Encode captions lambda

[cjjenkinson]

The final part of the video transcribing workflow is encoding the audio transcription back onto the video.

These comprises of a number of steps:

1. Store the SRT transcription file (the transcribed words from the audio from Assembly a.i) from the audio bucket into the tmp writable space within the lambda
2. Store the original video in the tmp write store
3. Prepare the arguments required for ffmpeg to burn the SRT subtitles onto the original video

ffmpeg -i input.mp4 -map 0 -c copy -c:s mov_text -metadata:s:s:0 language=eng -metadata:s:s:1 language=ipk output.mp4

Reference: https://askubuntu.com/questions/214199/how-do-i-add-and-or-keep-subtitles-when-converting-video

Notes: we want to ensure the input and output name are clear as the input video is the referencing the original video with the audio included and the output video will be the video that will have the captions encoded onto it.

4. Store the encoded output video into the output-video bucket and update the video job from Dynamo as complete
5. Sanity check the process worked by viewing the output video and then tweaking the subtitle styling to suit your preferences

See: https://stackoverflow.com/questions/21363334/how-to-add-font-size-in-subtitles-in-ffmpeg-video-filter