muxer: keep TARGETDURATION constant to minimize iOS errors (#187)

muxer.go

@@ -5,13 +5,12 @@ import (
 	"encoding/hex"
 	"fmt"
 	"io"
+	"log"
 	"net/http"
 	"strconv"
 	"sync"
 	"time"
 
-	"github.com/bluenviron/mediacommon/pkg/formats/fmp4"
-
 	"github.com/bluenviron/gohlslib/v2/pkg/codecs"
 	"github.com/bluenviron/gohlslib/v2/pkg/storage"
 )
@@ -80,11 +79,8 @@ func fmp4TimeScale(c codecs.Codec) uint32 {
 	return 90000
 }
 
-type fmp4AugmentedSample struct {
-	fmp4.PartSample
-	dts time.Duration
-	ntp time.Time
-}
+// MuxerOnEncodeErrorFunc is the prototype of Muxer.OnEncodeError.
+type MuxerOnEncodeErrorFunc func(err error)
 
 // Muxer is a HLS muxer.
 type Muxer struct {
@@ -121,6 +117,12 @@ type Muxer struct {
 	// than saving them on RAM, but allows to preserve RAM.
 	Directory string
 
+	//
+	// callbacks (all optional)
+	//
+	// called when a non-fatal encode error occurs.
+	OnEncodeError MuxerOnEncodeErrorFunc
+
 	//
 	// private
 	//
@@ -157,6 +159,11 @@ func (m *Muxer) Start() error {
 	if m.SegmentMaxSize == 0 {
 		m.SegmentMaxSize = 50 * 1024 * 1024
 	}
+	if m.OnEncodeError == nil {
+		m.OnEncodeError = func(e error) {
+			log.Printf("%v", e)
+		}
+	}
 
 	if len(m.Tracks) == 0 {
 		return fmt.Errorf("at least one track must be provided")

muxer_segmenter.go

@@ -51,6 +51,12 @@ func findCompatiblePartDuration(
 	return i
 }
 
+type fmp4AugmentedSample struct {
+	fmp4.PartSample
+	dts time.Duration
+	ntp time.Time
+}
+
 type muxerSegmenter struct {
 	muxer *Muxer // TODO: remove
 

muxer_server.go

@@ -1,7 +1,6 @@
 package gohlslib
 
 import (
-	"math"
 	"net/http"
 	"net/url"
 	"path/filepath"
@@ -21,50 +20,6 @@ func boolPtr(v bool) *bool {
 	return &v
 }
 
-func targetDuration(segments []muxerSegment) int {
-	ret := int(0)
-
-	// EXTINF, when rounded to the nearest integer, must be <= EXT-X-TARGETDURATION
-	for _, sog := range segments {
-		v := int(math.Round(sog.getDuration().Seconds()))
-		if v > ret {
-			ret = v
-		}
-	}
-
-	return ret
-}
-
-func partTargetDuration(
-	streams []*muxerStream,
-) time.Duration {
-	var ret time.Duration
-
-	for _, stream := range streams {
-		for _, seg := range stream.segments {
-			seg, ok := seg.(*muxerSegmentFMP4)
-			if !ok {
-				continue
-			}
-
-			for _, part := range seg.parts {
-				if part.getDuration() > ret {
-					ret = part.getDuration()
-				}
-			}
-		}
-
-		for _, part := range stream.nextSegment.(*muxerSegmentFMP4).parts {
-			if part.getDuration() > ret {
-				ret = part.getDuration()
-			}
-		}
-	}
-
-	// round to milliseconds to avoid changes, that are illegal on iOS
-	return time.Millisecond * time.Duration(math.Ceil(float64(ret)/float64(time.Millisecond)))
-}
-
 func parseMSNPart(msn string, part string) (uint64, uint64, error) {
 	var msnint uint64
 	if msn != "" {

muxer_stream.go

@@ -1,7 +1,9 @@
 package gohlslib
 
 import (
+	"fmt"
 	"io"
+	"math"
 	"net/http"
 	"net/url"
 	"strconv"
@@ -42,6 +44,49 @@ func containsCodec(cs []string, c string) bool {
 	return false
 }
 
+func targetDuration(segments []muxerSegment) int {
+	ret := int(0)
+
+	// EXTINF, when rounded to the nearest integer, must be <= EXT-X-TARGETDURATION
+	for _, sog := range segments {
+		v := int(math.Round(sog.getDuration().Seconds()))
+		if v > ret {
+			ret = v
+		}
+	}
+
+	return ret
+}
+
+func partTargetDuration(
+	segments []muxerSegment,
+	nextSegmentParts []*muxerPart,
+) time.Duration {
+	var ret time.Duration
+
+	for _, seg := range segments {
+		seg, ok := seg.(*muxerSegmentFMP4)
+		if !ok {
+			continue
+		}
+
+		for _, part := range seg.parts {
+			if part.getDuration() > ret {
+				ret = part.getDuration()
+			}
+		}
+	}
+
+	for _, part := range nextSegmentParts {
+		if part.getDuration() > ret {
+			ret = part.getDuration()
+		}
+	}
+
+	// round to milliseconds to minimize changes
+	return time.Millisecond * time.Duration(math.Ceil(float64(ret)/float64(time.Millisecond)))
+}
+
 type generateMediaPlaylistFunc func(
 	isDeltaUpdate bool,
 	rawQuery string,
@@ -63,6 +108,8 @@ type muxerStream struct {
 	nextSegment            muxerSegment
 	nextPart               *muxerPart // low-latency only
 	initFilePresent        bool       // fmp4 only
+	targetDuration         int
+	partTargetDuration     time.Duration
 }
 
 func (s *muxerStream) initialize() {
@@ -343,7 +390,7 @@ func (s *muxerStream) generateMediaPlaylistMPEGTS(
 	pl := &playlist.Media{
 		Version:        3,
 		AllowCache:     boolPtr(false),
-		TargetDuration: targetDuration(s.segments),
+		TargetDuration: s.targetDuration,
 		MediaSequence:  s.muxer.segmentDeleteCount,
 	}
 
@@ -380,8 +427,7 @@ func (s *muxerStream) generateMediaPlaylistFMP4(
 	}
 
 	if s.muxer.Variant == MuxerVariantLowLatency {
-		partTarget := partTargetDuration(s.muxer.streams)
-		partHoldBack := (partTarget * 25) / 10
+		partHoldBack := (s.partTargetDuration * 25) / 10
 
 		pl.ServerControl = &playlist.MediaServerControl{
 			CanBlockReload: true,
@@ -390,7 +436,7 @@ func (s *muxerStream) generateMediaPlaylistFMP4(
 		}
 
 		pl.PartInf = &playlist.MediaPartInf{
-			PartTarget: partTarget,
+			PartTarget: s.partTargetDuration,
 		}
 	}
 
@@ -619,6 +665,19 @@ func (s *muxerStream) rotateParts(nextDTS time.Duration, createNew bool) error {
 		}
 	}
 
+	// while segment target duration can be increased indefinitely,
+	// part target duration cannot, since
+	// "The duration of a Partial Segment MUST be at least 85% of the Part Target Duration"
+	// so it's better to reset it every time.
+	partTargetDuration := partTargetDuration(s.segments, part.segment.parts)
+	if s.partTargetDuration == 0 {
+		s.partTargetDuration = partTargetDuration
+	} else if partTargetDuration != s.partTargetDuration {
+		s.muxer.OnEncodeError(fmt.Errorf("part duration changed from %v to %v - this will cause an error in iOS clients",
+			s.partTargetDuration, partTargetDuration))
+		s.partTargetDuration = partTargetDuration
+	}
+
 	if createNew {
 		nextPart := &muxerPart{
 			stream:   s,
@@ -710,6 +769,15 @@ func (s *muxerStream) rotateSegments(
 		}
 	}
 
+	targetDuration := targetDuration(s.segments)
+	if s.targetDuration == 0 {
+		s.targetDuration = targetDuration
+	} else if targetDuration > s.targetDuration {
+		s.muxer.OnEncodeError(fmt.Errorf("segment duration changed from %ds to %ds - this will cause an error in iOS clients",
+			s.targetDuration, targetDuration))
+		s.targetDuration = targetDuration
+	}
+
 	// create next segment
 	var nextSegment muxerSegment
 	if s.muxer.Variant == MuxerVariantMPEGTS {