CoreAudio: capture 128 frames

Capture only 128 frames at once (implicit value was 512).

+ param to allow user to set it manually

src/host.cpp

@@ -395,6 +395,8 @@ bool register_mainloop(mainloop_t m, void *u)
 // some common parameters used within multiple modules
 ADD_TO_PARAM(audio_buffer_len, "audio-buffer-len", "* audio-buffer-len=<ms>\n"
                 "  Sets length of software audio playback buffer (in ms, ALSA/Coreaudio/Portaudio)\n");
+ADD_TO_PARAM(audio_cap_frames, "audio-cap-frames", "* audio-cap-frames=<f>\n"
+                "  Sets number of audio frames captured at once (CoreAudio)\n");
 ADD_TO_PARAM(low_latency_audio, "low-latency-audio", "* low-latency-audio\n"
                 "  Try to reduce audio latency at the expense of worse reliability\n");
 ADD_TO_PARAM(window_title, "window-title", "* window-title=<title>\n"