Fix build against FFmpeg 8 (libavcodec 62 / libswscale).

- The SWS_* scaler flags became an enum (previously macros), so SWS_BICUBIC now
  lives inside StepMania's "avcodec" namespace wrapper and must be qualified.
- avcodec_close() was removed; use avcodec_free_context() (closes and frees) for
  teardown, and free+realloc the context to reset it before reopening.

All changes are guarded by LIBAVCODEC_VERSION_MAJOR so older FFmpeg still builds.
--- a/src/arch/MovieTexture/MovieTexture_FFMpeg.h
+++ b/src/arch/MovieTexture/MovieTexture_FFMpeg.h
@@ -33,7 +33,13 @@
 };
 
 #define STEPMANIA_FFMPEG_BUFFER_SIZE 4096
+#ifdef SWS_BICUBIC
 static const int sws_flags = SWS_BICUBIC; // XXX: Reasonable default?
+#else
+// FFmpeg 8 turned the SWS_* flags from macros into an enum, so they now live
+// inside this file's "avcodec" namespace wrapper and must be qualified.
+static const int sws_flags = avcodec::SWS_BICUBIC;
+#endif
 
 class MovieTexture_FFMpeg: public MovieTexture_Generic
 {
--- a/src/arch/MovieTexture/MovieTexture_FFMpeg.cpp
+++ b/src/arch/MovieTexture/MovieTexture_FFMpeg.cpp
@@ -514,8 +514,19 @@
 	m_fLastFrame = 0;
 
 	ASSERT( m_pStream != nullptr );
+#if LIBAVCODEC_VERSION_MAJOR >= 58
+	// avcodec_close() was removed in FFmpeg 8.  Reset the context by freeing
+	// and reallocating it from the stream parameters before (re)opening.
+	if( m_pStreamCodec->codec )
+	{
+		avcodec::avcodec_free_context( &m_pStreamCodec );
+		m_pStreamCodec = avcodec::avcodec_alloc_context3( nullptr );
+		avcodec::avcodec_parameters_to_context( m_pStreamCodec, m_pStream->codecpar );
+	}
+#else
 	if( m_pStreamCodec->codec )
 		avcodec::avcodec_close( m_pStreamCodec );
+#endif
 
 	const avcodec::AVCodec *pCodec = avcodec::avcodec_find_decoder( m_pStreamCodec->codec_id );
 	if( pCodec == nullptr )
@@ -542,11 +553,21 @@
 
 void MovieDecoder_FFMpeg::Close()
 {
+#if LIBAVCODEC_VERSION_MAJOR >= 58
+	// avcodec_close() was removed in FFmpeg 8; avcodec_free_context() both
+	// closes and frees the context (and NULLs it, so the later cleanup skips).
+	if( m_pStream && m_pStreamCodec && m_pStreamCodec->codec )
+	{
+		avcodec::avcodec_free_context( &m_pStreamCodec );
+		m_pStream = nullptr;
+	}
+#else
 	if( m_pStream && m_pStreamCodec->codec )
 	{
 		avcodec::avcodec_close( m_pStreamCodec );
 		m_pStream = nullptr;
 	}
+#endif
 
 	if( m_fctx )
 	{