Chapter titles missing when writing with AVAssetWriter

Question

Created Feb ’24

Replies 2

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Participants 2

I'm writing a video that's recorded in realtime while the app is running. The user has the option to insert bookmarks during this time.

I'm trying to write these bookmarks as chapters into the recorded video file, but I'm having some trouble.

ffplay displays the chapters with the right start and end times, but not the title. Also neither QuickTime Player nor AVAsset see the chapters.

This is how I set it up (assetWriter and videoInput not shown):

      let metadataItem = AVMutableMetadataItem()
      metadataItem.identifier = AVMetadataIdentifier.commonIdentifierTitle
      metadataItem.value = "title" as (NSCopying & NSObjectProtocol)
      metadataItem.dataType = kCMMetadataBaseDataType_UTF8 as String
      metadataItem.extendedLanguageTag = "en"

      let dummyGroup = AVTimedMetadataGroup(items: [metadataItem], timeRange: CMTimeRange(start: CMTime.zero, end: CMTime.invalid))

      let metaFmt = dummyGroup.copyFormatDescription()

      textWriterInput = AVAssetWriterInput(mediaType: .metadata, outputSettings: nil, sourceFormatHint: metaFmt)
      textWriterInput.languageCode = "en"
      textWriterAdaptor = AVAssetWriterInputMetadataAdaptor(assetWriterInput: textWriterInput)

      assetWriter.add(textWriterInput)
      videoInput.addTrackAssociation(withTrackOf: textWriterInput, type: AVAssetTrack.AssociationType.chapterList.rawValue)

and this happens when a bookmark is inserted (parameters time and title):

    let metadataItem = AVMutableMetadataItem()
    metadataItem.identifier = AVMetadataIdentifier.commonIdentifierTitle
    metadataItem.value = title as (NSCopying & NSObjectProtocol)
    metadataItem.dataType = kCMMetadataBaseDataType_UTF8 as String
    metadataItem.extendedLanguageTag = "en"

    let group = AVTimedMetadataGroup(items: [metadataItem], timeRange: CMTimeRange(start: time, duration: CMTime.invalid))

    if textWriterInput.isReadyForMoreMediaData {
        self.textWriterAdaptor.append(group)
    }

This is what ffplay has to say about the recording:

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/path/to/video.mp4':
  Metadata:
    major_brand     : mp42
    minor_version   : 1
    compatible_brands: isommp41mp42
    creation_time   : 2024-02-01T16:37:28.000000Z
  Duration: 00:00:14.48, start: 0.142993, bitrate: 13226 kb/s
  Chapters:
    Chapter #0:0: start 6.727000, end 12.020000
      Metadata:
        title           : 
    Chapter #0:1: start 12.020000, end 14.622000
      Metadata:
        title           : 
  Stream #0:0[0x1](und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(progressive), 2060x1080, 13268 kb/s, 57.81 fps, 300 tbr, 600 tbn (default)
    Metadata:
      creation_time   : 2024-02-01T16:37:28.000000Z
      handler_name    : Core Media Video
      vendor_id       : [0][0][0][0]
  Stream #0:1[0x3](und): Audio: aac (HE-AAC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 57 kb/s (default)
    Metadata:
      creation_time   : 2024-02-01T16:37:28.000000Z
      handler_name    : Core Media Audio
      vendor_id       : [0][0][0][0]
  Stream #0:2[0x4](eng): Data: bin_data (mebx / 0x7862656D), 0 kb/s (default)
    Metadata:
      creation_time   : 2024-02-01T16:37:28.000000Z
      handler_name    : Core Media Metadata
   2.05 A-V: -0.001 fd=  24 aq=   35KB vq= 6576KB sq=    0B f=0/0

Anyone got an idea why the titles/chapters won't show up?

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Answer 1

JWWalker OP

Feb ’24

Years ago I wrote code that created a movie with chapter titles that showed up in QuickTime Player. At some point it stopped working, possibly due to changes in QuickTime Player. I don't know whether today's QuickTime Player is even capable of showing chapter titles. But for what it's worth, I can tell you that my text track used a media type of text, not metadata.

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Answer 2

harrald OP

Feb ’24

Yes chapters do work in QuickTime Player, it happily shows ones created with ffmpeg. Those are in fact in a text track, not mebx.

I've seen references to text tracks on the net, however I've had no luck creating one and getting a working movie file out. There doesn't seem to be an adapter (besides AVAssetWriterInputCaptionAdaptor, which also didn't work) to write to the text track.

Any chance you could show some code?

0