Optimize short-term prediction by reducing index arithmetic.

[ffmpeg] / libavcodec / mpegvideo_parser.c

diff --git a/libavcodec/mpegvideo_parser.c b/libavcodec/mpegvideo_parser.c
index 215c86c4001b1e23269f6fbf04a4e7fbe78ae4d0..28ed590320b3e9a662d1d38abe391dc218dd3b65 100644 (file)
--- a/libavcodec/mpegvideo_parser.c
+++ b/libavcodec/mpegvideo_parser.c
@@ -28,15 +28,16 @@ static void mpegvideo_extract_headers(AVCodecParserContext *s,
                                       const uint8_t *buf, int buf_size)
 {
     ParseContext1 *pc = s->priv_data;
-    const uint8_t *buf_end;
+    const uint8_t *buf_end = buf + buf_size;
     uint32_t start_code;
     int frame_rate_index, ext_type, bytes_left;
     int frame_rate_ext_n, frame_rate_ext_d;
     int picture_structure, top_field_first, repeat_first_field, progressive_frame;
     int horiz_size_ext, vert_size_ext, bit_rate_ext;
+    int did_set_size=0;
 //FIXME replace the crap with get_bits()
     s->repeat_pict = 0;
-    buf_end = buf + buf_size;
+
     while (buf < buf_end) {
         start_code= -1;
         buf= ff_find_start_code(buf, buf_end, &start_code);
@@ -51,7 +52,10 @@ static void mpegvideo_extract_headers(AVCodecParserContext *s,
             if (bytes_left >= 7) {
                 pc->width  = (buf[0] << 4) | (buf[1] >> 4);
                 pc->height = ((buf[1] & 0x0f) << 8) | buf[2];
-                avcodec_set_dimensions(avctx, pc->width, pc->height);
+                if(!avctx->width || !avctx->height || !avctx->coded_width || !avctx->coded_height){
+                    avcodec_set_dimensions(avctx, pc->width, pc->height);
+                    did_set_size=1;
+                }
                 frame_rate_index = buf[3] & 0xf;
                 pc->frame_rate.den = avctx->time_base.den = ff_frame_rate_tab[frame_rate_index].num;
                 pc->frame_rate.num = avctx->time_base.num = ff_frame_rate_tab[frame_rate_index].den;
@@ -77,7 +81,8 @@ static void mpegvideo_extract_headers(AVCodecParserContext *s,
                         pc->width  |=(horiz_size_ext << 12);
                         pc->height |=( vert_size_ext << 12);
                         avctx->bit_rate += (bit_rate_ext << 18) * 400;
-                        avcodec_set_dimensions(avctx, pc->width, pc->height);
+                        if(did_set_size)
+                            avcodec_set_dimensions(avctx, pc->width, pc->height);
                         avctx->time_base.den = pc->frame_rate.den * (frame_rate_ext_n + 1) * 2;
                         avctx->time_base.num = pc->frame_rate.num * (frame_rate_ext_d + 1);
                         avctx->codec_id = CODEC_ID_MPEG2VIDEO;