* add config and GUI support for internal player back end switching;
* make FFmpeg player disabling option consistent with other similar
qmake options by using CONFIG;
* add a new qmake option that disables Qt Multimedia player. This is
useful for GNU/Linux distributions where Qt WebKit and Qt Multimedia
packages depend on different GStreamer versions and don't work
correctly when combined in one application.
The existing FFmpeg+libao internal player back end has a relatively
low-level implementation, which is difficult to understand and improve.
There are at least 3 open internal player issues:
1) many GNU/Linux users have to edit their libao configuration file to
make Goldendict's internal player work (issue #412);
2) libao's pulseaudio plugin does not support 32-bit audio, which
means that many MediaWiki pronunciations don't work with the most
popular GNU/Linux audio driver (issue #949);
3) Ffmpeg::DecoderContext uses deprecated FFmpeg APIs, which causes
compiler warnings and means that this internal player back end
may not compile with a future FFmpeg library version (issue #978).
The Qt Multimedia back end implementation uses the highest-level
Qt audio API and is very simple.
This new back end works flawlessly on my GNU/Linux machine.
I'm not making it the default back end because I don't know how well
it will work on other platforms with different configurations.
External and internal audio players work similarly now. Fixes #950.
* inherit a new ExternalAudioPlayer class from AudioPlayerInterface;
* use an existing ExternalViewer class to implement ExternalAudioPlayer;
* take (const char *, int) instead of std::vector<char> in
ExternalViewer constructor to fit into AudioPlayerInterface;
* extend ExternalViewer API to let ExternalAudioPlayer stop superseded
audio player processes;
* make AudioPlayerInterface::play() return an error message string to
allow reporting immediate failures from derived classes;
* Document AudioPlayerInterface API;
* Document AudioPlayerFactory::player();
* use the common audio interface exclusively in ArticleView.
* add a new interface class AudioPlayerInterface;
* inherit a new proxy class Ffmpeg::AudioPlayer from it;
* partially switch ArlticleView to using the interface;
* expose MainWindow's AudioPlayerInterface instance to all ArticleView
instances;
* add a new AudioPlayerFactory class responsible for creating instances
of concrete classes derived from AudioPlayerInterface depending on
relevant Config::Preferences values;
* increase minimum supported Qt version from 4.5 to 4.6 in README
in order to use QScopedPointer introduced in Qt 4.6.
