Apple AVKit AVAsset tracks method does not see all tracks in GoPro .mp4 files

Question

I'm trying to read the GPS data from a GoPro camera, and the "tracks" method on AVAsset only lists three tracks, while there are actually five, according to ffmpeg.

What can I do to see all the tracks? I'm particularly interested in the GPMF track that contains GPS data.

Here's what AVAsset produces:

    NSArray *trackA = asset.tracks;
    index = 0;
    for (AVAssetTrack *track in trackA) {
        XLog(@"%ld. trackID = %d", index, track.trackID);
        XLog(@"%ld. mediaType = %@", index, track.mediaType);
        XLog(@"%ld. data size = %@", index, NSStringFromSize(track.naturalSize));
        XLog(@"___________________________");
      index++;
    }

AVAsset creation date = 2022-11-13 13:33:57 +0000
AVAsset metadata = 2022-11-13 13:33:57 +0000
0. trackID = 1
0. mediaType = vide
0. data size = {3840, 2160}
___________________________
1. trackID = 2
1. mediaType = soun
1. data size = {0, 0}
___________________________
2. trackID = 3
2. mediaType = tmcd
2. data size = {0, 0}

while here is what ffmpeg produces.

ffmpeg -i GX010045.MP4

ffmpeg version 5.1.2 Copyright (c) 2000-2022 the FFmpeg developers
  built with Apple clang version 14.0.0 (clang-1400.0.29.202)

...

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'GX010045.MP4':
  Metadata:
    major_brand     : mp41
    minor_version   : 538120216
    compatible_brands: mp41
    creation_time   : 2022-11-13T13:33:57.000000Z
    location        : +38.0357-122.5819/
    location-eng    : +38.0357-122.5819/
    firmware        : HD9.01.01.72.00
  Duration: 00:08:52.54, start: 0.000000, bitrate: 60206 kb/s
  Stream #0:0[0x1](eng): Video: hevc (Main) (hvc1 / 0x31637668), yuvj420p(pc, bt709), 3840x2160 [SAR 1:1 DAR 16:9], 59941 kb/s, 59.94 fps, 59.94 tbr, 60k tbn (default)
    Metadata:
      creation_time   : 2022-11-13T13:33:57.000000Z
      handler_name    : GoPro H.265
      vendor_id       : [0][0][0][0]
      encoder         : GoPro H.265 encoder
      timecode        : 13:33:09:07
  Stream #0:1[0x2](eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 189 kb/s (default)
    Metadata:
      creation_time   : 2022-11-13T13:33:57.000000Z
      handler_name    : GoPro AAC  
      vendor_id       : [0][0][0][0]
      timecode        : 13:33:09:07
  Stream #0:2[0x3](eng): Data: none (tmcd / 0x64636D74) (default)
    Metadata:
      creation_time   : 2022-11-13T13:33:57.000000Z
      handler_name    : GoPro TCD  
      timecode        : 13:33:09:07
  Stream #0:3[0x4](eng): Data: bin_data (gpmd / 0x646D7067), 48 kb/s (default)
    Metadata:
      creation_time   : 2022-11-13T13:33:57.000000Z
      handler_name    : GoPro MET  
  Stream #0:4[0x5](eng): Data: none (fdsc / 0x63736466), 13 kb/s (default)
    Metadata:
      creation_time   : 2022-11-13T13:33:57.000000Z
      handler_name    : GoPro SOS  
At least one output file must be specified

Answer 1

AVAsset simply reports tracks that Apple is interested in. You have to write an .mp4 parser to find the tracks that other providers add (like GoPro).