WebRTC stream recording to S3

I would suggest two options:

1. Stream into Kinesis Video Stream.
   KVS uses Amazon S3 as the underlying data store, which means you can set and control retention periods on a per-stream basis for a limited time period or indefinitely. You can change the stream retention period at any point. You can retrieve the video using the GetMedia API: https://docs.aws.amazon.com/kinesisvideostreams/latest/dg/API_dataplane_GetMedia.html https://github.com/aws/amazon-kinesis-video-streams-parser-library#kinesisvideoexample

2. Automate the S3 part wtih AWS Elemental MediaConvert
   You can setup an assembly workflow job and stitch together multiple inputs file https://docs.aws.amazon.com/mediaconvert/latest/ug/assembling-multiple-inputs-and-input-clips.html

However, there are other options (e.g. AWS Marketplace or KVS consumers) but I would explore the above first.