Apps similar to JustStream include GogglePlayer. Other options are CastPanda. Between them they cover Mac and Windows.
Windows app that streams video files, your desktop, webcams and URLs to DJI Goggles, DLNA and UPnP devices, Google Cast, a web browser or a second screen. Also saves converted video to an SD card. Transcoding, split-audio sync, subtitles. No ads, no telemetry.
Norway
CastPanda streams almost any video file from your Mac to Apple TV, AirPlay 2 smart TVs and Chromecast. MKV, AVI, WebM and more play straight away, with formats the TV can't handle converted as they play. Supports subtitles (.srt, .ass, .vtt), audio track switching, 5.
