container/mts: filled Clip.Bytes

writing Clip.Bytes required a change to the Clip type. The Clip type now possess a slice that
references the memory in which the Frames should reference for the media. Appropriate changes have
been made to Extract and TestExtract to accomidate this change.

container/mts/payload.go

@@ -8,18 +8,16 @@ import (
 )
 
 // Extract extracts the media from an MPEG-TS clip given by p.
-func Extract(p []byte) (Clip, error) {
+func Extract(p []byte) (*Clip, error) {
 	l := len(p)
 	// Check that clip is divisible by 188, i.e. contains a series of full MPEG-TS clips.
 	if l%PacketSize != 0 {
 		return nil, errors.New("MTS clip is not of valid size")
 	}
 
-	// This will hold a copy of all the media in the MPEG-TS clip.
-	buf := make([]byte, 0, l/PacketSize)
-
 	var (
-		clip        Clip              // The data that will be returned.
+		frameStart  int               // Index used to indicate the start of current frame in backing slice.
+		clip        = &Clip{}         // The data that will be returned.
 		meta        map[string]string // Holds the most recently extracted meta.
 		lenOfFrame  int               // Len of current frame.
 		dataLen     int               // Len of data from MPEG-TS packet.
@@ -29,6 +27,9 @@ func Extract(p []byte) (Clip, error) {
 		err         error
 	)
 
+	// This will hold a copy of all the media in the MPEG-TS clip.
+	clip.backing = make([]byte, 0, l/PacketSize)
+
 	// Go through the MPEGT-TS packets.
 	var pkt packet.Packet
 	for i := 0; i < l; i += PacketSize {
@@ -61,40 +62,42 @@ func Extract(p []byte) (Clip, error) {
 				// Extract the PTS and ID, then add a new frame to the clip.
 				curPTS = _pes.PTS()
 				curStreamID = _pes.StreamId()
-				clip = append(clip, Frame{
+				clip.frames = append(clip.frames, Frame{
 					PTS:  curPTS,
 					ID:   curStreamID,
 					Meta: meta,
 				})
 
 				// Append the data to the underlying buffer and get appended lenghth.
-				buf = append(buf, _pes.Data()...)
+				clip.backing = append(clip.backing, _pes.Data()...)
 				dataLen = len(_pes.Data())
 
 				// If we haven't hit the first PUSI, then we know we have a full frame
 				// and can add this data to the frame pertaining to the finish frame.
 				if !firstPUSI {
-					clip[len(clip)-2].Media = buf[:lenOfFrame]
-					buf = buf[lenOfFrame:]
-					lenOfFrame = 0
+					clip.frames[len(clip.frames)-2].Media = clip.backing[frameStart:lenOfFrame]
+					frameStart = lenOfFrame
 				}
 				firstPUSI = false
 			} else {
 				// We're not at the start of the frame, so we don't have a PES header.
 				// We can append the MPEG-TS data directly to the underlying buf.
 				dataLen = len(payload)
-				buf = append(buf, payload...)
+				clip.backing = append(clip.backing, payload...)
 			}
 			lenOfFrame += dataLen
 		}
 	}
 	// We're finished up with media frames, so give the final Frame it's data.
-	clip[len(clip)-1].Media = buf[:lenOfFrame]
+	clip.frames[len(clip.frames)-1].Media = clip.backing[frameStart:lenOfFrame]
 	return clip, nil
 }
 
 // Clip represents a clip of media, i.e. a sequence of media frames.
-type Clip []Frame
+type Clip struct {
+	frames  []Frame
+	backing []byte
+}
 
 // Frame describes a media frame that may be extracted from a PES packet.
 type Frame struct {
@@ -106,5 +109,8 @@ type Frame struct {
 
 // Bytes returns the concatentated media bytes from each frame in the Clip c.
 func (c *Clip) Bytes() []byte {
-	return nil
+	if c.backing == nil {
+		panic("the clip backing array cannot be nil")
+	}
+	return c.backing
 }

container/mts/payload_test.go

@@ -73,7 +73,7 @@ func TestExtract(t *testing.T) {
 		}
 
 		// Create an equivalent Frame and append to our Clip want.
-		want = append(want, Frame{
+		want.frames = append(want.frames, Frame{
 			Media: frame,
 			PTS:   nextPTS,
 			ID:    H264ID,
@@ -88,14 +88,14 @@ func TestExtract(t *testing.T) {
 	}
 
 	// Check length of got and want.
-	if len(want) != len(got) {
-		t.Fatalf("did not get expected length for got.\nGot: %v\n, Want: %v\n", len(got), len(want))
+	if len(want.frames) != len(got.frames) {
+		t.Fatalf("did not get expected length for got.\nGot: %v\n, Want: %v\n", len(got.frames), len(want.frames))
 	}
 
 	// Check frames individually.
-	for i, frame := range want {
-		if !reflect.DeepEqual(frame, got[i]) {
-			t.Fatalf("did not get expected result.\nGot: %v\n, Want: %v\n", got[i], frame)
+	for i, frame := range want.frames {
+		if !reflect.DeepEqual(frame, got.frames[i]) {
+			t.Fatalf("did not get expected result.\nGot: %v\n, Want: %v\n", got.frames[i], frame)
 		}
 	}
 }