[TASK] Implement backend logic to process uploaded videos and add subtitles

[Mario-SO]

Description

Develop backend logic to handle video processing and subtitle addition using FFMPEG.

Related User Story

#633

Objectives

• [ ] Set up FFMPEG integration for subtitle embedding using Livepeer API response
• [ ] Implement temporary storage and cleanup for downloaded videos

Acceptance Criteria

• [ ] Videos are successfully downloaded after Livepeer processing
• [ ] FFMPEG correctly embeds subtitles into video metadata
• [ ] New API endpoints for subtitle operations are functional
• [ ] Downloaded videos are stored in a temp/ folder and deleted after processing

Additional Information

Ensure proper error handling and logging throughout the process. Consider implementing a job queue for processing multiple videos efficiently.