avformat/avformat: Move AVOutputFormat internals out of public header

This commit does for AVOutputFormat what commit
20f9727018 did for AVCodec:
It adds a new type FFOutputFormat, moves all the internals
of AVOutputFormat to it and adds a now reduced AVOutputFormat
as first member.

This does not affect/improve extensibility of both public
or private fields for muxers (it is still a mess due to lavd).

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavformat/wvenc.c

@@ -24,6 +24,7 @@
 
 #include "apetag.h"
 #include "avformat.h"
+#include "mux.h"
 #include "wv.h"
 
 typedef struct WvMuxContext {
@@ -76,16 +77,16 @@ static av_cold int wv_write_trailer(AVFormatContext *ctx)
     return 0;
 }
 
-const AVOutputFormat ff_wv_muxer = {
-    .name              = "wv",
-    .long_name         = NULL_IF_CONFIG_SMALL("raw WavPack"),
-    .mime_type         = "audio/x-wavpack",
-    .extensions        = "wv",
+const FFOutputFormat ff_wv_muxer = {
+    .p.name            = "wv",
+    .p.long_name       = NULL_IF_CONFIG_SMALL("raw WavPack"),
+    .p.mime_type       = "audio/x-wavpack",
+    .p.extensions      = "wv",
     .priv_data_size    = sizeof(WvMuxContext),
-    .audio_codec       = AV_CODEC_ID_WAVPACK,
-    .video_codec       = AV_CODEC_ID_NONE,
+    .p.audio_codec     = AV_CODEC_ID_WAVPACK,
+    .p.video_codec     = AV_CODEC_ID_NONE,
     .init              = wv_init,
     .write_packet      = wv_write_packet,
     .write_trailer     = wv_write_trailer,
-    .flags             = AVFMT_NOTIMESTAMPS,
+    .p.flags           = AVFMT_NOTIMESTAMPS,
 };