avformatdecoder.cpp: remove '#include "libavformat/internal.h"'

refs: #428

ff_read_frame_flush() is an internal FFmpeg function.

However, in libavformat/utils.c:
int avformat_flush(AVFormatContext *s)
{
    ff_read_frame_flush(s);
    return 0;
}

avformat_flush() is exactly identical and is a public function,
so use it instead.

StreamHasRequiredParameters():
The audio check requiring the internal struct to be defined was disabled.
This should have no effect since these checks are *all* already done via
avformat_find_stream_info() in FindStreamInfo(), which should return < 0
if these checks fail.

This copy of an internal FFmpeg function feels unnecessary and like a bad idea
since FFmpeg already checks this itself.

mythtv/libs/libmythtv/decoders/avformatdecoder.cpp

@@ -17,7 +17,6 @@ extern "C" {
 #include "libavcodec/avcodec.h"
 #include "libavformat/avformat.h"
 #include "libavformat/avio.h"
-#include "libavformat/internal.h"
 #include "libswscale/swscale.h"
 #include "libavutil/stereo3d.h"
 #include "libavutil/imgutils.h"
@@ -200,6 +199,7 @@ int  get_avf_buffer_dxva2(struct AVCodecContext *c, AVFrame *pic, int flags);
     return false;                                   \
 } while (false)
 
+// This is a slightly modified static int has_codec_parameters() from libavformat/utils.c
 static bool StreamHasRequiredParameters(AVCodecContext *Context, AVStream *Stream)
 {
     switch (Stream->codecpar->codec_type)
@@ -744,7 +744,7 @@ void AvFormatDecoder::SeekReset(long long newKey, uint skipFrames,
         m_ptsDetected = false;
         m_reorderedPtsDetected = false;
 
-        ff_read_frame_flush(m_ic);
+        avformat_flush(m_ic);
 
         // Only reset the internal state if we're using our seeking,
         // not when using libavformat's seeking