Add some convenience operators to sequencer proxy panel:

Enable proxies for all selected movie strips (won't do recursive
enabling for metastrips yet)
Generate proxies operator here, as well as in strip menu

release/scripts/startup/bl_ui/space_sequencer.py

@@ -941,6 +941,10 @@ class SEQUENCER_PT_proxy(SequencerButtonsPanel, Panel):
 
                 col.prop(strip.proxy, "timecode")
 
+        col = layout.column()
+        col.operator("sequencer.enable_proxies")        
+        col.operator("sequencer.rebuild_proxy")
+
 
 class SEQUENCER_PT_preview(SequencerButtonsPanel_Output, Panel):
     bl_label = "Scene Preview/Render"

source/blender/blenkernel/BKE_sequencer.h

@@ -240,6 +240,7 @@ struct SeqIndexBuildContext *BKE_sequencer_proxy_rebuild_context(struct Main *bm
 void BKE_sequencer_proxy_rebuild(struct SeqIndexBuildContext *context, short *stop, short *do_update, float *progress);
 void BKE_sequencer_proxy_rebuild_finish(struct SeqIndexBuildContext *context, bool stop);
 
+void BKE_sequencer_proxy_set(struct Sequence *seq, bool value);
 /* **********************************************************************
  * seqcache.c
  *

source/blender/blenkernel/intern/sequencer.c

@@ -1644,6 +1644,22 @@ void BKE_sequencer_proxy_rebuild_finish(SeqIndexBuildContext *context, bool stop
 	MEM_freeN(context);
 }
 
+void BKE_sequencer_proxy_set(struct Sequence *seq, bool value)
+{
+	if (value) {
+		seq->flag |= SEQ_USE_PROXY;
+		if (seq->strip->proxy == NULL) {
+			seq->strip->proxy = MEM_callocN(sizeof(struct StripProxy), "StripProxy");
+			seq->strip->proxy->quality = 90;
+			seq->strip->proxy->build_tc_flags = SEQ_PROXY_TC_ALL;
+			seq->strip->proxy->build_size_flags = SEQ_PROXY_IMAGE_SIZE_25;
+		}
+	}
+	else {
+		seq->flag ^= SEQ_USE_PROXY;
+	}	
+}
+
 /*********************** color balance *************************/
 
 static StripColorBalance calc_cb(StripColorBalance *cb_)

source/blender/editors/space_sequencer/sequencer_edit.c

@@ -64,6 +64,7 @@
 #include "ED_space_api.h"
 
 #include "UI_view2d.h"
+#include "UI_interface.h"
 
 
 /* own include */
@@ -3398,6 +3399,72 @@ void SEQUENCER_OT_rebuild_proxy(wmOperatorType *ot)
 	ot->flag = OPTYPE_REGISTER;
 }
 
+static int sequencer_enable_proxies_invoke(bContext *C, wmOperator *op, const wmEvent *UNUSED(event))
+{
+	return WM_operator_props_dialog_popup(C, op, 10 * UI_UNIT_X, 5 * UI_UNIT_Y);
+}
+
+static int sequencer_enable_proxies_exec(bContext *C, wmOperator *op)
+{
+	Scene *scene = CTX_data_scene(C);
+	Editing *ed = BKE_sequencer_editing_get(scene, false);
+	Sequence *seq;
+	bool proxy_25 = RNA_boolean_get(op->ptr, "proxy_25");
+	bool proxy_50 = RNA_boolean_get(op->ptr, "proxy_50");
+	bool proxy_75 = RNA_boolean_get(op->ptr, "proxy_75");
+	bool proxy_100 = RNA_boolean_get(op->ptr, "proxy_100");
+
+	if (ed == NULL || 
+	    !(proxy_25 || proxy_50 || proxy_75 || proxy_100)) {
+		return OPERATOR_FINISHED;
+	}
+
+	SEQP_BEGIN(ed, seq)
+	{
+		if ((seq->flag & SELECT)) {
+			if (seq->type == SEQ_TYPE_MOVIE) {
+				if (!seq->strip->proxy) {
+					BKE_sequencer_proxy_set(seq, true);
+				}
+				
+				if (proxy_25)
+					seq->strip->proxy->build_size_flags |= SEQ_PROXY_IMAGE_SIZE_25;
+				if (proxy_50)
+					seq->strip->proxy->build_size_flags |= SEQ_PROXY_IMAGE_SIZE_50;
+				if (proxy_75)
+					seq->strip->proxy->build_size_flags |= SEQ_PROXY_IMAGE_SIZE_75;
+				if (proxy_100)
+					seq->strip->proxy->build_size_flags |= SEQ_PROXY_IMAGE_SIZE_100;
+			}
+		}
+	}
+	SEQ_END
+
+	WM_event_add_notifier(C, NC_SCENE | ND_SEQUENCER, scene);
+	
+	return OPERATOR_FINISHED;
+}
+
+void SEQUENCER_OT_enable_proxies(wmOperatorType *ot)
+{
+	/* identifiers */
+	ot->name = "Enable Proxies";
+	ot->idname = "SEQUENCER_OT_enable_proxies";
+	ot->description = "Enable selected proxies on all selected Movie strips";
+	
+	/* api callbacks */
+	ot->invoke = sequencer_enable_proxies_invoke;
+	ot->exec = sequencer_enable_proxies_exec;
+	
+	/* flags */
+	ot->flag = OPTYPE_REGISTER;
+	
+	RNA_def_boolean(ot->srna, "proxy_25", false, "25%", "");
+	RNA_def_boolean(ot->srna, "proxy_50", false, "50%", "");
+	RNA_def_boolean(ot->srna, "proxy_75", false, "75%", "");
+	RNA_def_boolean(ot->srna, "proxy_100", false, "100%", "");
+}
+
 /* change ops */
 
 static EnumPropertyItem prop_change_effect_input_types[] = {

source/blender/editors/space_sequencer/sequencer_intern.h

@@ -131,6 +131,7 @@ void SEQUENCER_OT_copy(struct wmOperatorType *ot);
 void SEQUENCER_OT_paste(struct wmOperatorType *ot);
 
 void SEQUENCER_OT_rebuild_proxy(struct wmOperatorType *ot);
+void SEQUENCER_OT_enable_proxies(struct wmOperatorType *ot);
 
 /* preview specific operators */
 void SEQUENCER_OT_view_all_preview(struct wmOperatorType *ot);

source/blender/editors/space_sequencer/sequencer_ops.c

@@ -88,6 +88,7 @@ void sequencer_operatortypes(void)
 	WM_operatortype_append(SEQUENCER_OT_view_ghost_border);
 
 	WM_operatortype_append(SEQUENCER_OT_rebuild_proxy);
+	WM_operatortype_append(SEQUENCER_OT_enable_proxies);
 	WM_operatortype_append(SEQUENCER_OT_change_effect_input);
 	WM_operatortype_append(SEQUENCER_OT_change_effect_type);
 	WM_operatortype_append(SEQUENCER_OT_change_path);

source/blender/makesrna/intern/rna_sequencer.c

@@ -310,18 +310,7 @@ static void rna_Sequence_frame_offset_range(PointerRNA *ptr, int *min, int *max,
 static void rna_Sequence_use_proxy_set(PointerRNA *ptr, int value)
 {
 	Sequence *seq = (Sequence *)ptr->data;
-	if (value) {
-		seq->flag |= SEQ_USE_PROXY;
-		if (seq->strip->proxy == NULL) {
-			seq->strip->proxy = MEM_callocN(sizeof(struct StripProxy), "StripProxy");
-			seq->strip->proxy->quality = 90;
-			seq->strip->proxy->build_tc_flags = SEQ_PROXY_TC_ALL;
-			seq->strip->proxy->build_size_flags = SEQ_PROXY_IMAGE_SIZE_25;
-		}
-	}
-	else {
-		seq->flag ^= SEQ_USE_PROXY;
-	}
+	BKE_sequencer_proxy_set(seq, value != 0);
 }
 
 static void rna_Sequence_use_translation_set(PointerRNA *ptr, int value)