examples/decoding_encoding: re-organize frame configuration code

Put the relevant code in one chunk, also check for frame allocation
failures.

doc/examples/decoding_encoding.c

@@ -332,7 +332,6 @@ static void video_encode_example(const char *filename, int codec_id)
     }
 
     c = avcodec_alloc_context3(codec);
-    picture= avcodec_alloc_frame();
 
     /* put sample parameters */
     c->bit_rate = 400000;
@@ -360,6 +359,15 @@ static void video_encode_example(const char *filename, int codec_id)
         exit(1);
     }
 
+    picture = avcodec_alloc_frame();
+    if (!picture) {
+        fprintf(stderr, "Could not allocate video frame\n");
+        exit(1);
+    }
+    picture->format = c->pix_fmt;
+    picture->width  = c->width;
+    picture->height = c->height;
+
     /* the image can be allocated by any means and av_image_alloc() is
      * just the most convenient way if av_malloc() is to be used */
     ret = av_image_alloc(picture->data, picture->linesize, c->width, c->height,
@@ -369,10 +377,6 @@ static void video_encode_example(const char *filename, int codec_id)
         exit(1);
     }
 
-    picture->format = c->pix_fmt;
-    picture->width  = c->width;
-    picture->height = c->height;
-
     /* encode 1 second of video */
     for(i=0;i<25;i++) {
         av_init_packet(&pkt);
@@ -483,8 +487,6 @@ static void video_decode_example(const char *outfilename, const char *filename)
     }
 
     c = avcodec_alloc_context3(codec);
-    picture= avcodec_alloc_frame();
-
     if(codec->capabilities&CODEC_CAP_TRUNCATED)
         c->flags|= CODEC_FLAG_TRUNCATED; /* we do not send complete frames */
 
@@ -506,6 +508,12 @@ static void video_decode_example(const char *outfilename, const char *filename)
         exit(1);
     }
 
+    picture = avcodec_alloc_frame();
+    if (!picture) {
+        fprintf(stderr, "Could not allocate video frame\n");
+        exit(1);
+    }
+
     frame = 0;
     for(;;) {
         avpkt.size = fread(inbuf, 1, INBUF_SIZE, f);