fix build ffmpeg bug, add -ldl compile option

@@ -81,7 +81,7 @@ else
         --prefix=${ff_release_dir} --cc= \
         --enable-static --disable-shared --disable-debug \
         --extra-cflags='-I${ffmpeg_exported_release_dir}/include' \
-        --extra-ldflags='-L${ffmpeg_exported_release_dir}/lib -lm' \
+        --extra-ldflags='-L${ffmpeg_exported_release_dir}/lib -lm -ldl' \
         --disable-ffplay --disable-ffprobe --disable-ffserver --disable-doc \
         --enable-postproc --enable-bzlib --enable-zlib --enable-parsers \
         --enable-libx264 --enable-libmp3lame --enable-libaacplus \

@@ -17,6 +17,7 @@ vhost __defaultVhost__ {
     hls_window      30;
     #forward         127.0.0.1:1936;
     transcode {
+        enabled     on;
         ffmpeg      ./objs/ffmpeg/bin/ffmpeg;
         engine fd{
             vcodec          libx264;
@@ -39,7 +40,11 @@ vhost __defaultVhost__ {
 }
 # transcode all app and stream of vhost
 vhost all.transcode.vhost.com {
+    # the streaming transcode configs.
     transcode {
+        # whether the transcode enabled.
+        # if off, donot transcode.
+        enabled     on;
         # the ffmpeg 
         ffmpeg ./objs/ffmpeg/bin/ffmpeg;
         # all matched stream will transcoded to the following stream.
@@ -95,12 +100,14 @@ vhost all.transcode.vhost.com {
             vthreads        6;
             vprofile        main;
             vpreset         medium;
-            vparams {}
+            vparams {
+            }
             acodec          libaacplus;
             abitrate        70;
             asample_rate    44100;
             achannels       2;
-            aparams {}
+            aparams {
+            }
             output          rtmp://[vhost]:[port]/[app]/[stream]_hd;
         }
         engine sd{
@@ -112,12 +119,14 @@ vhost all.transcode.vhost.com {
             vthreads        4;
             vprofile        main;
             vpreset         fast;
-            vparams {}
+            vparams {
+            }
             acodec          libaacplus;
             abitrate        60;
             asample_rate    44100;
             achannels       2;
-            aparams {}
+            aparams {
+            }
             output          rtmp://[vhost]:[port]/[app]/[stream]_sd;
         }
         engine fast{
@@ -129,12 +138,14 @@ vhost all.transcode.vhost.com {
             vthreads        2;
             vprofile        baseline;
             vpreset         superfast;
-            vparams {}
+            vparams {
+            }
             acodec          libaacplus;
             abitrate        30;
             asample_rate    22050;
             achannels       2;
-            aparams {}
+            aparams {
+            }
             output          rtmp://[vhost]:[port]/[app]/[stream]_fast;
         }
     }