Common questions and problems

High memory usage

If you have "Burn In" subtitles enabled, this is probably the cause. The "overlay" filter can use huge amounts of memory as reported by Zeid164.

Too many packets buffered for output stream 0:1.

You need to increase the Max Musing Queue Size, command line equivalent: -max_muxing_queue_size 1024

HDR colors washed out

This is generally due to the color space not being transferred correctly. Possibly a bt2020 video was turned into a bt709. If it is happening with FastFlix please raise an issue with the MediaInfo text of the input and output video and the command FastFlix generated, would really help in fixing it fast or figuring out why it is behaving that way.

Unrecognized option ...

You probably need to update FFmpeg.