MKVToolNix 9.4.1 is dubbed “Black Rain,” and, according to the release notes, it looks like it adds many improvements to the mkvmerge tool, a component that lets users merge MKV files with different audio, video, or subtitle streams. For example, the HEVC parser, MP4 reader, and AAC reader received various fixes. Moreover, the muxing operation will no longer be aborted when attempting to use ???sync values of several minutes with specific container formats, and an invalid memory access was addressed. However, it appears that a bug was present in the MKVToolNix 9.4.1, so the developer was quick to fix it and release a new build.