Set output file mtime to match embedded capture time

Some tools (Synology Photos, for videos) key off filesystem mtime
rather than parsing QuickTime metadata for the capture date, so an
otherwise-correct output file would sort/date wrong there. Stamp the
output's mtime from the same clip whose metadata got embedded
(--metadata-from) after encoding.

README.md

@@ -31,6 +31,9 @@ This script:
    with a plain stream copy) and concatenates everything into one file.
 5. Carries over the original container metadata (GPS, device info, creation
    time, Live Photo identifiers) from one of the source clips.
+6. Sets the output file's filesystem modification time to match that same
+   capture time — some tools (e.g. Synology Photos, for videos) sort/date
+   by file mtime instead of parsing embedded metadata.
 
 Audio stays uncompressed PCM throughout, so it never loses quality. Video
 quality defaults to a bitrate slightly above the source clips' own bitrate

concat_live_clips.py

@@ -28,6 +28,7 @@ Requirements:
       detects clip overlap): pip install --user numpy
 """
 import argparse
+import os
 import re
 import subprocess
 import sys
@@ -365,6 +366,17 @@ def main():
 
     print(f"Encoding seamless, deduplicated output -> {output}", file=sys.stderr)
     subprocess.run(cmd, check=True)
+
+    creation_dt = fetch_creation_time(clips[args.metadata_from])
+    if creation_dt is not None:
+        ts = creation_dt.timestamp()
+        os.utime(output, (ts, ts))
+        print(f"Set file mtime to {creation_dt.isoformat()} (matches embedded metadata, "
+              f"so apps that key off filesystem time instead of parsing video metadata "
+              f"still sort/date it correctly)", file=sys.stderr)
+    else:
+        print("warning: couldn't determine source creation time; leaving file mtime as-is", file=sys.stderr)
+
     print(f"Done: {output}", file=sys.stderr)