Add planar audio support, improve test output

- Add planar audio support.  FFmpeg and libav use planar audio for many
  encoders, so it was somewhat necessary to add support in libobs
  itself.

- Improve/adjust FFmpeg test output plugin.  The exports were somewhat
  messed up (making me rethink how exports should be done).  Not yet
  functional; it handles video properly, but it still does not handle
  audio properly.

- Improve planar video code.  The planar video code was not properly
  accounting for row sizes for each plane.  Specifying row sizes for
  each plane has now been added.  This will also make it more compatible
  with FFmpeg/libav.

- Fixed a bug where callbacks wouldn't create properly in audio-io and
  video-io code.

- Implement 'blogva' function to allow for va_list usage with libobs
  logging.

plugins/obs-ffmpeg/obs-ffmpeg-output.h

@@ -18,6 +18,7 @@
 #pragma once
 
 #include <util/c99defs.h>
+#include <media-io/audio-io.h>
 #include <media-io/video-io.h>
 
 #include <libavformat/avformat.h>
@@ -31,12 +32,13 @@ struct ffmpeg_data {
 	AVFormatContext    *output;
 	struct SwsContext  *swscale;
 
-	AVFrame            *vframe;
-	AVPicture          src_picture;
 	AVPicture          dst_picture;
+	AVFrame            *vframe;
+	int                total_frames;
 
+	uint8_t            *samples[MAX_AUDIO_PLANES];
 	AVFrame            *aframe;
-	uint8_t            **samples;
+	int                total_samples;
 
 	bool               initialized;
 };
@@ -49,12 +51,12 @@ struct ffmpeg_output {
 
 EXPORT const char *ffmpeg_output_getname(const char *locale);
 
-EXPORT struct ffmpeg_output *ffmpeg_output_create(obs_data_t settings,
+EXPORT struct ffmpeg_output *ffmpeg_output_create(const char *settings,
 		obs_output_t output);
 EXPORT void ffmpeg_output_destroy(struct ffmpeg_output *data);
 
 EXPORT void ffmpeg_output_update(struct ffmpeg_output *data,
-		obs_data_t settings);
+		const char *settings);
 
 EXPORT bool ffmpeg_output_start(struct ffmpeg_output *data);
 EXPORT void ffmpeg_output_stop(struct ffmpeg_output *data);