obs-ffmpeg: Fix race and deprecation warnings

Attempt to simply shutdown sequence to avoid race between vidoe and
write threads. Can no longer join on write thread from write thread.

Also use codecpar instead of deprecated codec member.

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

@@ -30,9 +30,15 @@ struct ffmpeg_cfg {
 	int height;
 };
 
+struct ffmpeg_audio_info {
+	AVStream *stream;
+	AVCodecContext *ctx;
+};
+
 struct ffmpeg_data {
 	AVStream *video;
-	AVStream **audio_streams;
+	AVCodecContext *video_ctx;
+	struct ffmpeg_audio_info *audio_infos;
 	AVCodec *acodec;
 	AVCodec *vcodec;
 	AVFormatContext *output;