Due to losslesscut using chromium's html5 video tag which only supports certain container formats and codecs, we currently need to "convert to supported format" when trying to open exotic formats or codecs. This could be improved with the help of ffmpeg.

Workarounds

Compile custom electron

• https://github.com/electron/build-tools
• Support for proprietary codecs electron/electron#633
• Provide ffmpeg.so file that plays all common videos electron/electron#9534

Convert to supported format

Currently it's possible to cut those files by first using the File -> Convert to supported format (slow) function, however this is a re-encoding (although fast) of the whole file, just to be able to view it in the HTML5 video player (note that the original and cut versions will not be re-encoded and are still lossless.)

Improve current proxy/dummy code

Currently a <canvas> element is used, and ffmpeg will stream low-resolution jpeg images to that canvas.

Drawbacks:

• Slow, laggy, low resolution, low fps
• No audio

This could be improved:

• MediaSource API & https://www.electronjs.org/docs/latest/tutorial/message-ports
• Web Audio API: https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_API
• https://github.com/strukturag/libde265.js
• https://stackoverflow.com/questions/55376781/seeking-with-ffmpeg-at-the-end-of-an-rtsp-stream
• https://stackoverflow.com/questions/61672575/rtsp-to-webrtc-live-video-streaming
• https://stackoverflow.com/questions/41965793/rtsp-h-264-in-google-chrome-browser
• https://github.com/Streampunk/beamcoder
• https://github.com/GleasonK/WebRTC-YouTubeTogether
• https://phoboslab.org/log/2013/09/html5-live-video-streaming-via-websockets
• https://github.com/phoboslab/jsmpeg

Related

• H.265 video playback webtorrent/webtorrent-desktop#561
• Support more audio and video codecs webtorrent/webtorrent-desktop#1389

Electron (Chromium) might never support h265

It seems like Chrome and most other browsers are not going to be supporting H265 as it stands now, and since we are using Chromium (Electron), this will be a problem.
It might be possible to enable a flag to enable H265 decoding, but it requires some modding of electron.

• https://stackoverflow.com/questions/36382568/h-265-hevc-web-browser-support
• Building with an alternative libffmpeg electron/libchromiumcontent#198

Update: Chromium now supports h265 (hardware decoding only)