Fix build for ffmpeg-3.0.
Based on a patch by Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
for ffmpeg-2.9, found at <https://gnunet.org/bugs/view.php?id=4167>
and later modified by Mark H Weaver <mhw@netris.org> for ffmpeg-3.0.

--- libextractor-1.3/src/plugins/thumbnailffmpeg_extractor.c.orig	2013-12-21 11:04:41.000000000 -0500
+++ libextractor-1.3/src/plugins/thumbnailffmpeg_extractor.c	2016-04-04 22:42:17.859001669 -0400
@@ -153,7 +153,7 @@
 static size_t 
 create_thumbnail (int src_width, int src_height, 
 		  int src_stride[],
-		  enum PixelFormat src_pixfmt, 
+		  enum AVPixelFormat src_pixfmt,
 		  const uint8_t * const src_data[],
 		  int dst_width, int dst_height,
 		  uint8_t **output_data, 
@@ -189,7 +189,7 @@
   if (NULL == 
       (scaler_ctx =
        sws_getContext (src_width, src_height, src_pixfmt,
-		       dst_width, dst_height, PIX_FMT_RGB24, 
+		       dst_width, dst_height, AV_PIX_FMT_RGB24,
 		       SWS_BILINEAR, NULL, NULL, NULL)))
     {
 #if DEBUG
@@ -199,7 +199,7 @@
       return 0;
     }
 
-  if (NULL == (dst_frame = avcodec_alloc_frame ()))
+  if (NULL == (dst_frame = av_frame_alloc ()))
     {
 #if DEBUG
       fprintf (stderr,
@@ -209,7 +209,7 @@
       return 0;
     }
   if (NULL == (dst_buffer =
-	       av_malloc (avpicture_get_size (PIX_FMT_RGB24, dst_width, dst_height))))
+	       av_malloc (avpicture_get_size (AV_PIX_FMT_RGB24, dst_width, dst_height))))
     {
 #if DEBUG
       fprintf (stderr,
@@ -220,7 +220,7 @@
       return 0;
     }
   avpicture_fill ((AVPicture *) dst_frame, dst_buffer,
-                  PIX_FMT_RGB24, dst_width, dst_height);
+                  AV_PIX_FMT_RGB24, dst_width, dst_height);
   sws_scale (scaler_ctx,
              src_data, 
              src_stride,
@@ -255,7 +255,7 @@
     }
   encoder_codec_ctx->width = dst_width;
   encoder_codec_ctx->height = dst_height;
-  encoder_codec_ctx->pix_fmt = PIX_FMT_RGB24;
+  encoder_codec_ctx->pix_fmt = AV_PIX_FMT_RGB24;
   opts = NULL;
   if (avcodec_open2 (encoder_codec_ctx, encoder_codec, &opts) < 0)
     {
@@ -410,7 +410,7 @@
       return;
     }
   av_dict_free (&opts);
-  if (NULL == (frame = avcodec_alloc_frame ()))
+  if (NULL == (frame = av_frame_alloc ()))
     {
 #if DEBUG
       fprintf (stderr,
@@ -563,7 +563,7 @@
       return;
     }
 
-  if (NULL == (frame = avcodec_alloc_frame ()))
+  if (NULL == (frame = av_frame_alloc ()))
     {
 #if DEBUG
       fprintf (stderr,
--- libextractor-1.3/src/plugins/previewopus_extractor.c.orig	2013-12-22 17:44:18.000000000 -0500
+++ libextractor-1.3/src/plugins/previewopus_extractor.c	2016-04-04 22:49:05.168105265 -0400
@@ -296,7 +296,7 @@
 /** Initialize one audio frame for reading from the input file */
 static int init_input_frame(AVFrame **frame)
 {
-    if (!(*frame = avcodec_alloc_frame())) {
+    if (!(*frame = av_frame_alloc())) {
  #if DEBUG
         fprintf(stderr, "Could not allocate input frame\n");
 #endif
@@ -655,7 +655,7 @@
         av_freep(&converted_input_samples[0]);
         free(converted_input_samples);
     }
-    avcodec_free_frame(&input_frame);
+    av_frame_free(&input_frame);
 
     return ret;
 }
@@ -671,7 +671,7 @@
     int error;
 
     /** Create a new frame to store the audio samples. */
-    if (!(*frame = avcodec_alloc_frame())) {
+    if (!(*frame = av_frame_alloc())) {
         #if DEBUG
 		fprintf(stderr, "Could not allocate output frame\n");
 		#endif
@@ -702,7 +702,7 @@
         #if DEBUG
 		fprintf(stderr, "Could allocate output frame samples (error '%s')\n", get_error_text(error));
 		#endif
-        avcodec_free_frame(frame);
+        av_frame_free(frame);
         return error;
     }
 
@@ -783,17 +783,17 @@
         #if DEBUG
 		fprintf(stderr, "Could not read data from FIFO\n");
 		#endif
-        avcodec_free_frame(&output_frame);
+        av_frame_free(&output_frame);
         return AVERROR_EXIT;
     }
 
     /** Encode one frame worth of audio samples. */
     if (encode_audio_frame(output_frame, output_format_context,
                            output_codec_context, &data_written)) {
-        avcodec_free_frame(&output_frame);
+        av_frame_free(&output_frame);
         return AVERROR_EXIT;
     }
-    avcodec_free_frame(&output_frame);
+    av_frame_free(&output_frame);
     return 0;
 }
 /** Write the trailer of the output file container. */
@@ -907,7 +907,7 @@
       return;
     }
 
-  if (NULL == (frame = avcodec_alloc_frame ()))
+  if (NULL == (frame = av_frame_alloc ()))
     {
 #if DEBUG
       fprintf (stderr,