release version 0.4.1

- macOS: fix glx weak link
- support ubuntu >= 14.04
- load vaapi dynamically
- improve vaapi host map, control via env var VAIMAGE_DERIVE, VAIMAGE_FORMAT
- fix many playback loop bugs when more tracks are enabled
- fix too many packets buffered when decoding the 1st frame
- MFT: disable low latency to fix frames out of order
- subtitle support WIP.
  - decode embedded subtitle tracks via avcodec
  - decode loop and thread
- FFmpeg
  - versioned dso is preferred
  - reload ffmpeg symbols if dso is changed by SetGlobalOption()
  - log level is controlled by SetGlobalOption("ffmpeg.loglevel", val), val can be "quiet", "panic", "fatal", "error", "warning", "info", "verbose", "debug", "trace"

README.md

@@ -19,7 +19,7 @@ FFmpeg modules can be specified via environment var AVUTIL_LIB, AVCODEC_LIB, AVF
 
 If ffmpeg any module is not set, it's searched in the following order
 - current module dir > framework dir(apple) > system default search dir
-- single ffmpeg library > ffmpeg modules w/ version > ffmpeg modules w/o version
+- single ffmpeg library w/ version > single ffmpeg library w/o version > ffmpeg modules w/ version > ffmpeg modules w/o version
 
 ## MDK OpenGL v.s. MPV OpenGL CB
 - No additional initialization, simply call renderVideo()
@@ -40,6 +40,7 @@ If ffmpeg any module is not set, it's searched in the following order
 - Subtitle decoder and renderer
 - Vulkan
 - D3D
+- Metal
 - V4L2 codecs + 0-copy rendering(Raspberry pi)
 
 ## Open Source Modules and Examples