From f0368342a7e59ff86b221e364110bc43f0f426b7 Mon Sep 17 00:00:00 2001
From: Greg Baker <ggbaker@sfu.ca>
Date: Fri, 20 May 2022 11:40:27 -0700
Subject: [PATCH] command to extract specific GPMF values to an ndjson file

---
 bin/gopro-data-extract.py | 107 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 107 insertions(+)
 create mode 100644 bin/gopro-data-extract.py

diff --git a/bin/gopro-data-extract.py b/bin/gopro-data-extract.py
new file mode 100644
index 00000000..9ad1e824
--- /dev/null
+++ b/bin/gopro-data-extract.py
@@ -0,0 +1,107 @@
+import argparse
+import json
+
+from gopro_overlay.ffmpeg import load_gpmd_from
+from gopro_overlay.gpmd import GoproMeta, interpret_item
+
+
+class DataDumpVisitor:
+    def __init__(self, fourcc, converter):
+        self._fourcc = fourcc
+        self._converter = converter
+        self._counter = 0
+
+    def vic_DEVC(self, item, contents):
+        return self
+
+    def vic_STRM(self, item, contents):
+        return DataDumpStreamVisitor(
+            fourcc = self._fourcc,
+            visit=lambda fourcc, c: self._converter(self._counter, fourcc, c)
+        )
+
+    def v_end(self):
+        self._counter += 1
+        pass
+
+
+class DataDumpStreamVisitor:
+    def __init__(self, fourcc, visit):
+        self._fourcc = fourcc
+        self._visit = visit
+        self._scale = None
+
+    def vi_SCAL(self, item):
+        self._scale = interpret_item(item)
+
+    def __getattr__(self, attr):
+        if attr in ['vi_' + self._fourcc, 'vi_GPSU']:
+            def vi(item):
+                data = interpret_item(item, self._scale)
+                self._visit(item.fourcc, data)
+                return data
+            return vi
+        else:
+            raise AttributeError(attr)
+
+    def v_end(self):
+        pass
+
+
+class DumpAggregateConverter:
+    def __init__(self, file):
+        self.time = None
+        self.file = file
+        self.queue = []
+
+    def output(self, start, end, queue):
+        if not queue:
+            return
+
+        # assume uniform distribution of values between two timestamps
+        delta = (end - start) / len(queue)
+        for i, item in enumerate(queue):
+            t = start + delta*i
+            d = {'timestamp': t.isoformat()}
+
+            if hasattr(item, '_asdict'):
+                d |= item._asdict()
+            else:
+                d['value'] = item
+
+            json.dump(d, self.file)
+            self.file.write('\n')
+
+    def convert(self, counter, fourcc, data):
+        # Find values we are interested in, bracketed between GPSU time stamps.
+        if fourcc == 'GPSU':
+            if self.time:
+                start = self.time
+                end = data
+                self.output(start, end, self.queue)
+            self.time = data
+            self.queue = []
+        else:
+            if isinstance(data, list):
+                self.queue.extend(data)
+            else:
+                self.queue.append(data)
+
+
+def dump(input_file, fourcc, output_file):
+    gpmd_from = load_gpmd_from(input_file)
+    meta = GoproMeta.parse(gpmd_from)
+
+    with open(output_file, 'wt', encoding='utf-8') as file:
+        converter = DumpAggregateConverter(file)
+        meta.accept(DataDumpVisitor(fourcc=fourcc, converter=converter.convert))
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser(description="Extract GoPro metadata")
+    parser.add_argument("input", help="Input file")
+    parser.add_argument("output", help="Output NDJSON file")
+    parser.add_argument("--fourcc", "-f", action="store", default='ACCL', help='GPMD fourcc field to extract')
+
+    args = parser.parse_args()
+    dump(args.input, args.fourcc, args.output)