diff --git a/README.md b/README.md
index c2af1518b..374ee7a72 100755
--- a/README.md
+++ b/README.md
@@ -126,7 +126,7 @@ Supported operating systems and hardware:
 16. support live stream transcoding by ffmpeg.<br/>
 17. support live stream transcoding by ffmpeg.<br/>
 18. support ffmpeg filters(logo/overlay/crop), x264 params.<br/>
-19. [dev] support audio transcode only, speex/mp3 to aac<br/>
+19. support audio transcode only, speex/mp3 to aac<br/>
 20. [plan] support network based cli and json result.<br/>
 21. [plan] support http callback api hooks(for authentication).<br/>
 22. [plan] support bandwidth test api and flash client.<br/>
diff --git a/trunk/conf/srs.conf b/trunk/conf/srs.conf
index 94c385c67..5d6864bc9 100755
--- a/trunk/conf/srs.conf
+++ b/trunk/conf/srs.conf
@@ -15,6 +15,7 @@ log_dir             ./objs/logs;
 # default: 2000
 max_connections     2000;
 # vhost list, the __defaultVhost__ is the default vhost
+# for example, user use ip to access the stream: rtmp://192.168.1.2/live/livestream.
 # for which cannot identify the required vhost.
 # for default demo.
 vhost __defaultVhost__ {
@@ -44,7 +45,7 @@ vhost __defaultVhost__ {
             vparams {
             }
             acodec          libaacplus;
-            abitrate        30;
+            abitrate        45;
             asample_rate    44100;
             achannels       2;
             aparams {
@@ -90,7 +91,7 @@ vhost dev {
         enabled     on;
         ffmpeg      ./objs/ffmpeg/bin/ffmpeg;
         engine dev {
-            enabled         on;
+            enabled         off;
             vfilter {
             }
             vcodec          libx264;
@@ -104,7 +105,18 @@ vhost dev {
             vparams {
             }
             acodec          libaacplus;
-            abitrate        30;
+            abitrate        45;
+            asample_rate    44100;
+            achannels       2;
+            aparams {
+            }
+            output          rtmp://127.0.0.1:[port]/[app]?vhost=[vhost]/[stream]_[engine];
+        }
+        engine dev_acodec {
+            enabled         on;
+            vcodec          copy;
+            acodec          libaacplus;
+            abitrate        45;
             asample_rate    44100;
             achannels       2;
             aparams {
@@ -134,7 +146,7 @@ vhost mirror.transcode.vhost.com {
             vparams {
             }
             acodec          libaacplus;
-            abitrate        30;
+            abitrate        45;
             asample_rate    44100;
             achannels       2;
             aparams {
@@ -164,7 +176,7 @@ vhost drawtext.transcode.vhost.com {
             vparams {
             }
             acodec          libaacplus;
-            abitrate        30;
+            abitrate        45;
             asample_rate    44100;
             achannels       2;
             aparams {
@@ -194,7 +206,7 @@ vhost crop.transcode.vhost.com {
             vparams {
             }
             acodec          libaacplus;
-            abitrate        30;
+            abitrate        45;
             asample_rate    44100;
             achannels       2;
             aparams {
@@ -224,7 +236,7 @@ vhost logo.transcode.vhost.com {
             vparams {
             }
             acodec          libaacplus;
-            abitrate        30;
+            abitrate        45;
             asample_rate    44100;
             achannels       2;
             aparams {
@@ -233,6 +245,40 @@ vhost logo.transcode.vhost.com {
         }
     }
 }
+# audio transcode only.
+# for example, FMLE publish audio codec in mp3, and donot support HLS output,
+# we can transcode the audio to aac and copy video to the new stream with HLS.
+vhost audio.transcode.vhost.com {
+    transcode {
+        enabled     on;
+        ffmpeg      ./objs/ffmpeg/bin/ffmpeg;
+        engine acodec {
+            enabled         on;
+            vcodec          copy;
+            acodec          libaacplus;
+            abitrate        45;
+            asample_rate    44100;
+            achannels       2;
+            aparams {
+            }
+            output          rtmp://127.0.0.1:[port]/[app]?vhost=[vhost]/[stream]_[engine];
+        }
+    }
+}
+# ffmpeg-copy(forward implements by ffmpeg).
+# copy the video and audio to a new stream.
+vhost copy.transcode.vhost.com {
+    transcode {
+        enabled     on;
+        ffmpeg      ./objs/ffmpeg/bin/ffmpeg;
+        engine copy {
+            enabled         on;
+            vcodec          copy;
+            acodec          copy;
+            output          rtmp://127.0.0.1:[port]/[app]?vhost=[vhost]/[stream]_[engine];
+        }
+    }
+}
 # transcode all app and stream of vhost
 vhost all.transcode.vhost.com {
     # the streaming transcode configs.
@@ -258,7 +304,9 @@ vhost all.transcode.vhost.com {
                 # for filters, @see: http://ffmpeg.org/ffmpeg-filters.html
                 filter_complex      'overlay=10:10';
             }
-            # video encoder name
+            # video encoder name. can be:
+            # libx264: use h.264(libx264) video encoder.
+            # copy: donot encoder the video stream, copy it.
             vcodec          libx264;
             # video bitrate, in kbps
             vbitrate        1500;
@@ -287,7 +335,9 @@ vhost all.transcode.vhost.com {
                 bf              3;
                 refs            10;
             }
-            # audio encoder name
+            # audio encoder name. can be:
+            # libaacplus: use aac(libaacplus) audio encoder.
+            # copy: donot encoder the audio stream, copy it.
             acodec          libaacplus;
             # audio bitrate, in kbps. [16, 72] for libaacplus.
             abitrate        70;
@@ -362,13 +412,45 @@ vhost all.transcode.vhost.com {
             vparams {
             }
             acodec          libaacplus;
-            abitrate        30;
+            abitrate        45;
             asample_rate    44100;
             achannels       2;
             aparams {
             }
             output          rtmp://127.0.0.1:[port]/[app]?vhost=[vhost]/[stream]_[engine];
         }
+        engine vcopy {
+            enabled     on;
+            vcodec          copy;
+            acodec          libaacplus;
+            abitrate        45;
+            asample_rate    44100;
+            achannels       2;
+            aparams {
+            }
+            output          rtmp://127.0.0.1:[port]/[app]?vhost=[vhost]/[stream]_[engine];
+        }
+        engine acopy {
+            enabled     on;
+            vcodec          libx264;
+            vbitrate        300;
+            vfps            20;
+            vwidth          768;
+            vheight         320;
+            vthreads        2;
+            vprofile        baseline;
+            vpreset         superfast;
+            vparams {
+            }
+            acodec          copy;
+            output          rtmp://127.0.0.1:[port]/[app]?vhost=[vhost]/[stream]_[engine];
+        }
+        engine copy {
+            enabled     on;
+            vcodec          copy;
+            acodec          copy;
+            output          rtmp://127.0.0.1:[port]/[app]?vhost=[vhost]/[stream]_[engine];
+        }
     }
 }
 # transcode all stream using the empty ffmpeg demo, donothing.
@@ -389,7 +471,7 @@ vhost ffempty.transcode.vhost.com {
             vparams {
             }
             acodec          libaacplus;
-            abitrate        30;
+            abitrate        45;
             asample_rate    44100;
             achannels       2;
             aparams {
diff --git a/trunk/src/core/srs_core_encoder.cpp b/trunk/src/core/srs_core_encoder.cpp
index d0be700dd..3400948a5 100644
--- a/trunk/src/core/srs_core_encoder.cpp
+++ b/trunk/src/core/srs_core_encoder.cpp
@@ -42,8 +42,9 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 #define SRS_ENCODER_SLEEP_MS 2000
 
-#define SRS_ENCODER_VCODEC "libx264"
-#define SRS_ENCODER_ACODEC "libaacplus"
+#define SRS_ENCODER_COPY	"copy"
+#define SRS_ENCODER_VCODEC 	"libx264"
+#define SRS_ENCODER_ACODEC 	"libaacplus"
 
 // for encoder to detect the dead loop
 static std::vector<std::string> _transcoded_url;
@@ -138,70 +139,75 @@ int SrsFFMPEG::initialize(SrsRequest* req, SrsConfDirective* engine)
 	}
 	_transcoded_url.push_back(output);
 	
-	if (vcodec != SRS_ENCODER_VCODEC) {
-		ret = ERROR_ENCODER_VCODEC;
-		srs_error("invalid vcodec, must be %s, actual %s, ret=%d",
-			SRS_ENCODER_VCODEC, vcodec.c_str(), ret);
-		return ret;
+	if (vcodec != SRS_ENCODER_COPY) {
+		if (vcodec != SRS_ENCODER_VCODEC) {
+			ret = ERROR_ENCODER_VCODEC;
+			srs_error("invalid vcodec, must be %s, actual %s, ret=%d",
+				SRS_ENCODER_VCODEC, vcodec.c_str(), ret);
+			return ret;
+		}
+		if (vbitrate <= 0) {
+			ret = ERROR_ENCODER_VBITRATE;
+			srs_error("invalid vbitrate: %d, ret=%d", vbitrate, ret);
+			return ret;
+		}
+		if (vfps <= 0) {
+			ret = ERROR_ENCODER_VFPS;
+			srs_error("invalid vfps: %.2f, ret=%d", vfps, ret);
+			return ret;
+		}
+		if (vwidth <= 0) {
+			ret = ERROR_ENCODER_VWIDTH;
+			srs_error("invalid vwidth: %d, ret=%d", vwidth, ret);
+			return ret;
+		}
+		if (vheight <= 0) {
+			ret = ERROR_ENCODER_VHEIGHT;
+			srs_error("invalid vheight: %d, ret=%d", vheight, ret);
+			return ret;
+		}
+		if (vthreads < 0) {
+			ret = ERROR_ENCODER_VTHREADS;
+			srs_error("invalid vthreads: %d, ret=%d", vthreads, ret);
+			return ret;
+		}
+		if (vprofile.empty()) {
+			ret = ERROR_ENCODER_VPROFILE;
+			srs_error("invalid vprofile: %s, ret=%d", vprofile.c_str(), ret);
+			return ret;
+		}
+		if (vpreset.empty()) {
+			ret = ERROR_ENCODER_VPRESET;
+			srs_error("invalid vpreset: %s, ret=%d", vpreset.c_str(), ret);
+			return ret;
+		}
 	}
-	if (vbitrate <= 0) {
-		ret = ERROR_ENCODER_VBITRATE;
-		srs_error("invalid vbitrate: %d, ret=%d", vbitrate, ret);
-		return ret;
-	}
-	if (vfps <= 0) {
-		ret = ERROR_ENCODER_VFPS;
-		srs_error("invalid vfps: %.2f, ret=%d", vfps, ret);
-		return ret;
-	}
-	if (vwidth <= 0) {
-		ret = ERROR_ENCODER_VWIDTH;
-		srs_error("invalid vwidth: %d, ret=%d", vwidth, ret);
-		return ret;
-	}
-	if (vheight <= 0) {
-		ret = ERROR_ENCODER_VHEIGHT;
-		srs_error("invalid vheight: %d, ret=%d", vheight, ret);
-		return ret;
-	}
-	if (vthreads < 0) {
-		ret = ERROR_ENCODER_VTHREADS;
-		srs_error("invalid vthreads: %d, ret=%d", vthreads, ret);
-		return ret;
-	}
-	if (vprofile.empty()) {
-		ret = ERROR_ENCODER_VPROFILE;
-		srs_error("invalid vprofile: %s, ret=%d", vprofile.c_str(), ret);
-		return ret;
-	}
-	if (vpreset.empty()) {
-		ret = ERROR_ENCODER_VPRESET;
-		srs_error("invalid vpreset: %s, ret=%d", vpreset.c_str(), ret);
-		return ret;
-	}
-	if (acodec != SRS_ENCODER_ACODEC) {
-		ret = ERROR_ENCODER_ACODEC;
-		srs_error("invalid acodec, must be %s, actual %s, ret=%d",
-			SRS_ENCODER_ACODEC, acodec.c_str(), ret);
-		return ret;
-	}
-	if (abitrate <= 0) {
-		ret = ERROR_ENCODER_ABITRATE;
-		srs_error("invalid abitrate: %d, ret=%d", 
-			abitrate, ret);
-		return ret;
-	}
-	if (asample_rate <= 0) {
-		ret = ERROR_ENCODER_ASAMPLE_RATE;
-		srs_error("invalid sample rate: %d, ret=%d", 
-			asample_rate, ret);
-		return ret;
-	}
-	if (achannels != 1 && achannels != 2) {
-		ret = ERROR_ENCODER_ACHANNELS;
-		srs_error("invalid achannels, must be 1 or 2, actual %d, ret=%d", 
-			achannels, ret);
-		return ret;
+	
+	if (acodec != SRS_ENCODER_COPY) {
+		if (acodec != SRS_ENCODER_ACODEC) {
+			ret = ERROR_ENCODER_ACODEC;
+			srs_error("invalid acodec, must be %s, actual %s, ret=%d",
+				SRS_ENCODER_ACODEC, acodec.c_str(), ret);
+			return ret;
+		}
+		if (abitrate <= 0) {
+			ret = ERROR_ENCODER_ABITRATE;
+			srs_error("invalid abitrate: %d, ret=%d", 
+				abitrate, ret);
+			return ret;
+		}
+		if (asample_rate <= 0) {
+			ret = ERROR_ENCODER_ASAMPLE_RATE;
+			srs_error("invalid sample rate: %d, ret=%d", 
+				asample_rate, ret);
+			return ret;
+		}
+		if (achannels != 1 && achannels != 2) {
+			ret = ERROR_ENCODER_ACHANNELS;
+			srs_error("invalid achannels, must be 1 or 2, actual %d, ret=%d", 
+				achannels, ret);
+			return ret;
+		}
 	}
 	if (output.empty()) {
 		ret = ERROR_ENCODER_OUTPUT;
@@ -252,40 +258,43 @@ int SrsFFMPEG::start()
 	params.push_back("-vcodec");
 	params.push_back(vcodec);
 	
-	params.push_back("-b:v");
-	snprintf(tmp, sizeof(tmp), "%d", vbitrate * 1000);
-	params.push_back(tmp);
-	
-	params.push_back("-r");
-	snprintf(tmp, sizeof(tmp), "%.2f", vfps);
-	params.push_back(tmp);
-	
-	params.push_back("-s");
-	snprintf(tmp, sizeof(tmp), "%dx%d", vwidth, vheight);
-	params.push_back(tmp);
-	
-	// TODO: add aspect if needed.
-	params.push_back("-aspect");
-	snprintf(tmp, sizeof(tmp), "%d:%d", vwidth, vheight);
-	params.push_back(tmp);
-	
-	params.push_back("-threads");
-	snprintf(tmp, sizeof(tmp), "%d", vthreads);
-	params.push_back(tmp);
-	
-	params.push_back("-profile:v");
-	params.push_back(vprofile);
-	
-	params.push_back("-preset");
-	params.push_back(vpreset);
-	
-	// vparams
-	if (!vparams.empty()) {
-		std::vector<std::string>::iterator it;
-		for (it = vparams.begin(); it != vparams.end(); ++it) {
-			std::string p = *it;
-			if (!p.empty()) {
-				params.push_back(p);
+	// the codec params is disabled when copy
+	if (vcodec != SRS_ENCODER_COPY) {
+		params.push_back("-b:v");
+		snprintf(tmp, sizeof(tmp), "%d", vbitrate * 1000);
+		params.push_back(tmp);
+		
+		params.push_back("-r");
+		snprintf(tmp, sizeof(tmp), "%.2f", vfps);
+		params.push_back(tmp);
+		
+		params.push_back("-s");
+		snprintf(tmp, sizeof(tmp), "%dx%d", vwidth, vheight);
+		params.push_back(tmp);
+		
+		// TODO: add aspect if needed.
+		params.push_back("-aspect");
+		snprintf(tmp, sizeof(tmp), "%d:%d", vwidth, vheight);
+		params.push_back(tmp);
+		
+		params.push_back("-threads");
+		snprintf(tmp, sizeof(tmp), "%d", vthreads);
+		params.push_back(tmp);
+		
+		params.push_back("-profile:v");
+		params.push_back(vprofile);
+		
+		params.push_back("-preset");
+		params.push_back(vpreset);
+		
+		// vparams
+		if (!vparams.empty()) {
+			std::vector<std::string>::iterator it;
+			for (it = vparams.begin(); it != vparams.end(); ++it) {
+				std::string p = *it;
+				if (!p.empty()) {
+					params.push_back(p);
+				}
 			}
 		}
 	}
@@ -294,25 +303,28 @@ int SrsFFMPEG::start()
 	params.push_back("-acodec");
 	params.push_back(acodec);
 	
-	params.push_back("-b:a");
-	snprintf(tmp, sizeof(tmp), "%d", abitrate * 1000);
-	params.push_back(tmp);
-	
-	params.push_back("-ar");
-	snprintf(tmp, sizeof(tmp), "%d", asample_rate);
-	params.push_back(tmp);
-	
-	params.push_back("-ac");
-	snprintf(tmp, sizeof(tmp), "%d", achannels);
-	params.push_back(tmp);
-	
-	// aparams
-	if (!aparams.empty()) {
-		std::vector<std::string>::iterator it;
-		for (it = aparams.begin(); it != aparams.end(); ++it) {
-			std::string p = *it;
-			if (!p.empty()) {
-				params.push_back(p);
+	// the codec params is disabled when copy
+	if (acodec != SRS_ENCODER_COPY) {
+		params.push_back("-b:a");
+		snprintf(tmp, sizeof(tmp), "%d", abitrate * 1000);
+		params.push_back(tmp);
+		
+		params.push_back("-ar");
+		snprintf(tmp, sizeof(tmp), "%d", asample_rate);
+		params.push_back(tmp);
+		
+		params.push_back("-ac");
+		snprintf(tmp, sizeof(tmp), "%d", achannels);
+		params.push_back(tmp);
+		
+		// aparams
+		if (!aparams.empty()) {
+			std::vector<std::string>::iterator it;
+			for (it = aparams.begin(); it != aparams.end(); ++it) {
+				std::string p = *it;
+				if (!p.empty()) {
+					params.push_back(p);
+				}
 			}
 		}
 	}