diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..8864d4a
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2017 
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/decoder.go b/decoder.go
index 2502503..a54c8cd 100644
--- a/decoder.go
+++ b/decoder.go
@@ -18,6 +18,12 @@ type decoder struct {
 	codecType  int
 }
 
+func decodeAVPacket(packet *C.AVPacket) (data []byte) {
+	data = make([]byte, int(packet.size))
+	copy(data, *(*[]byte)(unsafe.Pointer(&packet.data)))
+	return
+}
+
 func (decoder *decoder) Decode(packet *C.AVPacket) (pkt *Packet, err error) {
 	pkt = &Packet{}
 
@@ -47,10 +53,14 @@ func (decoder *decoder) Decode(packet *C.AVPacket) (pkt *Packet, err error) {
 		return
 	}
 
+	pkt.duration = int64(frame.pkt_duration)
+	pkt.position = int64(frame.pkt_pos)
+
 	switch decoder.codecType {
 	case C.AVMEDIA_TYPE_VIDEO:
 		pkt.width = int(frame.width)
 		pkt.height = int(frame.height)
+		pkt.keyFrame = int(frame.key_frame) == 1
 
 		var encPacket C.AVPacket
 		defer C.av_packet_unref(&encPacket)
@@ -69,8 +79,7 @@ func (decoder *decoder) Decode(packet *C.AVPacket) (pkt *Packet, err error) {
 			}
 		}
 
-		pkt.data = make([]byte, int(encPacket.size))
-		copy(pkt.data, *(*[]byte)(unsafe.Pointer(&encPacket.data)))
+		pkt.data = decodeAVPacket(&encPacket)
 
 	case C.AVMEDIA_TYPE_AUDIO:
 		pkt.bitRate = int(decoder.codecCtx.bit_rate)
@@ -108,8 +117,7 @@ func (decoder *decoder) Decode(packet *C.AVPacket) (pkt *Packet, err error) {
 				err = fmt.Errorf("ffmpeg: rtsp_avcodec_encode_resample_wav failed: %d", cerr)
 				return
 			}
-			pkt.data = make([]byte, int(encPacket.size))
-			copy(pkt.data, *(*[]byte)(unsafe.Pointer(&encPacket.data)))
+			pkt.data = decodeAVPacket(&encPacket)
 
 		case C.AV_SAMPLE_FMT_S16:
 			var encPacket C.AVPacket
@@ -119,9 +127,7 @@ func (decoder *decoder) Decode(packet *C.AVPacket) (pkt *Packet, err error) {
 				err = fmt.Errorf("ffmpeg: rtsp_avcodec_encode_wav failed: %d", cerr)
 				return
 			}
-
-			pkt.data = make([]byte, int(encPacket.size))
-			copy(pkt.data, *(*[]byte)(unsafe.Pointer(&encPacket.data)))
+			pkt.data = decodeAVPacket(&encPacket)
 
 		case C.AV_SAMPLE_FMT_S32:
 			if decoder.swrContext == nil {
@@ -153,8 +159,8 @@ func (decoder *decoder) Decode(packet *C.AVPacket) (pkt *Packet, err error) {
 				err = fmt.Errorf("ffmpeg: rtsp_avcodec_encode_resample_wav failed: %d", cerr)
 				return
 			}
-			pkt.data = make([]byte, int(encPacket.size))
-			copy(pkt.data, *(*[]byte)(unsafe.Pointer(&encPacket.data)))
+			pkt.data = decodeAVPacket(&encPacket)
+
 		default:
 			err = fmt.Errorf("ffmpeg: audio format %d not supported: %d", frame.format)
 			return
diff --git a/doc.go b/doc.go
new file mode 100644
index 0000000..d608818
--- /dev/null
+++ b/doc.go
@@ -0,0 +1,3 @@
+// Package go-rtsp is a Golang audio/video library based on FFmpeg.
+// go-rtsp is powerful library to help convert streams/files to jpeg/wav.
+package rtsp
diff --git a/pkt.go b/pkt.go
index c255614..dc9b775 100644
--- a/pkt.go
+++ b/pkt.go
@@ -3,57 +3,68 @@ package rtsp
 // #include "ffmpeg.h"
 import "C"
 
-type Packet struct {
-	streamIndex int
-	codecType   int
-	data        []byte
-
+type Image struct {
 	// only image
-	width  int
-	height int
+	width    int
+	height   int
+	keyFrame bool
+}
 
+// Height if image or 0 if audio
+func (image *Image) Height() int {
+	return image.height
+}
+
+// Width if image or 0 if audio
+func (image *Image) Width() int {
+	return image.width
+}
+
+type Audio struct {
 	// only audio
 	sampleRate int
 	bitRate    int
 	channels   int
 }
 
-// Height if image or 0 if audio
-func (pkt *Packet) Height() int {
-	return pkt.height
-}
-
-// Width if image or 0 if audio
-func (pkt *Packet) Width() int {
-	return pkt.width
-}
-
 // SampleRate if audio or 0 if image
-func (pkt *Packet) SampleRate() int {
-	return pkt.sampleRate
+func (audio *Audio) SampleRate() int {
+	return audio.sampleRate
 }
 
 // BitRate if audio or 0 if image
-func (pkt *Packet) BitRate() int {
-	return pkt.bitRate
+func (audio *Audio) BitRate() int {
+	return audio.bitRate
 }
 
-// BitRate if audio or 0 if image
-func (pkt *Packet) Channels() int {
-	return pkt.channels
+// Channels if audio or 0 if image
+func (audio *Audio) Channels() int {
+	return audio.channels
+}
+
+type Packet struct {
+	streamIndex int
+	codecType   int
+	data        []byte
+
+	duration int64
+	position int64
+
+	Image
+	Audio
 }
 
 // Data encoded jpeg if image or wav if audio
-func (pkt *Packet) Data() []byte {
-	return pkt.data
+func (packet *Packet) Data() []byte {
+	return packet.data
 }
 
 // IsAudio packet
-func (pkt *Packet) IsAudio() bool {
-	return pkt.codecType == C.AVMEDIA_TYPE_AUDIO
+func (packet *Packet) IsAudio() bool {
+	return packet.codecType == C.AVMEDIA_TYPE_AUDIO
 }
 
 // IsVideo packet
-func (pkt *Packet) IsVideo() bool {
-	return pkt.codecType == C.AVMEDIA_TYPE_VIDEO
+func (packet *Packet) IsVideo() bool {
+	return packet.codecType == C.AVMEDIA_TYPE_VIDEO
 }