GPS Time Sync Questions

[JStoschek]

Hello,

I have 3 GoPro Hero 10s. I am trying to get the exact time at which each frame from each GoPro was captured for computer vision tasks. I am looking at the GPS Time Synchronization feature and figured this might be helpful. I ran a test with one of my GoPros and got the below metadata when probing via ffmpeg.

My question is what does the time in the timecode refer to? Is it current GPS time? or time since power on? Secondly, is there a better way to get all of the metadata from the MP4 other than ffmpeg prope?
Any help would be greatly appreciated.

Metadata Snippet:
'tags': {'creation_time': '2024-07-16T14:47:05.000000Z',
'language': 'eng',
'handler_name': '\x0bGoPro H.265',
'vendor_id': '[0][0][0][0]',
'encoder': 'GoPro H.265 encoder',
'timecode': '04:15:32:29'}}

Full Metadata:
{'streams': [{'index': 0,
'codec_name': 'hevc',
'codec_long_name': 'H.265 / HEVC (High Efficiency Video Coding)',
'profile': 'Main',
'codec_type': 'video',
'codec_tag_string': 'hvc1',
'codec_tag': '0x31637668',
'width': 3840,
'height': 2160,
'coded_width': 3840,
'coded_height': 2160,
'closed_captions': 0,
'has_b_frames': 0,
'sample_aspect_ratio': '1:1',
'display_aspect_ratio': '16:9',
'pix_fmt': 'yuvj420p',
'level': 153,
'color_range': 'pc',
'color_space': 'bt709',
'color_transfer': 'bt709',
'color_primaries': 'bt709',
'chroma_location': 'left',
'refs': 1,
'r_frame_rate': '30000/1001',
'avg_frame_rate': '30000/1001',
'time_base': '1/30000',
'start_pts': 0,
'start_time': '0.000000',
'duration_ts': 354354,
'duration': '11.811800',
'bit_rate': '46831739',
'nb_frames': '354',
'disposition': {'default': 1,
'dub': 0,
'original': 0,
'comment': 0,
'lyrics': 0,
'karaoke': 0,
'forced': 0,
'hearing_impaired': 0,
'visual_impaired': 0,
'clean_effects': 0,
'attached_pic': 0,
'timed_thumbnails': 0},
'tags': {'creation_time': '2024-07-16T14:47:05.000000Z',
'language': 'eng',
'handler_name': '\x0bGoPro H.265',
'vendor_id': '[0][0][0][0]',
'encoder': 'GoPro H.265 encoder',
'timecode': '04:15:32:29'}},
{'index': 1,
'codec_name': 'aac',
'codec_long_name': 'AAC (Advanced Audio Coding)',
'profile': 'LC',
'codec_type': 'audio',
'codec_tag_string': 'mp4a',
'codec_tag': '0x6134706d',
'sample_fmt': 'fltp',
'sample_rate': '48000',
'channels': 2,
'channel_layout': 'stereo',
'bits_per_sample': 0,
'r_frame_rate': '0/0',
'avg_frame_rate': '0/0',
'time_base': '1/48000',
'start_pts': 0,
'start_time': '0.000000',
'duration_ts': 566272,
'duration': '11.797333',
'bit_rate': '189591',
'nb_frames': '553',
'disposition': {'default': 1,
'dub': 0,
'original': 0,
'comment': 0,
'lyrics': 0,
'karaoke': 0,
'forced': 0,
'hearing_impaired': 0,
'visual_impaired': 0,
'clean_effects': 0,
'attached_pic': 0,
'timed_thumbnails': 0},
'tags': {'creation_time': '2024-07-16T14:47:05.000000Z',
'language': 'eng',
'handler_name': '\x0bGoPro AAC ',
'vendor_id': '[0][0][0][0]',
'timecode': '04:15:32:29'}},
{'index': 2,
'codec_type': 'data',
'codec_tag_string': 'tmcd',
'codec_tag': '0x64636d74',
'r_frame_rate': '0/0',
'avg_frame_rate': '30000/1001',
'time_base': '1/30000',
'start_pts': 0,
'start_time': '0.000000',
'duration_ts': 354354,
'duration': '11.811800',
'bit_rate': '2',
'nb_frames': '1',
'disposition': {'default': 1,
'dub': 0,
'original': 0,
'comment': 0,
'lyrics': 0,
'karaoke': 0,
'forced': 0,
'hearing_impaired': 0,
'visual_impaired': 0,
'clean_effects': 0,
'attached_pic': 0,
'timed_thumbnails': 0},
'tags': {'creation_time': '2024-07-16T14:47:05.000000Z',
'language': 'eng',
'handler_name': '\x0bGoPro TCD ',
'timecode': '04:15:32:29'}},
{'index': 3,
'codec_name': 'bin_data',
'codec_long_name': 'binary data',
'codec_type': 'data',
'codec_tag_string': 'gpmd',
'codec_tag': '0x646d7067',
'r_frame_rate': '0/0',
'avg_frame_rate': '0/0',
'time_base': '1/1000',
'start_pts': 0,
'start_time': '0.000000',
'duration_ts': 11812,
'duration': '11.812000',
'bit_rate': '53222',
'nb_frames': '12',
'disposition': {'default': 1,
'dub': 0,
'original': 0,
'comment': 0,
'lyrics': 0,
'karaoke': 0,
'forced': 0,
'hearing_impaired': 0,
'visual_impaired': 0,
'clean_effects': 0,
'attached_pic': 0,
'timed_thumbnails': 0},
'tags': {'creation_time': '2024-07-16T14:47:05.000000Z',
'language': 'eng',
'handler_name': '\x0bGoPro MET '}}],
'format': {'filename': 'GX010093.MP4',
'nb_streams': 4,
'nb_programs': 0,
'format_name': 'mov,mp4,m4a,3gp,3g2,mj2',
'format_long_name': 'QuickTime / MOV',
'start_time': '0.000000',
'duration': '11.811800',
'size': '69555764',
'bit_rate': '47109340',
'probe_score': 100,
'tags': {'major_brand': 'mp41',
'minor_version': '538120216',
'compatible_brands': 'mp41',
'creation_time': '2024-07-16T14:47:05.000000Z',
'location': '+37.4***-122.0***/',
'location-eng': '+37.4***-122.0***/',
'firmware': 'H21.01.01.62.70'}}}

[dnewman-gpsw]

ffmpeg only get stock metadata, nothing custom, nothing frame based. Use https://gopro.github.io/labs/control/metadata/ for more GoPro header metadata. But all the metadata you will need to code and extract the GPS5 track, GPS9 is HERO11 (better than HERO10, more designed for your needs.) Code access for all GPMF data: https://gopro.github.io/gpmf-parser/

[JStoschek]

Thank you, I think the Code access for all GPMF data will have what I want.

[xiemeilong]

How can I read the timecode track? How many timecode in the track, one timecode per frame or only one start/end timecode

[dnewman-gpsw]

Timecode track is in QuickTime format. So dig into the Apple docs on MOV tracks and timecode.
Or just use tools like FFMPEG that reads standard timecode. It only stores the timecode for the first frame, which the most common for digital media.