Initial standalone Recorder+Converter implementation

[sgfn]

Changes from ex_webrtc v0.8.1

Features

• Converter now combines video and audio tracks belonging to the same stream, syncs them and outputs a WEBM file
  • When using simulcast, this results in 3 output files, one per layer
• Converter can generate thumbnails for the result files
• Recorder can upload the RTP dumps to S3-compatible storage
• Converter can download the RTP dumps from S3-compatible storage, and upload the conversion results there as well

Breaking changes

Recorder

• Recorder now has a controlling process to which it sends messages
  • At the moment, messages are sent only when using S3 uploads
• The nomenclature of report (and the report.json file) was changed to manifest (manifest.json)
• add_tracks/2 now returns {:ok, manifest :: Recorder.manifest()}
  • manifest contains only the parts relevant to the added tracks, and not the entire manifest of the Recorder

Converter

• Converter now generates WEBM files using FFmpeg, so it requires the ffmpeg binary with the relevant libraries present in PATH
• convert!/2 now accepts t:Converter.options/0 as the second argument

Non-breaking important changes

Recorder

• New function end_tracks/2 that closes the relevant file handles and optionally schedules the S3 upload

Converter

• convert!/2 can also accept t:Recorder.manifest/0 as the first argument (e.g. the manifest returned by Recorder.end_tracks/2)