Added back a main README.

Author: fnunnari

README.md

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+RecSyncNG is a video recording app with sub-millisecond synchronization accuracy for multiple Android smartphones,
+useful for creating affordable and easy-to-setup multi-view camera systems for robotics, SLAM, 3D-reconstruction, panorama stitching.
+
+RecSynchNG is a fork of the original [RecSynch-android](https://github.com/MobileRoboticsSkoltech/RecSync-android) project. Here is the [original README](README-orig.md).
+
+The original project has been improved with a remote GUI allowing for remote control of the android devices, centralized video download capability,
+ and a revised post-processing stage for the deployment of perfectly synchronized videos.
+
+
+## Installation and setup
+
+(Use img from the slides)
+
+
+### Requirements
+
+* A set of Android devices, _all of the same hardware type_, with Android version 10+. (We were able to compile and run on Android 8, but not tested since a while)
+* Elect a _Leader_ android device:
+  * must have an adaptor for Ethernet connection;
+  * must be able to configure the ethernet with static IP address;
+  * must be able to configure Hotspot (share Ethernet via WiFi):
+    * not all devices can by default enable Hotspot without a SIM card. To circumvent some limited GUIs, we are using the `VPNHotspot` app.
+* A laptop/PC with Python 3.9 and an ethernet adaptor
+
+### Android devices installation and setup
+
+* Install the RecSynchNG apk on all devices
+* Select one device as _Leader_:
+  * configure its Ethernet adaptor with:
+    * Static IP: 192.168.5.2
+    * Mask: 255.255.255.0
+    * Gateway 192.168.5.1
+  * Start a Wi-Fi hotspot, sharing the Ethernet connection.
+* Connect all other android devices to the Hotspot WiFi network.
+
+
+The master app should display now the connected clients and buttons for recording control
+
+### Remote controlling PC installation and setup
+
+Configure the ethernet adaptor of your PC as: 
+* Static IP: 192.168.5.1
+* Mask: 255.255.255.0
+* Gateway 192.168.5.1
+
+Cable connect the PC and the Master device.
+
+Verify the Ethernet connection with Ping. E.g., from the PC, in a terminal
+
+```
+ping 192.168.5.2
+
+64 bytes from 192.168.5.2: icmp_seq=347 ttl=125 time=2.425 ms
+64 bytes from 192.168.5.2: icmp_seq=348 ttl=125 time=2.233 ms
+64 bytes from 192.168.5.2: icmp_seq=349 ttl=125 time=7.560 ms
+64 bytes from 192.168.5.2: icmp_seq=350 ttl=125 time=2.288 ms
+```
+
+
+Setup a python environment using Python 3.9+.
+
+```
+cd PythonTools
+python3 -m venv p3env-RecSynchNG
+source p3env-RecSynchNG/bin/activate
+pip install -r requirements.txt
+```
+
+For the post-processing of the videos, you need to install ffmpeg executable. E.g.:
+* On Linux: `apt install ffmpeg`
+* On Mac: `brew install ffmpeg`
+
+
+## Usage
+
+### Run the software
+
+(Android) First, start the app on all Android devices:
+* Wait a few seconds for synchronization;
+* on client devices you should see the client ID and info about the connection status; 
+* on the leader device you should see the list of connected clients.
+
+Second, start the software on the controlling PC.
+
+On one terminal **start the http file server**. It starts a small http server ready to receive the recorded files from the android devices:
+
+```
+cd PythonTools
+source p3env-RecSynchNG/bin/activate
+python FileServer.py
+```
+
+TODO -- pic of the server console
+
+On another terminal, **start the remote controlling GUI** :
+
+```
+cd PythonTools
+source p3env-RecSynchNG/bin/activate
+python RemoteController.py
+```
+
+TODO -- pic of the GUI
+
+
+### Recording video
+
+1.  [Optional step] Press the ```calculate period``` button. The app will analyze frame stream and use the calculated frame period in further synchronization steps.
+2.  Adjust exposure and ISO to your needs.
+3.  Press the ```phase align``` button.
+4.  Press the ```record video``` button to start synchronized video recording.
+5.  Get videos from RecSync folder in smartphone root directory.
+
+### Extraction and matching of the frames
+
+
+
+## Citations / Credits
+
+If you use this application, please cite [Sub-millisecond Video Synchronization of Multiple Android Smartphones](https://arxiv.org/abs/2107.00987):
+```
+@misc{akhmetyanov2021submillisecond,
+      title={Sub-millisecond Video Synchronization of Multiple Android Smartphones}, 
+      author={Azat Akhmetyanov and Anastasiia Kornilova and Marsel Faizullin and David Pozo and Gonzalo Ferrer},
+      year={2021},
+      eprint={2107.00987},
+      archivePrefix={arXiv},
+      primaryClass={cs.CV}
+}
+```
+
+This work is based on "Wireless Software Synchronization of Multiple Distributed Cameras"
+
+Reference code for the paper
+[Wireless Software Synchronization of Multiple Distributed Cameras](https://arxiv.org/abs/1812.09366).
+_Sameer Ansari, Neal Wadhwa, Rahul Garg, Jiawen Chen_, ICCP 2019.