convert Tracks into Medias and Formats (#155)

* split tracks from medias

* move tracks into dedicated package

* move media into dedicated package

* edit Medias.Marshal() in order to return SDP

* add medias.Find() and simplify examples

* improve coverage

* fix rebase errors

* replace TrackIDs with MediaIDs

* implement media-specific and track-specific callbacks for reading RTCP and RTP packets

* rename publish into record, read into play

* add v2 tag

* rename tracks into formats

pkg/format/mpeg4audio_test.go

@@ -0,0 +1,63 @@
+package format
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/aler9/gortsplib/v2/pkg/mpeg4audio"
+)
+
+func TestMPEG4AudioAttributes(t *testing.T) {
+	format := &MPEG4Audio{
+		PayloadTyp: 96,
+		Config: &mpeg4audio.Config{
+			Type:         mpeg4audio.ObjectTypeAACLC,
+			SampleRate:   48000,
+			ChannelCount: 2,
+		},
+		SizeLength:       13,
+		IndexLength:      3,
+		IndexDeltaLength: 3,
+	}
+	require.Equal(t, "MPEG4-audio", format.String())
+	require.Equal(t, 48000, format.ClockRate())
+	require.Equal(t, uint8(96), format.PayloadType())
+}
+
+func TestMPEG4AudioClone(t *testing.T) {
+	format := &MPEG4Audio{
+		PayloadTyp: 96,
+		Config: &mpeg4audio.Config{
+			Type:         mpeg4audio.ObjectTypeAACLC,
+			SampleRate:   48000,
+			ChannelCount: 2,
+		},
+		SizeLength:       13,
+		IndexLength:      3,
+		IndexDeltaLength: 3,
+	}
+
+	clone := format.Clone()
+	require.NotSame(t, format, clone)
+	require.Equal(t, format, clone)
+}
+
+func TestMPEG4AudioMediaDescription(t *testing.T) {
+	format := &MPEG4Audio{
+		PayloadTyp: 96,
+		Config: &mpeg4audio.Config{
+			Type:         mpeg4audio.ObjectTypeAACLC,
+			SampleRate:   48000,
+			ChannelCount: 2,
+		},
+		SizeLength:       13,
+		IndexLength:      3,
+		IndexDeltaLength: 3,
+	}
+
+	rtpmap, fmtp := format.Marshal()
+	require.Equal(t, "mpeg4-generic/48000/2", rtpmap)
+	require.Equal(t, "profile-level-id=1; mode=AAC-hbr; sizelength=13;"+
+		" indexlength=3; indexdeltalength=3; config=1190", fmtp)
+}