns instead.

This does not break ABI though, which is pretty nice.

Renamed:                       To:
-------------------------------------------------------
obs_source_info::defaults       obs_source_info::get_defaults
obs_source_info::properties     obs_source_info::get_properties
obs_output_info::defaults       obs_output_info::get_defaults
obs_output_info::properties     obs_output_info::get_properties
obs_output_info::total_bytes    obs_output_info::get_total_bytes
obs_output_info::dropped_frames obs_output_info::get_dropped_frames
obs_encoder_info::defaults      obs_encoder_info::get_defaults
obs_encoder_info::properties    obs_encoder_info::get_properties
obs_encoder_info::extra_data    obs_encoder_info::get_extra_data
obs_encoder_info::sei_data      obs_encoder_info::get_sei_data
obs_encoder_info::audio_info    obs_encoder_info::get_audio_info
obs_encoder_info::video_info    obs_encoder_info::get_video_fino
obs_service_info::defaults      obs_service_info::get_defaults
obs_service_info::properties    obs_service_info::get_properties

Renamed:                    To:
-------------------------------------------------------
obs_source_info::getname    obs_source_info::get_name
obs_source_info::getwidth   obs_source_info::get_width
obs_source_info::getheight  obs_source_info::get_height
obs_output_info::getname    obs_output_info::get_name
obs_encoder_info::getname   obs_encoder_info::get_name
obs_service_info::getname   obs_service_info::get_name

Total bytes, total frames, and frames dropped.  Total frames is
generated automatically, but total bytes and total dropped frames are
returned via callbacks.

The locale parameter was a mistake, because it puts extra needless
burden upon the module developer to have to handle this variable for
each and every single callback function.  The parameter is being removed
in favor of a single centralized module callback function that
specifically updates locale information for a module only when needed.

Instead of doing this, just use macros to handle this situation.

Also, fix a minor bug in AAC encoder

Improve the properties API so that it can actually respond somewhat to
user input.  Maybe later this might be further improved or replaced with
something script-based.

When creating a property, you can now add a callback to that property
that notifies when the property has been changed in the user interface.
Return true if you want the properties to be refreshed, or false if not.
Though now that I think about it I doubt there would ever be a case
where you would have this callback and *not* refresh the properties.

Regardless, this allows functions to change the values of properties or
settings, or enable/disable/hide other property controls from view
dynamically.

 - Add start/stop code to obs-output module

 - Use a circular buffer for the buffered encoder packets instead of a
   dynamic array

 - Add pthreads.lib as a dependency to obs-output module on windows in
   visual studio project files

 - Fix an windows export bug for avc parsing functions on windows.
   Also, rename those functions to be more consistent with each other.

 - Make outputs use a single function for encoded data rather than
   multiple functions

 - Add the ability to make 'text' properties be passworded

 - obs-outputs module:  Add preliminary code to send out data, and add
   an FLV muxer.  This time we don't really need to build the packets
   ourselves, we can just use the FLV muxer and send it directly to
   RTMP_Write and it should automatically parse the entire stream for us
   without us having to do much manual code at all.  We'll see how it
   goes.

 - libobs:  Add AVC NAL packet parsing code

 - libobs/media-io:  Add quick helper functions for audio/video to get
   the width/height/fps/samplerate/etc rather than having to query the
   info structures each time.

 - libobs (obs-output.c):  Change 'connect' signal to 'start' and 'stop'
   signals.  'start' now specifies an error code rather than whether it
   simply failed, that way the client can actually know *why* a failure
   occurred.  Added those error codes to obs-defs.h.

 - libobs:  Add a few functions to duplicate/free encoder packets

 - Make it so that encoders can be assigned to outputs.  If an encoder
   is destroyed, it will automatically remove itself from that output.
   I specifically didn't want to do reference counting because it leaves
   too much potential for unchecked references and it just felt like it
   would be more trouble than it's worth.

 - Add a 'flags' value to the output definition structure.  This lets
   the output specify if it uses video/audio, and whether the output is
   meant to be used with OBS encoders or not.

 - Remove boilerplate code for outputs.  This makes it easier to program
   outputs.  The boilerplate code involved before was mostly just
   involving connecting to the audio/video data streams directly in each
   output plugin.

   Instead of doing that, simply add plugin callback functions for
   receiving video/audio (either encoded or non-encoded, whichever it's
   set to use), and then call obs_output_begin_data_capture and
   obs_output_end_data_capture to automatically handle setting up
   connections to raw or encoded video/audio streams for the plugin.

 - Remove 'active' function from output callbacks, as it's no longer
   really needed now that the libobs output context automatically knows
   when the output is active or not.

 - Make it so that an encoder cannot be destroyed until all data
   connections to the encoder have been removed.

 - Change the 'start' and 'stop' functions in the encoder interface to
   just an 'initialize' callback, which initializes the encoder.

 - Make it so that the encoder must be initialized first before the data
   stream can be started.  The reason why initialization was separated
   from starting the encoder stream was because we need to be able to
   check that the settings used with the encoder *can* be used first.

   This problem was especially annoying if you had both video/audio
   encoding.  Before, you'd have to check the return value from
   obs_encoder_start, and if that second encoder fails, then you
   basically had to stop the first encoder again, making for
   unnecessary boilerplate code whenever starting up two encoders.

 - Implement a means of obtaining default settings for an
   input/output/encoder.  obs_source_defaults for example will return
   the default settings for a particular source type.

 - Because C++ doesn't have designated initializers, use functions in
   the WASAPI plugin to register the sources instead.

The API used to be designed in such a way to where it would expect
exports for each individual source/output/encoder/etc.  You would export
functions for each and it would automatically load those functions based
on a specific naming scheme from the module.

The idea behind this was that I wanted to limit the usage of structures
in the API so only functions could be used.  It was an interesting idea
in theory, but this idea turned out to be flawed in a number of ways:

 1.) Requiring exports to create sources/outputs/encoders/etc meant that
     you could not create them by any other means, which meant that
     things like faruton's .net plugin would become difficult.

 2.) Export function declarations could not be checked, therefore if you
     created a function with the wrong parameters and parameter types,
     the compiler wouldn't know how to check for that.

 3.) Required overly complex load functions in libobs just to handle it.
     It makes much more sense to just have a load function that you call
     manually.  Complexity is the bane of all good programs.

 4.) It required that you have functions of specific names, which looked
     and felt somewhat unsightly.

So, to fix these issues, I replaced it with a more commonly used API
scheme, seen commonly in places like kernels and typical C libraries
with abstraction.  You simply create a structure that contains the
callback definitions, and you pass it to a function to register that
definition (such as obs_register_source), which you call in the
obs_module_load of the module.

It will also automatically check the structure size and ensure that it
only loads the required values if the structure happened to add new
values in an API change.

The "main" source file for each module must include obs-module.h, and
must use OBS_DECLARE_MODULE() within that source file.

Also, started writing some doxygen documentation in to the main library
headers.  Will add more detailed documentation as I go.

- Add property list callbacks to sources/outputs/encoders so that if
  necessary user interface can be automatically generated or perhaps a
  property list widget can be used for them.

- Change some of the property API names.  obs_property_list_t felt a bit
  awkward when actually using it, so I just renamed it to
  obs_properties_t.

- Removed the getdata/setdata nad getparam/setparam functions from
  sources/services, they will be superseded by the dynamic procedure
  call API.

Add a fairly easy to use settings interface that can be passed to
plugins, and replaced the old character string system that was being
used before.  The new data interface allows for an easier method of
getting/altering settings for plugins, and is built to be serializable
to/from JSON.

Also, removed another wxFormBuilder file that was no longer in use.

- Added some code for FFmpeg output that I'm still playing around with.
  Right now I'm just trying to get it to output to file and try to
  understand the FFmpeg/libav APIs.  Hopefully in the future this plugin
  can be used for any sort of output to FFmpeg.

- Fixed a cast warning in audio-io.c with size_t -> uint32_t

- Renamed the 'video_info' and 'audio_info' structures to
  'video_conver_info' and 'audio_convert_info' to better represent their
  actual purpose, and to avoid confusion with 'audio_output_info' and
  'video_output_info' structures.

- Removed a few macros from obs-def.h that were at one point going to be
  used but no longer going to be used (at least for now)

Changed the comments to properly reflect the new callbacks, as I had
forgotten to update the comments for them both.

Also, changed "setbitrate" and "request_keyframe" return values to be
boolean.

- First, I redid the output interface for libobs.  I feel like it's
  going in a pretty good direction in terms of design.

  Right now, the design is so that outputs and encoders are separate.
  One or more outputs can connect to a specific encoder to receive its
  data, or the output can connect directly to raw data from libobs
  output itself, if the output doesn't want to use a designated encoder.
  Data is received via callbacks set when you connect to the encoder or
  raw output.  Multiple outputs can receive the data from a single
  encoder context if need be (such as for streaming to multiple channels
  at once, and/or recording with the same data).

  When an encoder is first connected to, it will connect to raw output,
  and start encoding.  Additional connections will receive that same
  data being encoded as well after that.  When the last encoder has
  disconnected, it will stop encoding.  If for some reason the encoder
  needs to stop, it will use the callback with NULL to signal that
  encoding has stopped.  Some of these things may be subject to change
  in the future, though it feels pretty good with this design so far.
  Will have to see how well it works out in practice versus theory.

- Second, Started adding preliminary RTMP/x264 output plugin code.

  To speed things up, I might just make a direct raw->FFmpeg output to
  create a quick output plugin that we can start using for testing all
  the subsystems.

With the permission of my fellow contributors, I'm switching obs-studio back to GPL v2+ to prevent issues between this project and the original OBS project, and for personal reasons to avoid legal ambiguity (not political reasons, I admittedly would prefer GPL v3+)

added support for jansson, added new output files, made some adjustments to the API, fixed a UI subclass issue