user guide: add script to record on all cams from braid

strand-braid-user/scripts/record-mp4-video-braid-all-cams.py

@@ -0,0 +1,56 @@
+#!/usr/bin/env python
+import argparse
+import json
+import time
+import sys
+from urllib.parse import urlparse
+import requests  # https://docs.python-requests.org/en/latest/user/install
+
+
+class BraidProxy:
+    def __init__(self, braid_url):
+        self.callback_url = urlparse(braid_url)._replace(path="callback").geturl()
+        # Setup initial session
+        self.session = requests.session()
+        r = self.session.get(braid_url)
+        if r.status_code != requests.codes.ok:
+            print(f"request URL: {braid_url}")
+            print("request failed. response:")
+            print(r.text)
+            raise RuntimeError("connection to braid failed.")
+
+    def send(self, cmd_dict):
+        body = json.dumps(cmd_dict)
+        r = self.session.post(
+            self.callback_url, data=body, headers={"Content-Type": "application/json"}
+        )
+        if r.status_code != requests.codes.ok:
+            print(
+                "error making request, status code {}".format(r.status_code),
+                file=sys.stderr,
+            )
+            sys.exit(1)
+
+
+def main():
+    parser = argparse.ArgumentParser()
+
+    parser.add_argument(
+        "--braid-url",
+        type=str,
+        default="http://127.0.0.1:33333/",
+        help="URL of Braid",
+    )
+    args = parser.parse_args()
+    braid = BraidProxy(braid_url=args.braid_url)
+
+    braid.send({"DoRecordMp4Files": True})
+    print("Recording for 5 seconds...")
+    time.sleep(5.0)
+
+    braid.send({"DoRecordMp4Files": False})
+    print("...finished.")
+
+
+if __name__ == "__main__":
+    main()

strand-braid-user/users-guide/src/scripting-with-python.md

@@ -5,11 +5,16 @@ can also be controlled from a Python script. The general technique is to use a
 Python library to connect to a running Strand Cam (or Braid) program exactly
 like a web browser does it.
 
-## Demo: changing tracking settings from a Python script
+## Demo: recording a video using Strand Camera from a Python script
 
 TODO: describe how to use and modify the [`record-mp4-video.py`
 demo](https://github.com/strawlab/strand-braid/blob/main/strand-braid-user/scripts/record-mp4-video.py).
 
+## Demo: recording multiple videos using Braid from a Python script
+
+TODO: describe how to use and modify the [`record-mp4-video-braid-all-cams.py`
+demo](strand-braid-user/scripts/record-mp4-video-braid-all-cams.py).
+
 ## Advanced: automating manual actions
 
 TODO: describe how to use the developer tools to watch the network requests from