Back Channel

Bridge livestreams to RTMP & HLS on macOS.

Website · GitHub Releases · Issues

Back Channel is a macOS app for turning livestream URLs into RTMP or HLS outputs that fit into production workflows. It is designed for producers, newsroom teams, and technical creators who need a dependable bridge between web livestreams and downstream ingest systems.

At a Glance

• Converts livestream URLs into RTMP or HLS output
• Supports both GUI and CLI workflows
• Bundles its own core native tooling for end-user installs
• Offers a managed Python source runtime for yt-dlp + Streamlink, plus managed support updates
• Built for Apple Silicon Macs running macOS 13 or later

Website

• GitHub Pages: chrisgherbert.github.io/backchannel
• Source: website/
• Workflow: pages.yml

The marketing/documentation site deploys automatically through GitHub Actions when changes under website/ are pushed to main.

Release Checklist

1. Ensure standalone deno exists for managed support payloads.
2. Optional: set a portable Python runtime URL/archive for the managed Python source runtime build, or let the script use its tested default.
3. Create/update private release config:

cp -n scripts/release.env.example scripts/release.env

4. Fill scripts/release.env required values (DEV_ID_APP, AC_PROFILE, DENO_BINARY).
5. Run full signed + notarized GitHub release:

./scripts/github_release.sh --version X.Y.Z --notes-file /absolute/path/to/release-notes.md

6. To publish newer managed support payloads without cutting a full app release:

./scripts/publish_managed_support.sh

7. Confirm the GitHub app release includes:

• app zip
• app zip checksum
• backchannel-managed-support.json
• managed Python source runtime archive + checksum
• managed deno archive + checksum

8. Confirm the dedicated managed-support release was updated with the same managed assets.
9. Distribute:

open dist

Prerequisites

• macOS 13+
• portable ffmpeg / ffprobe binaries available for packaging
• standalone deno binary available for managed support packaging
• optional portable Python runtime archive/URL for managed Python source runtime packaging

These are release-time/build-time requirements, not end-user runtime requirements. The shipped app bundles or manages its own dependencies.

Run

swift run

Build & Release Workflows

1. Local Development Build

Fast local build:

swift build

Run directly from source:

swift run

Build Self-Contained .app

This creates dist/Back Channel.app and bundles the stable native tools ffmpeg and ffprobe into:

Contents/Resources/bin/

It also bundles a CLI launcher and installer:

• Contents/Resources/bin/backchannel
• Contents/Resources/bin/install-cli.sh

./scripts/package_app.sh

App icon (optional):

• Drop assets/AppIcon.png (or assets/AppIcon.icns) before packaging.
• The script will automatically convert PNG to .icns.

You can override tool paths:

FFMPEG_BINARY=/path/to/ffmpeg FFPROBE_BINARY=/path/to/ffprobe APP_ICON_FILE=/path/to/icon.png ./scripts/package_app.sh

Install terminal command from the packaged app:

"/Users/herbert/web/youtube-live-converter/dist/Back Channel.app/Contents/Resources/bin/install-cli.sh"

This installs to ~/.local/bin/backchannel by default (no sudo). For a system-wide install, override target dir:

CLI_TARGET_DIR=/usr/local/bin "/Users/herbert/web/youtube-live-converter/dist/Back Channel.app/Contents/Resources/bin/install-cli.sh"

Then run:

backchannel --help

The managed Python source runtime (yt-dlp + Streamlink) and deno are both managed separately as app support components rather than being sealed inside the .app bundle.

2. Packaging For Local Testing

Use the packaging script directly:

./scripts/package_app.sh

It will:

1. Build release binary.
2. Create dist/Back Channel.app.
3. Bundle required native tools into Contents/Resources/bin.
4. Apply ad-hoc signing (for local execution).

3. Signed + Notarized Release

Use the current release pipeline scripts:

First-time setup:

cp scripts/release.env.example scripts/release.env

Fill required values in scripts/release.env:

• DEV_ID_APP
• AC_PROFILE
• DENO_BINARY (standalone Mach-O binary for managed support payloads)

Optional managed-runtime settings:

• PYTHON_STANDALONE_URL or PYTHON_STANDALONE_ARCHIVE
• YTDLP_PACKAGE_SPEC

Create a notarized local release build:

./scripts/notarize_release.sh

Create or update the GitHub release, including managed support assets:

./scripts/github_release.sh --version X.Y.Z --notes-file /absolute/path/to/release-notes.md

The GitHub release script uploads:

• notarized app zip
• app zip checksum
• managed support manifest
• managed Python source runtime archive + checksum
• managed deno archive + checksum

It also republishes those managed support assets to the dedicated managed-support release channel so the app can pick up newer source-runtime / deno payloads without waiting for a new app build.

If you only want to refresh managed support payloads:

./scripts/publish_managed_support.sh

4. Manual Notarization (Reference)

If you need to run manual notarization steps instead of scripts/notarize_release.sh:

codesign --force --options runtime --timestamp --sign "Developer ID Application: <Name> (<TEAMID>)" "dist/Back Channel.app"
ditto -c -k --keepParent "dist/Back Channel.app" "dist/Back-Channel.zip"
xcrun notarytool submit "dist/Back-Channel.zip" --keychain-profile "<profile>" --wait
xcrun stapler staple "dist/Back Channel.app"
xcrun stapler validate "dist/Back Channel.app"

Usage

1. Enter source livestream URL.
2. Click Load Info to fetch and preview title/thumbnail/description excerpt.
3. Choose output format:
   • RTMP for push targets (rtmp://server/app/key)
   • HLS for local/served playlist output (/path/to/out.m3u8)
4. For RTMP, either:
   • fill Server URL + Stream Key, or
   • paste a full RTMP URL in Full RTMP URL (optional override)
5. Choose mode:
   • Stream Copy for lowest CPU on RTMP (Streamlink -> FFmpeg remux, best-effort passthrough)
   • Compatible for RTMP resync/transcode (Streamlink -> single FFmpeg resync/transcode, libx264 + aac, fixed GOP/CFR)
6. Click Start.
7. Use Status tab for parsed health/progress, and Advanced tab for raw console logs.

Repository Layout

• Sources/youtube-live-converter/: Swift app source
• scripts/: build, packaging, notarization, and release scripts
• website/: GitHub Pages site
• dist/: local build outputs

Notes

• The app captures source-tool (Streamlink or yt-dlp) and ffmpeg stderr logs in the UI.
• On process failure, it retries with exponential backoff (up to 30 seconds).
• For RTMP, Compatible uses Streamlink plus a single FFmpeg resync/transcode stage.
• Stream Copy may fail if target/container codec compatibility does not match. Use Compatible mode in that case.
• Runtime tool resolution prefers:
  • app-managed support components in ~/Library/Application Support/Back Channel/
  • bundled app resources in .app/Contents/Resources/bin
• End users do not need Homebrew, Python, Xcode command line tools, or manually installed runtimes.