Speedup the Rendering

[cvelasco88]

Please include the following information.

1. Flowblade version (Help->About): 2.4.0
2. MLT version (Help->Runtime Environment): 6.20.0
3. Your distribution (Ubuntu, Debian, Mint etc.): Ubuntu 20.04
4. If possible, try to provide step-by-step instructions on how to reproduce the issue. From developer point of view this is the easieast way to understand what is happening.:

This is as a suggestion of improvement
I use to render some videos with only ONE track of Video and ONE track of Audio and i just would like to enjoy the same speed than i have when i do ffmpg commands. So i ask/suggest for a way to detect this conditions (1 video, N audio and improve the rendering just cutting and joining the video on the time marks, then add/replace the right processed audio on it)

[jliljebl]

This is the no-encoding workflow where video and audio streams data are combined without with re-encoding the stream.

There are some applications that provide an GUI for doing this and use ffmpeg as backend, but feature is not easily addable for full video editor like Flowblade, because all code in the application and MLT assume that video data is decoded and then encoded to create output. So this feature unfortunately wont be added.