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Add fragment duration handling and improve MP4 segment management

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This commit is contained in:
Cédric Verstraeten
2026-02-10 13:52:58 +00:00
parent 176610a694
commit 2868ddc499
1 changed files with 84 additions and 58 deletions
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142
machinery/src/video/mp4.go
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@@ -22,6 +22,11 @@ import (
var LastPTS uint64 = 0 // Last PTS for the current segment
// FragmentDurationMs is the target duration for each fragment in milliseconds.
// Fragments will be flushed at the first keyframe after this duration has elapsed,
// resulting in ~3 second fragments (assuming a typical GOP interval).
const FragmentDurationMs = 3000
type MP4 struct {
// FileName is the name of the file
FileName string
@@ -44,6 +49,7 @@ type MP4 struct {
PPSNALUs [][]byte // PPS NALUs for H264
VPSNALUs [][]byte // VPS NALUs for H264
FreeBoxSize int64
FragmentStartPTS uint64 // PTS at the start of the current fragment
MoofBoxes int64 // Number of moof boxes in the file
MoofBoxSizes []int64 // Sizes of each moof box
StartTime uint64 // Start time of the MP4 file
@@ -61,13 +67,12 @@ type MP4 struct {
// NewMP4 creates a new MP4 object
func NewMP4(fileName string, spsNALUs [][]byte, ppsNALUs [][]byte, vpsNALUs [][]byte) *MP4 {
init := mp4ff.NewMP4Init()
// Add a free box to the init segment
// Prepend a free box to the init segment with a size of 4096 bytes, so we can overwrite it later with the actual init segment.
freeBoxSize := 4096
// Reserve space at the start of the file for the ftyp + moov boxes.
// We write a free box as a placeholder that will be overwritten at close
// with the actual init segment. 8KB is generous enough for ftyp + moov
// with video + audio tracks, mvex, and a UUID signature box.
freeBoxSize := 8192
free := mp4ff.NewFreeBox(make([]byte, freeBoxSize))
init.AddChild(free)
// Create a writer
ofd, err := os.Create(fileName)
@@ -77,16 +82,15 @@ func NewMP4(fileName string, spsNALUs [][]byte, ppsNALUs [][]byte, vpsNALUs [][]
// Create a buffered writer
bufferedWriter := bufio.NewWriterSize(ofd, 64*1024) // 64KB buffer
// We will write the empty init segment to the file
// so we can overwrite it later with the actual init segment.
err = init.Encode(bufferedWriter)
// Write the free box placeholder at the start of the file
err = free.Encode(bufferedWriter)
if err != nil {
}
return &MP4{
FileName: fileName,
StartTime: uint64(time.Now().Unix()),
FreeBoxSize: int64(freeBoxSize),
FreeBoxSize: int64(freeBoxSize) + 8, // payload + 8 byte box header
FileWriter: ofd,
Writer: bufferedWriter,
SPSNALUs: spsNALUs,
@@ -134,38 +138,50 @@ func (mp4 *MP4) AddSampleToTrack(trackID uint32, isKeyframe bool, data []byte, p
if isKeyframe {
// Write the segment to the file
// Determine whether to start a new fragment.
// We only flush at a keyframe boundary once at least FragmentDurationMs
// of content has been accumulated, resulting in ~3 second fragments.
elapsed := uint64(0)
if mp4.Start {
mp4.MoofBoxes = mp4.MoofBoxes + 1
mp4.MoofBoxSizes = append(mp4.MoofBoxSizes, int64(mp4.Segment.Size()))
err := mp4.Segment.Encode(mp4.Writer)
if err != nil {
log.Log.Error("mp4.AddSampleToTrack(): error encoding segment: " + err.Error())
elapsed = pts - mp4.FragmentStartPTS
}
shouldFlush := !mp4.Start || elapsed >= FragmentDurationMs
if shouldFlush {
// Write the previous segment to the file
if mp4.Start {
mp4.MoofBoxes = mp4.MoofBoxes + 1
mp4.MoofBoxSizes = append(mp4.MoofBoxSizes, int64(mp4.Segment.Size()))
err := mp4.Segment.Encode(mp4.Writer)
if err != nil {
log.Log.Error("mp4.AddSampleToTrack(): error encoding segment: " + err.Error())
}
mp4.Segments = append(mp4.Segments, mp4.Segment)
}
mp4.Segments = append(mp4.Segments, mp4.Segment)
mp4.Start = true
// Increment the segment count
mp4.SegmentCount = mp4.SegmentCount + 1
// Create a new media segment
seg := mp4ff.NewMediaSegment()
// Create a video fragment
multiTrackFragment, err := mp4ff.CreateMultiTrackFragment(uint32(mp4.SegmentCount), mp4.TrackIDs)
if err != nil {
log.Log.Error("mp4.AddSampleToTrack(): error creating multi track fragment: " + err.Error())
}
mp4.MultiTrackFragment = multiTrackFragment
seg.AddFragment(multiTrackFragment)
// Set to MP4 struct
mp4.Segment = seg
// Set the start PTS for the next segment
mp4.StartPTS = pts
mp4.FragmentStartPTS = pts
}
mp4.Start = true
// Increment the segment count
mp4.SegmentCount = mp4.SegmentCount + 1
// Create a new media segment
seg := mp4ff.NewMediaSegment()
// Create a video fragment
multiTrackFragment, err := mp4ff.CreateMultiTrackFragment(uint32(mp4.SegmentCount), mp4.TrackIDs) // Assuming 1 for video track and 2 for audio track
if err != nil {
log.Log.Error("mp4.AddSampleToTrack(): error creating multi track fragment: " + err.Error())
}
mp4.MultiTrackFragment = multiTrackFragment
seg.AddFragment(multiTrackFragment)
// Set to MP4 struct
mp4.Segment = seg
// Set the start PTS for the next segment
mp4.StartPTS = pts
}
if mp4.Start {
@@ -313,14 +329,14 @@ func (mp4 *MP4) Close(config *models.Config) {
}
mp4.Writer.Flush()
// Ensure all data is written to disk
// Ensure all segment data is on disk before we overwrite the placeholder at offset 0.
if err := mp4.FileWriter.Sync(); err != nil {
log.Log.Error("mp4.Close(): error syncing file: " + err.Error())
}
defer mp4.FileWriter.Close()
// Now we have all the moof and mdat boxes written to the file.
// We can now generate the ftyp and moov boxes, and replace it with the free box we added earlier (size of 2048 bytes).
// We build the ftyp + moov init segment and write it at the start,
// overwriting the free box placeholder we reserved in NewMP4.
init := mp4ff.NewMP4Init()
// Create a new ftyp box
@@ -498,30 +514,40 @@ func (mp4 *MP4) Close(config *models.Config) {
// Add the SIDX box to the moov box
init.AddChild(sidx)*/
// Get a bit slice writer for the init segment
// Get a byte buffer of FreeBoxSize bytes to write the init segment
buffer := bytes.NewBuffer(make([]byte, 0))
init.Encode(buffer)
// The first FreeBoxSize bytes of the file is a free box, so we can read it and replace it with the moov box.
// The init box might not be FreeBoxSize bytes, so we need to read the first FreeBoxSize bytes and then replace it with the moov box.
// while the remaining bytes are for a new free box.
// Write the init segment at the beginning of the file, replacing the free box
if _, err := mp4.FileWriter.WriteAt(buffer.Bytes(), 0); err != nil {
// Encode the ftyp + moov init segment into a buffer so we know its size.
var initBuf bytes.Buffer
if err := init.Encode(&initBuf); err != nil {
log.Log.Error("mp4.Close(): error encoding init segment: " + err.Error())
}
// Calculate the remaining size for the free box
remainingSize := mp4.FreeBoxSize - int64(buffer.Len())
if remainingSize > 0 {
newFreeBox := mp4ff.NewFreeBox(make([]byte, remainingSize))
initSize := int64(initBuf.Len())
if initSize > mp4.FreeBoxSize {
log.Log.Error(fmt.Sprintf("mp4.Close(): init segment (%d bytes) exceeds reserved space (%d bytes), file may be corrupt", initSize, mp4.FreeBoxSize))
}
// Write the init segment at the beginning of the file, overwriting the free box placeholder.
if _, err := mp4.FileWriter.WriteAt(initBuf.Bytes(), 0); err != nil {
log.Log.Error("mp4.Close(): error writing init segment: " + err.Error())
}
// Fill any remaining reserved space with a new (smaller) free box so
// the byte offsets of the moof/mdat boxes that follow are preserved.
remainingSize := mp4.FreeBoxSize - initSize
if remainingSize >= 8 { // minimum box size is 8 bytes (header only)
newFree := mp4ff.NewFreeBox(make([]byte, remainingSize-8))
var freeBuf bytes.Buffer
if err := newFreeBox.Encode(&freeBuf); err != nil {
if err := newFree.Encode(&freeBuf); err != nil {
log.Log.Error("mp4.Close(): error encoding free box: " + err.Error())
}
if _, err := mp4.FileWriter.WriteAt(freeBuf.Bytes(), int64(buffer.Len())); err != nil {
if _, err := mp4.FileWriter.WriteAt(freeBuf.Bytes(), initSize); err != nil {
log.Log.Error("mp4.Close(): error writing free box: " + err.Error())
}
}
if err := mp4.FileWriter.Sync(); err != nil {
log.Log.Error("mp4.Close(): error syncing file: " + err.Error())
}
mp4.FileWriter.Close()
}
type segData struct {