add ffmpeg build script

 http-parser-2.1.zip
-	for srs to support http callback.
+    for srs to support http callback.
 
 nginx-1.5.7.zip
-	for srs to support hls streaming.
+    for srs to support hls streaming.
 
 st-1.9.zip
-	basic framework for srs.
+    basic framework for srs.
 
 ffmpeg-2.1.1.tar.gz
 yasm-1.2.0.tar.gz
@@ -13,29 +13,29 @@ lame-3.99.5.tar.gz
 libaacplus-2.0.2.tar.gz
 libaacplus-patch-26410-800.zip (26410-800.zip)
 x264-snapshot-20131129-2245-stable.tar.bz2 (core.138)
-	for srs to support live stream transcoding.
-	remark: we use *.zip for all linux plantform.
+    for srs to support live stream transcoding.
+    remark: we use *.zip for all linux plantform.
 
 tools/ccache-3.1.9.zip
-	to fast build.
+    to fast build.
 
 links:
-	ffmpeg: 
-		http://ffmpeg.org/ 
-		http://ffmpeg.org/releases/ffmpeg-2.1.1.tar.gz
-	x264: 
-		http://www.videolan.org/ 
-		ftp://ftp.videolan.org/pub/videolan/x264/snapshots/x264-snapshot-20131129-2245-stable.tar.bz2
-	lame: 
-		http://sourceforge.net/projects/lame/ 
-		http://nchc.dl.sourceforge.net/project/lame/lame/3.99/lame-3.99.5.tar.gz
-	aacplus: 
-		http://217.20.164.161/~tipok/aacplus/ 
-		http://217.20.164.161/~tipok/aacplus/libaacplus-2.0.2.tar.gz
-	aacplus-patch: 
-		http://www.3gpp.org/DynaReport/26410.htm 
-		http://www.3gpp.org/ftp/Specs/archive/26_series/26.410/26410-800.zip
-	yasm:
-		http://yasm.tortall.net/
-		http://www.tortall.net/projects/yasm/releases/yasm-1.2.0.tar.gz
+    ffmpeg: 
+        http://ffmpeg.org/ 
+        http://ffmpeg.org/releases/ffmpeg-2.1.1.tar.gz
+    x264: 
+        http://www.videolan.org/ 
+        ftp://ftp.videolan.org/pub/videolan/x264/snapshots/x264-snapshot-20131129-2245-stable.tar.bz2
+    lame: 
+        http://sourceforge.net/projects/lame/ 
+        http://nchc.dl.sourceforge.net/project/lame/lame/3.99/lame-3.99.5.tar.gz
+    aacplus: 
+        http://217.20.164.161/~tipok/aacplus/ 
+        http://217.20.164.161/~tipok/aacplus/libaacplus-2.0.2.tar.gz
+    aacplus-patch: 
+        http://www.3gpp.org/DynaReport/26410.htm 
+        http://www.3gpp.org/ftp/Specs/archive/26_series/26.410/26410-800.zip
+    yasm:
+        http://yasm.tortall.net/
+        http://www.tortall.net/projects/yasm/releases/yasm-1.2.0.tar.gz
 

@@ -96,7 +96,7 @@ if [ $SRS_FFMPEG = YES ]; then
             cd ${SRS_OBJS} && pwd_dir=`pwd` && 
             rm -rf ffmepg.src && mkdir -p ffmpeg.src && cd ffmpeg.src &&
             rm -f build_ffmpeg.sh && ln -sf ../../auto/build_ffmpeg.sh && . build_ffmpeg.sh &&
-            cd ${pwd_dir} && ln -sf ffmepg.src/_release ffmpeg
+            cd ${pwd_dir} && ln -sf ffmpeg.src/_release ffmpeg
         )
     fi
     # check status