GoPro Metadata Format Parser

TLDR:

1. ffmpeg -y -i GOPR0001.MP4 -codec copy -map 0:m:handler_name:" GoPro MET" -f rawvideo GOPR0001.bin
2. gopro2json -i GOPR0001.bin -o GOPR0001.json
3. There is no step 3

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I spent some time trying to reverse-engineer the GoPro Metadata Format (GPMD or GPMDF) that is stored in GoPro Hero 5 cameras if GPS is enabled. This is what I found.

Part of this code is in production on Earthscape; for an example of what you can do with the extracted data, see this video.

If you enjoy working on this sort of thing, please see our careers page.

Extracting the Metadata File

The metadata stream is stored in the .mp4 video file itself alongside the video and audio streams. We can use ffprobe to find it:

[computar][100GOPRO] ➔ ffprobe GOPR0008.MP4
ffprobe version 3.2.4 Copyright (c) 2007-2017 the FFmpeg developers
[SNIP]
    Stream #0:3(eng): Data: none (gpmd / 0x646D7067), 33 kb/s (default)
    Metadata:
      creation_time   : 2016-11-22T23:42:41.000000Z
      handler_name    : 	GoPro MET
[SNIP]

We can identify it by the gpmd in the tag string - in this case it's id 3. We can then use ffmpeg to extract the metadata stream into a binary file for processing:

ffmpeg -y -i GOPR0001.MP4 -codec copy -map 0:3 -f rawvideo out-0001.bin

This leaves us with a binary file with the data.

Data We Get

• ~400 Hz 3-axis gyro readings
• ~200 Hz 3-axis accelerometer readings
• ~18 Hz GPS position (lat/lon/alt/spd)
• 1 Hz GPS timestamps
• 1 Hz GPS accuracy (cm) and fix (2d/3d)
• 1 Hz temperature of camera

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The Protocol

Data starts with a label that describes the data following it. Values are all big endian, and floats are IEEE 754. Everything is packed to 4 bytes where applicable, padded with zeroes so it's 32-bit aligned.

• Labels - human readable types of proceeding data
• Type - single ascii character describing data
• Size - how big is the data type
• Count - how many values are we going to get
• Length = size * count

Labels include:

• ACCL - accelerometer reading x/y/z
• DEVC - device
• DVID - device ID, possibly hard-coded to 0x1
• DVNM - devicde name, string "Camera"
• EMPT - empty packet
• GPS5 - GPS data (lat, lon, alt, speed, 3d speed)
• GPSF - GPS fix (none, 2d, 3d)
• GPSP - GPS positional accuracy in cm
• GPSU - GPS acquired timestamp; potentially different than "camera time"
• GYRO - gryroscope reading x/y/z
• SCAL - scale factor, a multiplier for subsequent data
• SIUN - SI units; strings (m/s², rad/s)
• STRM - ¯\_(ツ)_/¯
• TMPC - temperature
• TSMP - total number of samples
• UNIT - alternative units; strings (deg, m, m/s)

Types include:

• c - single char
• L - unsigned long
• s - signed short
• S - unsigned short
• f - 32 float

For implementation details, see reader.go and other corresponding files in telemetry/.