Fetch start timecode from metadata

Audio files can be created using a start timecode. This should be extracted from the audio file and the audio player and results start times offset accordinly.

49778972_358083545027598_7495642805482553344_n

Using the command

ffprobe -print_format json -show_streams -show_format JULEMKAMB0052_med_TC.wav

yields

ffprobe version 4.1 Copyright (c) 2007-2018 the FFmpeg developers
  built with Apple LLVM version 10.0.0 (clang-1000.11.45.5)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/4.1_1 --enable-shared --enable-pthreads --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gpl --enable-libmp3lame --enable-libopus --enable-libsnappy --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-lzma --enable-opencl --enable-videotoolbox
  libavutil      56. 22.100 / 56. 22.100
  libavcodec     58. 35.100 / 58. 35.100
  libavformat    58. 20.100 / 58. 20.100
  libavdevice    58.  5.100 / 58.  5.100
  libavfilter     7. 40.101 /  7. 40.101
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  3.100 /  5.  3.100
  libswresample   3.  3.100 /  3.  3.100
  libpostproc    55.  3.100 / 55.  3.100
{
Input #0, wav, from 'JULEMKAMB0052_med_TC.wav':
  Metadata:
    encoded_by      : Adobe Premiere Pro CC 2018.1 (Wi
    date            : 2019-01-07
    creation_time   : 09:08:04
    time_reference  : 1792416000
  Duration: 00:00:22.12, bitrate: 1540 kb/s
    Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, 2 channels, s16, 1536 kb/s
    "streams": [
        {
            "index": 0,
            "codec_name": "pcm_s16le",
            "codec_long_name": "PCM signed 16-bit little-endian",
            "codec_type": "audio",
            "codec_time_base": "1/48000",
            "codec_tag_string": "[1][0][0][0]",
            "codec_tag": "0x0001",
            "sample_fmt": "s16",
            "sample_rate": "48000",
            "channels": 2,
            "bits_per_sample": 16,
            "r_frame_rate": "0/0",
            "avg_frame_rate": "0/0",
            "time_base": "1/48000",
            "duration_ts": 1061760,
            "duration": "22.120000",
            "bit_rate": "1536000",
            "disposition": {
                "default": 0,
                "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
            }
        }
    ],
    "format": {
        "filename": "JULEMKAMB0052_med_TC.wav",
        "nb_streams": 1,
        "nb_programs": 0,
        "format_name": "wav",
        "format_long_name": "WAV / WAVE (Waveform Audio)",
        "duration": "22.120000",
        "size": "4259344",
        "bit_rate": "1540449",
        "probe_score": 99,
        "tags": {
            "encoded_by": "Adobe Premiere Pro CC 2018.1 (Wi",
            "date": "2019-01-07",
            "creation_time": "09:08:04",
            "time_reference": "1792416000"
        }
    }
}

To calculate the start timecode, we need to divide the time_reference by sample_rate to get seconds since midnight: 1792416000/48000 = 10:22:22:00.

Check to see if https://github.com/CrystalComputerCorp/smpte-timecode can help with the conversion. Alternatively check if MediaInfo or ExifTool can be used.

Should be possible to use with https://github.com/fluent-ffmpeg/node-fluent-ffmpeg#reading-video-metadata

nrkno / transcriber-frontend

Fetch start timecode from metadata #44