mp4: Properly use trun data offset

Each trun has it's own data offset, before the last offset was wrongly used
for all truns. Could also cause sample ranges to be beyond EOF.

tenc: Decode default constant iv

Fixes #292

format/mp4/boxes.go

@@ -196,8 +196,9 @@ type moofBox struct {
 }
 
 type trafBox struct {
-	trackID int
-	moof    *moof
+	trackID        int
+	baseDataOffset int64
+	moof           *moof
 }
 
 func irefEntryDecode(ctx *decodeContext, d *decode.D) {
@@ -777,7 +778,8 @@ func init() {
 		},
 		"moov": decodeBoxes,
 		"moof": func(ctx *decodeContext, d *decode.D) {
-			decodeBoxesWithParentData(ctx, d, &moofBox{offset: (d.Pos() / 8) - 8})
+			offset := (d.Pos() / 8) - 8
+			decodeBoxesWithParentData(ctx, d, &moofBox{offset: offset})
 		},
 		// Track Fragment
 		"traf": func(ctx *decodeContext, d *decode.D) {
@@ -807,7 +809,6 @@ func init() {
 				d.FieldU1("unused2")
 				sampleDescriptionIndexPresent = d.FieldBool("sample_description_index_present")
 				baseDataOffsetPresent = d.FieldBool("base_data_offset_present")
-
 			})
 			trackID := int(d.FieldU32("track_id"))
 
@@ -815,16 +816,10 @@ func init() {
 			if mb := ctx.currentMoofBox(); mb != nil {
 				m.offset = mb.offset
 			}
-			if t := ctx.currentTrafBox(); t != nil {
-				t.trackID = trackID
-				t.moof = m
-			}
-			if t := ctx.currentTrack(); t != nil {
-				t.moofs = append(t.moofs, m)
-			}
 
+			baseDataOffset := int64(0)
 			if baseDataOffsetPresent {
-				d.FieldU64("base_data_offset")
+				baseDataOffset = int64(d.FieldU64("base_data_offset"))
 			}
 			if sampleDescriptionIndexPresent {
 				m.defaultSampleDescriptionIndex = int(d.FieldU32("sample_description_index"))
@@ -838,6 +833,15 @@ func init() {
 			if defaultSampleFlagsPresent {
 				d.FieldU32("default_sample_flags")
 			}
+
+			if t := ctx.currentTrafBox(); t != nil {
+				t.trackID = trackID
+				t.moof = m
+				t.baseDataOffset = baseDataOffset
+			}
+			if t := ctx.currentTrack(); t != nil {
+				t.moofs = append(t.moofs, m)
+			}
 		},
 		// Track Fragment Run
 		"trun": func(ctx *decodeContext, d *decode.D) {
@@ -865,8 +869,9 @@ func init() {
 				dataOffsetPresent = d.FieldBool("data_offset_present")
 			})
 			sampleCount := d.FieldU32("sample_count")
+			dataOffset := int64(0)
 			if dataOffsetPresent {
-				m.dataOffset = d.FieldS32("data_offset")
+				dataOffset = d.FieldS32("data_offset")
 			}
 			if firstSampleFlagsPresent {
 				d.FieldU32("first_sample_flags")
@@ -876,6 +881,9 @@ func init() {
 				d.Errorf("too many sample trun entries %d > %d", sampleCount, maxSampleEntryCount)
 			}
 
+			t := trun{
+				dataOffset: dataOffset,
+			}
 			d.FieldArray("samples", func(d *decode.D) {
 				for i := uint64(0); i < sampleCount; i++ {
 					sampleSize := m.defaultSampleSize
@@ -894,9 +902,11 @@ func init() {
 						}
 					})
 
-					m.samplesSizes = append(m.samplesSizes, sampleSize)
+					t.samplesSizes = append(t.samplesSizes, sampleSize)
 				}
 			})
+
+			m.truns = append(m.truns, t)
 		},
 		"tfdt": func(_ *decodeContext, d *decode.D) {
 			version := d.FieldU8("version")
@@ -1244,7 +1254,9 @@ func init() {
 			d.FieldArray("samples", func(d *decode.D) {
 				for i := uint64(0); i < sampleCount; i++ {
 					d.FieldStruct("entry", func(d *decode.D) {
-						d.FieldRawLen("iv", int64(t.defaultIVSize*8))
+						if t.defaultIVSize != 0 {
+							d.FieldRawLen("iv", int64(t.defaultIVSize*8))
+						}
 						if flags&0b10 != 0 {
 							subSampleCount := d.FieldU16("subsample_count")
 							d.FieldArray("subsamples", func(d *decode.D) {
@@ -1278,7 +1290,8 @@ func init() {
 			d.FieldRawLen("default_kid", 8*16)
 
 			if defaultIsEncrypted != 0 && defaultIVSize == 0 {
-				d.FieldU8("default_constant_iv_size")
+				defaultConstantIVSize := d.FieldU8("default_constant_iv_size")
+				d.FieldRawLen("default_constant_iv", int64(defaultConstantIVSize)*8)
 			}
 			if t := ctx.currentTrack(); t != nil {
 				t.defaultIVSize = int(defaultIVSize)

format/mp4/mp4.go

@@ -102,8 +102,12 @@ type moof struct {
 	offset                        int64
 	defaultSampleSize             int64
 	defaultSampleDescriptionIndex int
-	dataOffset                    int64
-	samplesSizes                  []int64
+	truns                         []trun
+}
+
+type trun struct {
+	dataOffset   int64
+	samplesSizes []int64
 }
 
 type sampleDescription struct {
@@ -339,20 +343,39 @@ func mp4Tracks(d *decode.D, ctx *decodeContext) {
 						}
 					}
 
+					sampleNr := 0
 					for _, m := range t.moofs {
-						sampleOffset := m.offset + m.dataOffset
-						for _, sz := range m.samplesSizes {
-							dataFormat := trackSDDataFormat
-							if m.defaultSampleDescriptionIndex != 0 && m.defaultSampleDescriptionIndex-1 < len(t.sampleDescriptions) {
-								sd := t.sampleDescriptions[m.defaultSampleDescriptionIndex-1]
-								dataFormat = sd.dataFormat
-								if sd.originalFormat != "" {
-									dataFormat = sd.originalFormat
-								}
-							}
+						for _, trun := range m.truns {
+							sampleOffset := m.offset + trun.dataOffset
 
-							decodeSampleRange(d, t, dataFormat, "sample", sampleOffset*8, sz*8, t.formatInArg)
-							sampleOffset += sz
+							for _, sz := range trun.samplesSizes {
+								dataFormat := trackSDDataFormat
+								if m.defaultSampleDescriptionIndex != 0 && m.defaultSampleDescriptionIndex-1 < len(t.sampleDescriptions) {
+									sd := t.sampleDescriptions[m.defaultSampleDescriptionIndex-1]
+									dataFormat = sd.dataFormat
+									if sd.originalFormat != "" {
+										dataFormat = sd.originalFormat
+									}
+								}
+
+								// logStrFn := func() string {
+								// 	return fmt.Sprintf("%d: %s: %d: (%s): sz=%d %d+%d=%d",
+								// 		t.id,
+								// 		dataFormat,
+								// 		sampleNr,
+								// 		trackSDDataFormat,
+								// 		sz,
+								// 		m.offset,
+								// 		m.dataOffset,
+								// 		sampleOffset,
+								// 	)
+								// }
+								// log.Println(logStrFn())
+
+								decodeSampleRange(d, t, dataFormat, "sample", sampleOffset*8, sz*8, t.formatInArg)
+								sampleOffset += sz
+								sampleNr++
+							}
 						}
 					}
 				})