examples: Fix use of AV_CODEC_FLAG_GLOBAL_HEADER

AV_CODEC_FLAG_GLOBAL_HEADER should be set before calling avcodec_open2() to have any effect.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit a82e4fb8)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

doc/examples/transcoding.c

@@ -173,6 +173,9 @@ static int open_output_file(const char *filename)
                 enc_ctx->time_base = (AVRational){1, enc_ctx->sample_rate};
             }
 
+            if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)
+                enc_ctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
+
             /* Third parameter can be used to pass settings to encoder */
             ret = avcodec_open2(enc_ctx, encoder, NULL);
             if (ret < 0) {
@@ -184,8 +187,6 @@ static int open_output_file(const char *filename)
                 av_log(NULL, AV_LOG_ERROR, "Failed to copy encoder parameters to output stream #%u\n", i);
                 return ret;
             }
-            if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)
-                enc_ctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
 
             out_stream->time_base = enc_ctx->time_base;
             stream_ctx[i].enc_ctx = enc_ctx;