diff --git a/mp4/av1c_test.go b/mp4/av1c_test.go
new file mode 100644
index 00000000..4ec9b417
--- /dev/null
+++ b/mp4/av1c_test.go
@@ -0,0 +1,18 @@
+package mp4
+
+import (
+	"testing"
+
+	"github.com/Eyevinn/mp4ff/av1"
+)
+
+func TestEncodeDecodeAvc1(t *testing.T) {
+	adc := Av1CBox{
+		CodecConfRec: av1.CodecConfRec{
+			Version: 1,
+		},
+	}
+
+	boxDiffAfterEncodeAndDecode(t, &adc)
+
+}
diff --git a/mp4/cdat_test.go b/mp4/cdat_test.go
new file mode 100644
index 00000000..581da22c
--- /dev/null
+++ b/mp4/cdat_test.go
@@ -0,0 +1,11 @@
+package mp4
+
+import "testing"
+
+func TestEncodeDecodeCdat(t *testing.T) {
+
+	cdat := CdatBox{
+		Data: []byte{0x01, 0x02, 0x03, 0x04},
+	}
+	boxDiffAfterEncodeAndDecode(t, &cdat)
+}
diff --git a/mp4/ffmpeg_test.go b/mp4/ffmpeg_test.go
index c049216f..7508b400 100644
--- a/mp4/ffmpeg_test.go
+++ b/mp4/ffmpeg_test.go
@@ -14,8 +14,8 @@ func TestDecodeFFMpeg(t *testing.T) {
 	if err != nil {
 		t.Error(err)
 	}
-	sr := bits.NewFixedSliceReader(raw)
-	box, err := DecodeBoxSR(0, sr)
+	buf := bytes.NewBuffer(raw)
+	box, err := DecodeBox(0, buf)
 	if err != nil {
 		t.Error(err)
 	}
@@ -29,5 +29,10 @@ func TestDecodeFFMpeg(t *testing.T) {
 	if !bytes.Equal(raw, encBytes) {
 		t.Errorf("encoded ffmpeg boxes not same as input")
 	}
+}
 
+func TestEncodeData(t *testing.T) {
+	data := []byte("dummy")
+	db := &DataBox{Data: data}
+	boxDiffAfterEncodeAndDecode(t, db)
 }
diff --git a/mp4/mfhd_test.go b/mp4/mfhd_test.go
new file mode 100644
index 00000000..3d86a691
--- /dev/null
+++ b/mp4/mfhd_test.go
@@ -0,0 +1,12 @@
+package mp4
+
+import "testing"
+
+func TestEncodeDecodeMfhd(t *testing.T) {
+	mfhd := &MfhdBox{
+		Version:        0,
+		Flags:          0,
+		SequenceNumber: 1,
+	}
+	boxDiffAfterEncodeAndDecode(t, mfhd)
+}
diff --git a/mp4/sample_test.go b/mp4/sample_test.go
new file mode 100644
index 00000000..31099922
--- /dev/null
+++ b/mp4/sample_test.go
@@ -0,0 +1,20 @@
+package mp4
+
+import (
+	"testing"
+)
+
+func TestSample(t *testing.T) {
+	s := NewSample(SyncSampleFlags, 1000, 100, -1001)
+	fs := FullSample{
+		Sample:     s,
+		DecodeTime: 1000,
+		Data:       []byte{0x01, 0x02, 0x03, 0x04},
+	}
+	if !s.IsSync() {
+		t.Error("Expected sync sample")
+	}
+	if fs.PresentationTime() != 0 {
+		t.Error("Expected presentation time 0")
+	}
+}
diff --git a/mp4/stsd_test.go b/mp4/stsd_test.go
new file mode 100644
index 00000000..db8fad53
--- /dev/null
+++ b/mp4/stsd_test.go
@@ -0,0 +1,52 @@
+package mp4
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/Eyevinn/mp4ff/aac"
+)
+
+func TestStsd(t *testing.T) {
+	stsd := StsdBox{}
+	samplingFrequency := 48000
+	asc := &aac.AudioSpecificConfig{
+		ObjectType:           2,
+		ChannelConfiguration: 2,
+		SamplingFrequency:    samplingFrequency,
+		ExtensionFrequency:   0,
+		SBRPresentFlag:       false,
+		PSPresentFlag:        false,
+	}
+	buf := &bytes.Buffer{}
+	err := asc.Encode(buf)
+	if err != nil {
+		t.Error(err)
+	}
+	ascBytes := buf.Bytes()
+	esds := CreateEsdsBox(ascBytes)
+	mp4a := CreateAudioSampleEntryBox("mp4a",
+		uint16(asc.ChannelConfiguration),
+		16, uint16(samplingFrequency), esds)
+	btrt := BtrtBox{
+		BufferSizeDB: 1536,
+		MaxBitrate:   96000,
+		AvgBitrate:   96000,
+	}
+	mp4a.AddChild(&btrt)
+	stsd.AddChild(mp4a)
+	if len(stsd.Children) != 1 {
+		t.Error("Expected one child")
+	}
+	if stsd.Mp4a == nil {
+		t.Error("Expected mp4a child")
+	}
+	gb := stsd.GetBtrt()
+	if gb == nil {
+		t.Error("Expected btrt")
+	} else {
+		if *gb != btrt {
+			t.Errorf("Got btrt %v, expected %v", *gb, btrt)
+		}
+	}
+}
diff --git a/mp4/trak.go b/mp4/trak.go
index 5eb7f142..9d4a1ae9 100644
--- a/mp4/trak.go
+++ b/mp4/trak.go
@@ -121,7 +121,7 @@ func (t *TrakBox) GetSampleData(startSampleNr, endSampleNr uint32) ([]Sample, er
 		if ctts != nil {
 			cto = ctts.GetCompositionTimeOffset(nr)
 		}
-		samples[nr] = Sample{
+		samples[nr-1] = Sample{
 			Flags:                 createSampleFlagsFromProgressiveBoxes(stss, sdtp, nr),
 			Dur:                   stts.GetDur(nr),
 			Size:                  stbl.Stsz.GetSampleSize(int(nr)),
diff --git a/mp4/trak_test.go b/mp4/trak_test.go
new file mode 100644
index 00000000..b9a4d941
--- /dev/null
+++ b/mp4/trak_test.go
@@ -0,0 +1,42 @@
+package mp4
+
+import (
+	"os"
+	"testing"
+)
+
+func TestTrakSampleFunctions(t *testing.T) {
+	testFile := "testdata/bbb_prog_10s.mp4"
+	f, err := os.Open(testFile)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+	mf, err := DecodeFile(f)
+	if err != nil {
+		t.Fatal(err)
+	}
+	moov := mf.Moov
+	traks := moov.Traks
+	if len(traks) != 2 {
+		t.Fatalf("expected 2 tracks, got %d", len(traks))
+	}
+	trak := traks[0]
+	if trak.Tkhd.TrackID != 1 {
+		t.Fatalf("expected trackID 1, got %d", trak.Tkhd.TrackID)
+	}
+	first2Samples, err := trak.GetSampleData(1, 2)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(first2Samples) != 2 {
+		t.Fatalf("expected 2 samples, got %d", len(first2Samples))
+	}
+	ranges, err := trak.GetRangesForSampleInterval(1, 2)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(ranges) != 1 {
+		t.Fatalf("expected 1 range, got %d", len(ranges))
+	}
+}
diff --git a/mp4/version_test.go b/mp4/version_test.go
new file mode 100644
index 00000000..26dd3949
--- /dev/null
+++ b/mp4/version_test.go
@@ -0,0 +1,8 @@
+package mp4
+
+import "fmt"
+
+func ExampleGetVersion() {
+	fmt.Println(GetVersion())
+	// Output: v0.46, date: 2024-08-08
+}
diff --git a/sei/sei5.go b/sei/sei5.go
index 168594a6..2fb0a528 100644
--- a/sei/sei5.go
+++ b/sei/sei5.go
@@ -8,7 +8,7 @@ import (
 // UnregisteredSEI is SEI message of type 5.
 type UnregisteredSEI struct {
 	UUID    []byte
-	payload []byte
+	payload []byte // raw rbsp payload including UUID
 }
 
 // Type returns SEI payload type.
diff --git a/sei/sei5_test.go b/sei/sei5_test.go
new file mode 100644
index 00000000..cd4f3187
--- /dev/null
+++ b/sei/sei5_test.go
@@ -0,0 +1,31 @@
+package sei
+
+import (
+	"testing"
+)
+
+func TestSEI5_UnregisteredType(t *testing.T) {
+	raw := []byte{0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+		0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
+		0x40, 0x40, 0x40, 0x40}
+
+	us, err := DecodeUserDataUnregisteredSEI(&SEIData{payloadType: SEIUserDataUnregisteredType,
+		payload: raw})
+	if err != nil {
+		t.Error("Error decoding SEIUserDataUnregisteredType")
+	}
+	if us.Type() != SEIUserDataUnregisteredType {
+		t.Error("Expected SEIUserDataUnregisteredType")
+	}
+	if us.Size() != 20 {
+		t.Errorf("Expected size 20, got %d", us.Size())
+	}
+	if string(us.Payload()) != string(raw) {
+		t.Errorf("Unexpected payload %v, expected %v", us.Payload(), raw)
+	}
+	wantedString := "SEI type 5, size=20, uuid=\"000102030405060708090a0b0c0d0e0f\", payload=\"@@@@\""
+	if wantedString != us.String() {
+		t.Errorf("Unexpected string %q, expected %q", us.String(), wantedString)
+	}
+
+}