ansi: erase screen on first frame

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/ansi.c

@@ -58,6 +58,7 @@ typedef struct {
     int attributes;       /**< attribute flags */
     int fg;               /**< foreground color */
     int bg;               /**< background color */
+    int first_frame;
 
     /* ansi parser state machine */
     enum {
@@ -353,6 +354,10 @@ static int decode_frame(AVCodecContext *avctx,
     s->frame.pict_type           = AV_PICTURE_TYPE_I;
     s->frame.palette_has_changed = 1;
     set_palette((uint32_t *)s->frame.data[1]);
+    if (!s->first_frame) {
+        erase_screen(avctx);
+        s->first_frame = 1;
+    }
 
     while(buf < buf_end) {
         switch(s->state) {

tests/ref/fate/ansi

@@ -1,7 +1,7 @@
 #tb 0: 1/25
-0,          0,          0,        1,   768000, 0xc4865718
-0,          1,          1,        1,   768000, 0x2c7de258
-0,          2,          2,        1,   768000, 0x0d6b8dc6
+0,          0,          0,        1,   768000, 0x772dd3d0
+0,          1,          1,        1,   768000, 0xd7dab1d1
+0,          2,          2,        1,   768000, 0x0e56f2d3
 0,          3,          3,        1,   768000, 0x11c1fb8e
 0,          4,          4,        1,   768000, 0x72d12da9
 0,          5,          5,        1,   768000, 0x39c7a70d