lavd/fbdev_enc: add default device

Use device specified by environment variable FRAMEBUFFER or /dev/fb0 as default.
Signed-off-by: Lukasz Marek <lukasz.m.luki@gmail.com>

libavdevice/fbdev_common.c

@@ -20,6 +20,7 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#include <stdlib.h>
 #include "fbdev_common.h"
 #include "libavutil/common.h"
 
@@ -55,3 +56,12 @@ enum AVPixelFormat ff_get_pixfmt_from_fb_varinfo(struct fb_var_screeninfo *varin
 
     return AV_PIX_FMT_NONE;
 }
+
+const char* ff_fbdev_default_device()
+{
+    const char *dev = getenv("FRAMEBUFFER");
+    if (!dev)
+        dev = "/dev/fb0";
+    return dev;
+}
+

libavdevice/fbdev_common.h

@@ -29,4 +29,6 @@
 
 enum AVPixelFormat ff_get_pixfmt_from_fb_varinfo(struct fb_var_screeninfo *varinfo);
 
+const char* ff_fbdev_default_device(void);
+
 #endif /* AVDEVICE_FBDEV_COMMON_H */

libavdevice/fbdev_enc.c

@@ -45,17 +45,23 @@ static av_cold int fbdev_write_header(AVFormatContext *h)
     FBDevContext *fbdev = h->priv_data;
     enum AVPixelFormat pix_fmt;
     int ret, flags = O_RDWR;
+    const char* device;
 
     if (h->nb_streams != 1 || h->streams[0]->codec->codec_type != AVMEDIA_TYPE_VIDEO) {
         av_log(fbdev, AV_LOG_ERROR, "Only a single video stream is supported.\n");
         return AVERROR(EINVAL);
     }
 
-    if ((fbdev->fd = avpriv_open(h->filename, flags)) == -1) {
+    if (h->filename[0])
+        device = h->filename;
+    else
+        device = ff_fbdev_default_device();
+
+    if ((fbdev->fd = avpriv_open(device, flags)) == -1) {
         ret = AVERROR(errno);
         av_log(h, AV_LOG_ERROR,
                "Could not open framebuffer device '%s': %s\n",
-               h->filename, av_err2str(ret));
+               device, av_err2str(ret));
         return ret;
     }