Courtesy of Shaul Kedem:

Option to play sequence strips (Movie, Image, Scene) in reverse.
New toggle in the NKEY buttons for sequence strips.

Thanks Shaul!

source/blender/makesdna/DNA_sequence_types.h

@@ -82,7 +82,7 @@ typedef struct PluginSeq {
 	void (*callback)(void);
 } PluginSeq;
 
-
+/* The sequence structure is the basic struct used by any strip. each of the strips uses a different sequence structure.*/
 /* WATCH IT: first part identical to ID (for use in ipo's) */
 
 typedef struct Sequence {
@@ -91,14 +91,14 @@ typedef struct Sequence {
 	void *lib;
 	char name[24];
 
-	short flag, type;
+	short flag, type;			/*flags bitmap (see below) and the type of sequence*/
 	int len;
 	int start, startofs, endofs;
 	int startstill, endstill;
 	int machine, depth;
-	int startdisp, enddisp;
+	int startdisp, enddisp;		/*starting and ending points in the sequence*/
 	float mul, handsize;
-	int sfra;
+	int sfra;				/* starting frame according to the timeline of the scene */
 
 	Strip *strip;
 	StripElem *curelem;
@@ -164,8 +164,9 @@ typedef struct GlowVars {
 #define SEQ_FILTERY		16
 #define SEQ_MUTE		32
 #define SEQ_MAKE_PREMUL	64
+#define SEQ_REVERSE_FRAMES	128
 
-/* seq->type WATCH IT: BIT 3!!! */
+/* seq->type WATCH IT: SEQ_EFFECT BIT is used to determine if this is an effect strip!!! */
 #define SEQ_IMAGE		0
 #define SEQ_META		1
 #define SEQ_SCENE		2

source/blender/src/drawseq.c

@@ -670,6 +670,7 @@ static void seq_panel_properties(short cntrl)	// SEQ_HANDLER_PROPERTIES
 		uiDefButBitS(block, TOG, SEQ_MAKE_PREMUL, SEQ_BUT_RELOAD, "Convert to Premul", 10,90,150,19, &last_seq->flag, 0.0, 21.0, 100, 0, "Converts RGB values to become premultiplied with Alpha");
 		uiDefButBitS(block, TOG, SEQ_FILTERY, SEQ_BUT_RELOAD, "FilterY",	10,70,150,19, &last_seq->flag, 0.0, 21.0, 100, 0, "For video movies to remove fields");
 		uiDefButF(block, NUM, SEQ_BUT_RELOAD, "Mul:",			10,50,150,19, &last_seq->mul, 0.001, 5.0, 100, 0, "Multiply colors");
+		uiDefButS(block, TOG|BIT|7, SEQ_BUT_RELOAD, "Reverse Frames", 10,30,150,19, &last_seq->flag, 0.0, 21.0, 100, 0, "Reverse frame order");
 	}
 	else if(last_seq->type==SEQ_META) {
 
@@ -681,7 +682,7 @@ static void seq_panel_properties(short cntrl)	// SEQ_HANDLER_PROPERTIES
 
 		uiDefBut(block, LABEL, 0, "Type: Scene", 10,140,150,20, 0, 0, 0, 0, 0, "");
 		uiDefBut(block, TEX, B_NOP, "Name: ", 10,120,150,19, last_seq->name+2, 0.0, 21.0, 100, 0, "");
-
+		uiDefButS(block, TOG|BIT|7, SEQ_BUT_RELOAD, "Reverse Frames", 10,90,150,19, &last_seq->flag, 0.0, 21.0, 100, 0, "Reverse frame order");
 	}
 	else if(last_seq->type==SEQ_MOVIE) {
 
@@ -694,6 +695,9 @@ static void seq_panel_properties(short cntrl)	// SEQ_HANDLER_PROPERTIES
 		uiDefButBitS(block, TOG, SEQ_FILTERY, SEQ_BUT_RELOAD, "FilterY ",	10,70,150,19, &last_seq->flag, 0.0, 21.0, 100, 0, "For video movies to remove fields");
 		uiDefButF(block, NUM, SEQ_BUT_RELOAD, "Mul:",			10,50,150,19, &last_seq->mul, 0.001, 5.0, 100, 0, "Multiply colors");
 		
+		uiDefButS(block, TOG|BIT|7, SEQ_BUT_RELOAD, "Reverse Frames", 10,30,150,19, &last_seq->flag, 0.0, 21.0, 100, 0, "Reverse frame order");
+
+
 	}
 	else if(last_seq->type==SEQ_SOUND) {
 

source/blender/src/sequence.c

@@ -1710,16 +1710,25 @@ StripElem *give_stripelem(Sequence *seq, int cfra)
 	if(se==0) return 0;
 	if(seq->startdisp >cfra || seq->enddisp <= cfra) return 0;
 
+	if(seq->flag&SEQ_REVERSE_FRAMES)	{	
+		/*reverse frame in this sequence */
+		if(cfra <= seq->start) nr= seq->len-1;
+		else if(cfra >= seq->start+seq->len-1) nr= 0;
+		else nr= (seq->start + seq->len) - cfra;
+	} else {
 	if(cfra <= seq->start) nr= 0;
 	else if(cfra >= seq->start+seq->len-1) nr= seq->len-1;
 	else nr= cfra-seq->start;
+	}
 
-	se+= nr;
+
+	se+= nr; /* don't get confused by the increment, this is the same as strip->stripdata[nr], which works on some compilers...*/
 	se->nr= nr;
 
 	return se;
 }
 
+ 
 void set_meta_stripdata(Sequence *seqm)
 {
 	Sequence *seq, *seqim, *seqeff;
@@ -1951,8 +1960,11 @@ void do_build_seqar_cfra(ListBase *seqbase, Sequence ***seqar, int cfra)
 						doseq= G.scene->r.scemode & R_DOSEQ;
 						G.scene->r.scemode &= ~R_DOSEQ;
 
-						/* store stuffies */
+						/* store Current FRAme */
-						oldcfra= CFRA; CFRA= seq->sfra + se->nr;
+						oldcfra= CFRA;
+
+						CFRA= ( seq->sfra + se->nr );
+
 						waitcursor(1);
 
 						rectot= R.rectot; R.rectot= NULL;