feat: new tool mp4ff-crop to crop progressive mp4 files

README.md

@@ -185,8 +185,11 @@ Some useful command line tools are available in `cmd`.
 2. `mp4ff-pslister` extracts and displays SPS and PPS for AVC in a mp4 file. Partial information is printed for HEVC.
 3. `mp4ff-nallister` lists NALUs and picture types for video in progressive or fragmented file
 4. `mp4ff-wvttlister` lists details of wvtt (WebVTT in ISOBMFF) samples
+5. `mp4ff-crop` shortens a progressive mp4 file to a specified duration
 
-You can install these tools by going to their respective directory and run `go install .`.
+You can install these tools by going to their respective directory and run `go install .` or directly from the repo with
+
+    go install github.com/edgeware/mp4ff/cmd/mp4ff-info@latest
 
 ## Example code
 

cmd/mp4ff-crop/byteranges.go

@@ -0,0 +1,30 @@
+package main
+
+type byteRange struct {
+	start uint64
+	end   uint64 // Included
+}
+
+type byteRanges struct {
+	ranges []byteRange
+}
+
+func createByteRanges() *byteRanges {
+	return &byteRanges{}
+}
+
+func (b *byteRanges) addRange(start, end uint64) {
+	if len(b.ranges) == 0 || b.ranges[len(b.ranges)-1].end+1 != start {
+		b.ranges = append(b.ranges, byteRange{start, end})
+		return
+	}
+	b.ranges[len(b.ranges)-1].end = end
+}
+
+func (b *byteRanges) size() uint64 {
+	var totSize uint64 = 0
+	for _, br := range b.ranges {
+		totSize += br.end - br.start + 1
+	}
+	return uint64(totSize)
+}

cmd/mp4ff-crop/crop_test.go

@@ -0,0 +1,44 @@
+package main
+
+import (
+	"bytes"
+	"log"
+	"os"
+	"testing"
+
+	"github.com/edgeware/mp4ff/mp4"
+)
+
+// TestCroppedFileDuration - simple test to check that cropped file has right duration
+// In general, this duration will not be exactly the same as the one asked for.
+func TestCroppedFileDuration(t *testing.T) {
+	testFile := "../../mp4/testdata/prog_8s.mp4"
+	cropDur := 2000
+
+	ifh, err := os.Open(testFile)
+	if err != nil {
+		t.Error(err)
+	}
+	defer ifh.Close()
+	parsedMp4, err := mp4.DecodeFile(ifh, mp4.WithDecodeMode(mp4.DecModeLazyMdat))
+	if err != nil {
+		t.Error(err)
+	}
+
+	buf := bytes.Buffer{}
+
+	err = cropMP4(parsedMp4, cropDur, &buf, ifh)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	decCropped, err := mp4.DecodeFile(&buf)
+	if err != nil {
+		t.Error(err)
+	}
+	moovDur := decCropped.Moov.Mvhd.Duration
+	moovTimescale := decCropped.Moov.Mvhd.Timescale
+	if uint64(cropDur)*uint64(moovTimescale) != moovDur*1000 {
+		t.Errorf("got %d/%dms instead of %dms", moovDur, moovTimescale, cropDur)
+	}
+}