Don't randomly change backgrounds when all we have is one

image; we end up looping movies.

stepmania/src/Background.cpp

@@ -301,9 +301,16 @@ void Background::LoadFromSong( Song* pSong )
 		// start off showing the static song background
 		m_aBGSegments.Add( BGSegment(-10000,0) );
 
-		// change BG every 4 bars
+		/* If we have only 2, only generate a single animation segment for for the
+		 * whole song.  Otherwise, if it's a movie., it'll loop every four bars; we
+		 * want it to play continuously. */
 		const float fFirstBeat = m_BackgroundMode==MODE_MOVIE_BG ? 0 : pSong->m_fFirstBeat;
 		const float fLastBeat = pSong->m_fLastBeat;
+
+		if( m_BackgroundAnimations.GetSize() == 2) {
+			m_aBGSegments.Add( BGSegment(fFirstBeat,1) );
+		} else {
+			// change BG every 4 bars
 			for( float f=fFirstBeat; f<fLastBeat; f+=16 )
 			{
 				int index;
@@ -331,14 +338,13 @@ void Background::LoadFromSong( Song* pSong )
 					index = 1 + int(bpmseg.m_fBPM)%(m_BackgroundAnimations.GetSize()-1);
 				m_aBGSegments.Add( BGSegment(bpmseg.m_fStartBeat,index) );
 			}
+		}
 
 		// end showing the static song background
 		m_aBGSegments.Add( BGSegment(pSong->m_fLastBeat,0) );
 		
 		// sort segments
 		SortBGSegmentArray( m_aBGSegments );
-
-
 	}
 
 	for( int i=0; i<m_BackgroundAnimations.GetSize(); i++ )