Check that the device is a capture device immediately after opening

the device.

Originally committed as revision 16318 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavdevice/v4l.c

@@ -103,14 +103,6 @@ static int grab_read_header(AVFormatContext *s1, AVFormatParameters *ap)
         goto fail;
     }
 
-    /* no values set, autodetect them */
-    if (s->video_win.width <= 0 || s->video_win.height <= 0) {
-        if (ioctl(video_fd, VIDIOCGWIN, &s->video_win, sizeof(s->video_win)) < 0) {
-            av_log(s1, AV_LOG_ERROR, "VIDIOCGWIN: %s\n", strerror(errno));
-            goto fail;
-        }
-    }
-
     if (ioctl(video_fd, VIDIOCGCAP, &s->video_cap) < 0) {
         av_log(s1, AV_LOG_ERROR, "VIDIOCGCAP: %s\n", strerror(errno));
         goto fail;
@@ -121,6 +113,14 @@ static int grab_read_header(AVFormatContext *s1, AVFormatParameters *ap)
         goto fail;
     }
 
+    /* no values set, autodetect them */
+    if (s->video_win.width <= 0 || s->video_win.height <= 0) {
+        if (ioctl(video_fd, VIDIOCGWIN, &s->video_win, sizeof(s->video_win)) < 0) {
+            av_log(s1, AV_LOG_ERROR, "VIDIOCGWIN: %s\n", strerror(errno));
+            goto fail;
+        }
+    }
+
     desired_palette = -1;
     desired_depth = -1;
     for (j = 0; j < vformat_num; j++) {