diff --git a/trunk/src/app/srs_app_avc_aac.cpp b/trunk/src/app/srs_app_avc_aac.cpp
index 0d9b622fc..830979223 100644
--- a/trunk/src/app/srs_app_avc_aac.cpp
+++ b/trunk/src/app/srs_app_avc_aac.cpp
@@ -29,6 +29,7 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 #include <srs_kernel_log.hpp>
 #include <srs_kernel_codec.hpp>
 #include <srs_kernel_stream.hpp>
+#include <srs_protocol_amf0.hpp>
 
 SrsCodecSampleUnit::SrsCodecSampleUnit()
 {
@@ -120,6 +121,51 @@ SrsAvcAacCodec::~SrsAvcAacCodec()
     srs_freep(pictureParameterSetNALUnit);
 }
 
+int SrsAvcAacCodec::metadata_demux(SrsAmf0Object* metadata)
+{
+    int ret = ERROR_SUCCESS;
+    
+    srs_assert(metadata);
+    
+    SrsAmf0Object* obj = metadata;
+    
+    //    finger out the codec info from metadata if possible.
+    SrsAmf0Any* prop = NULL;
+
+    if ((prop = obj->get_property("duration")) != NULL && prop->is_number()) {
+        duration = (int)prop->to_number();
+    }
+    if ((prop = obj->get_property("width")) != NULL && prop->is_number()) {
+        width = (int)prop->to_number();
+    }
+    if ((prop = obj->get_property("height")) != NULL && prop->is_number()) {
+        height = (int)prop->to_number();
+    }
+    if ((prop = obj->get_property("framerate")) != NULL && prop->is_number()) {
+        frame_rate = (int)prop->to_number();
+    }
+    if ((prop = obj->get_property("videocodecid")) != NULL && prop->is_number()) {
+        video_codec_id = (int)prop->to_number();
+    }
+    if ((prop = obj->get_property("videodatarate")) != NULL && prop->is_number()) {
+        video_data_rate = (int)(1000 * prop->to_number());
+    }
+    
+    if ((prop = obj->get_property("audiocodecid")) != NULL && prop->is_number()) {
+        audio_codec_id = (int)prop->to_number();
+    }
+    if ((prop = obj->get_property("audiodatarate")) != NULL && prop->is_number()) {
+        audio_data_rate = (int)(1000 * prop->to_number());
+    }
+    
+    // ignore the following, for each flv/rtmp packet contains them:
+    // audiosamplerate, sample->sound_rate
+    // audiosamplesize, sample->sound_size
+    // stereo,             sample->sound_type
+    
+    return ret;
+}
+
 int SrsAvcAacCodec::audio_aac_demux(char* data, int size, SrsCodecSample* sample)
 {
     int ret = ERROR_SUCCESS;
@@ -142,6 +188,7 @@ int SrsAvcAacCodec::audio_aac_demux(char* data, int size, SrsCodecSample* sample
         return ret;
     }
     
+    // @see: E.4.2 Audio Tags, video_file_format_spec_v10_1.pdf, page 76
     int8_t sound_format = stream->read_1bytes();
     
     int8_t sound_type = sound_format & 0x01;
diff --git a/trunk/src/app/srs_app_avc_aac.hpp b/trunk/src/app/srs_app_avc_aac.hpp
index e84b2e9ca..f29c9c8c2 100644
--- a/trunk/src/app/srs_app_avc_aac.hpp
+++ b/trunk/src/app/srs_app_avc_aac.hpp
@@ -33,6 +33,7 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 #include <srs_kernel_codec.hpp>
 
 class SrsStream;
+class SrsAmf0Object;
 
 #define SRS_MAX_CODEC_SAMPLE 128
 #define _SRS_AAC_SAMPLE_RATE_UNSET 15
@@ -223,31 +224,59 @@ public:
 public:
     /**
     * audio specified
+    * 1.6.2.1 AudioSpecificConfig, in aac-mp4a-format-ISO_IEC_14496-3+2001.pdf, page 33.
+    * audioObjectType, value defines in 7.1 Profiles, aac-iso-13818-7.pdf, page 40.
     */
-    // 1.6.2.1 AudioSpecificConfig, in aac-mp4a-format-ISO_IEC_14496-3+2001.pdf, page 33.
-    // audioObjectType, value defines in 7.1 Profiles, aac-iso-13818-7.pdf, page 40.
     u_int8_t        aac_profile; 
-    // samplingFrequencyIndex
+    /**
+    * samplingFrequencyIndex
+    */
     u_int8_t        aac_sample_rate;
-    // channelConfiguration
+    /**
+    * channelConfiguration
+    */
     u_int8_t        aac_channels;
 public:
-    // the avc extra data, the AVC sequence header,
-    // without the flv codec header,
-    // @see: ffmpeg, AVCodecContext::extradata
+    /**
+    * the avc extra data, the AVC sequence header,
+    * without the flv codec header,
+    * @see: ffmpeg, AVCodecContext::extradata
+    */
     int             avc_extra_size;
     char*           avc_extra_data;
-    // the aac extra data, the AAC sequence header,
-    // without the flv codec header,
-    // @see: ffmpeg, AVCodecContext::extradata
+    /**
+    * the aac extra data, the AAC sequence header,
+    * without the flv codec header,
+    * @see: ffmpeg, AVCodecContext::extradata
+    */
     int             aac_extra_size;
     char*           aac_extra_data;
 public:
     SrsAvcAacCodec();
     virtual ~SrsAvcAacCodec();
-// the following function used for hls to build the codec info.
+// the following function used for hls to build the sample and codec.
 public:
+    /**
+    * demux the metadata, to to get the stream info,
+    * for instance, the width/height, sample rate.
+    * @param metadata, the metadata amf0 object. assert not NULL.
+    */
+    virtual int metadata_demux(SrsAmf0Object* metadata);
+    /**
+    * demux the audio packet in aac codec.
+    * the packet mux in FLV/RTMP format defined in flv specification.
+    * demux the audio speicified data(sound_format, sound_size, ...) to sample.
+    * demux the aac specified data(aac_profile, ...) to codec from sequence header.
+    * demux the aac raw to sample units.
+    */
     virtual int audio_aac_demux(char* data, int size, SrsCodecSample* sample);
+    /**
+    * demux the video packet in h.264 codec.
+    * the packet mux in FLV/RTMP format defined in flv specification.
+    * demux the video specified data(frame_type, codec_id, ...) to sample.
+    * demux the h.264 sepcified data(avc_profile, ...) to codec from sequence header.
+    * demux the h.264 NALUs to sampe units.
+    */
     virtual int video_avc_demux(char* data, int size, SrsCodecSample* sample);
 };
 
diff --git a/trunk/src/app/srs_app_hls.cpp b/trunk/src/app/srs_app_hls.cpp
index 6138ea75f..af82fd293 100644
--- a/trunk/src/app/srs_app_hls.cpp
+++ b/trunk/src/app/srs_app_hls.cpp
@@ -1415,45 +1415,14 @@ int SrsHls::on_meta_data(SrsAmf0Object* metadata)
         return ret;
     }
     
-    SrsAmf0Object* obj = metadata;
-    if (obj->count() <= 0) {
+    if (metadata->count() <= 0) {
         srs_trace("no metadata persent, hls ignored it.");
         return ret;
     }
     
-    //    finger out the codec info from metadata if possible.
-    SrsAmf0Any* prop = NULL;
-
-    if ((prop = obj->get_property("duration")) != NULL && prop->is_number()) {
-        codec->duration = (int)prop->to_number();
+    if ((ret = codec->metadata_demux(metadata)) != ERROR_SUCCESS) {
+        return ret;
     }
-    if ((prop = obj->get_property("width")) != NULL && prop->is_number()) {
-        codec->width = (int)prop->to_number();
-    }
-    if ((prop = obj->get_property("height")) != NULL && prop->is_number()) {
-        codec->height = (int)prop->to_number();
-    }
-    if ((prop = obj->get_property("framerate")) != NULL && prop->is_number()) {
-        codec->frame_rate = (int)prop->to_number();
-    }
-    if ((prop = obj->get_property("videocodecid")) != NULL && prop->is_number()) {
-        codec->video_codec_id = (int)prop->to_number();
-    }
-    if ((prop = obj->get_property("videodatarate")) != NULL && prop->is_number()) {
-        codec->video_data_rate = (int)(1000 * prop->to_number());
-    }
-    
-    if ((prop = obj->get_property("audiocodecid")) != NULL && prop->is_number()) {
-        codec->audio_codec_id = (int)prop->to_number();
-    }
-    if ((prop = obj->get_property("audiodatarate")) != NULL && prop->is_number()) {
-        codec->audio_data_rate = (int)(1000 * prop->to_number());
-    }
-    
-    // ignore the following, for each flv/rtmp packet contains them:
-    // audiosamplerate, sample->sound_rate
-    // audiosamplesize, sample->sound_size
-    // stereo,             sample->sound_type
     
     return ret;
 }