adds documentation (#250)

* adds documentation

* updates in user docs

* documentation

Co-authored-by: styiannis <1515939+styiannis@users.noreply.github.com>

docs/developers_docs.md

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+# Developers documentation
+
+## Table of contents
+- [System architecture](#system-architecture)
+- [API documentation](#api-documentation)
+- [Working with Docker tips](#working-with-docker-tips)
+- [How video is transcoded](#how-video-is-transcoded)
+
+
+## System architecture
+
+## API documentation
+API is documented using Swagger - checkout ot http://your_installation/swagger
+This page allows you to login to perform authenticated actions - it will also use your session if logged in. 
+
+
+## Working with Docker tips
+
+To perform the Docker installation, follow instructions to install Docker + Docker compose (docs/Docker_Compose.md) and then build/start docker-compose-dev.yaml . This will run the frontend application on port 8088 on top of all other containers (including the Django web application on port 80)
+
+```
+docker-compose -f docker-compose-dev.yaml build
+docker-compose -f docker-compose-dev.yaml up
+```
+
+### Frontend application changes
+Eg change `frontend/src/static/js/pages/HomePage.tsx` , dev application refreshes in a number of seconds (hot reloading) and I see the changes, once I'm happy I can run
+
+```
+docker-compose -f docker-compose-dev.yaml -T frontend npm run dist
+```
+
+And then in order for the changes to be visible on the application while served through nginx, 
+
+```
+cp -r frontend/dist/static/* static/
+```
+
+POST calls: cannot be performed through the dev server, you have to make through the normal application (port 80) and then see changes on the dev application on port 8088. 
+Make sure the urls are set on `frontend/.env` if different than localhost
+
+
+Media page: need to upload content through the main application (nginx/port 80), and then use an id for page media.html, for example `http://localhost:8088/media.html?m=nc9rotyWP`
+
+There are some issues with CORS too to resolve, in order for some pages to function, eg the manage comments page
+
+```http://localhost:8088/manage-media.html px manage_media
+```
+
+### Backend application changes
+After I make changes to the django application (eg make a change on `files/forms.py`) in order to see the changes I have to restart the web container
+
+```
+docker-compose -f docker-compose-dev.yaml restart web
+```
+
+## How video is transcoded
+
+Original files get uploaded to the application server, and they get stored there as FileFields.
+
+If files are videos and the duration is greater than a number (defined on settings, I think 4minutes), they are also broken in chunks, so one Encode object per chunk, for all enabled EncodeProfiles.
+
+Then the workers start picking Encode objects and they transcode the chunks, so if a chunk gets transcoded correctly, the original file (the small chunk) gets replaced by the transcoded file, and the Encode object status is marked as 'success'.
+
+
+original.mp4 (1G, 720px)--> Encode1 (100MB, 240px, chunk=True), Encode2 (100MB, 240px, chunk=True)...EncodeXX (100MB, 720px, chunk=True) ---> when all Encode objects are success, for a resolution, they get concatenated to the original_resolution.mp4 file and this gets stored as Encode object (chunk=False). This is what is available for download.
+
+Apparently the Encode object is used to store Encoded files that are served eventually (chunk=False, status='success'), but also files while they are on their way to get transcoded (chunk=True, status='pending/etc')
+
+(Parenthesis opening)
+there is also an experimental small service (not commited to the repo currently) that speaks only through API and a) gets tasks to run, b) returns results. So it makes a request and receives an ffmpeg command, plus a file, it runs the ffmpeg command, and returns the result.I've used this mechanism on a number of installations to migrate existing videos through more servers/cpu and has worked with only one problem, some temporary files needed to be removed from the servers (through a periodic task, not so big problem)
+(Parenthesis closing)
+
+
+When the Encode object is marked as success and chunk=False, and thus is available for download/stream, there is a task that gets started and saves an HLS version of the file (1 mp4-->x number of small .ts chunks). This would be FILES_C
+
+This mechanism allows for workers that have access on the same filesystem (either localhost, or through a shared network filesystem, eg NFS/EFS) to work on the same time and produce results.