5.0

• Fixed all issues with FFmpeg 6.1 which is now the minimum requirement
• Fixed av1 decoding
• Added HDR10+ and DolbyVision metadata
• Fixed audio decoding that could otherwise get stuck in an infinite loop on certain files
• Fixed framerate in Avisynth when using VFR=>CFR mode
• Dropped VapourSynth API3 support
• Indexer now has a configurable progress update interval
• Alpha planes are now correctly marked as being full range
• The full set of demuxer options can now be passed using the FFMS2 API
• Now sets channel layout in Avisynth+
• Removed the unfixable and always broken rffmode from Avisynth source

5.0-RC4

Probably the last RC
A large number of seeking fixes
RFF mode removed since it was never correct anyway

5.0-RC3

Compiled with a more full features FFmpeg this time.
Known issues:

• Interlaced h264 broken
• rff handling broken
• vc1 probably a bit broken

5.0-RC2

Fix delay calculation for sliced thread
Fix frame drops/duplication in CFR mode when forcing a multiple of the source framerate

5.0-RC1

Update changelog and version number

2.40

• 2.40
  • Avisynth+ linux support (qyot27)
  • Added LastEndTime track property to make it possible to take the last frame's duration into account (Myrsloik)
  • Removed several deprecated functions and enums from the API (Myrsloik)
  • No longer assumes sub 1 fps framerates are invalid (Myrsloik)
  • Added support for floating point format output in VapourSynth and Avisynth+ (Myrsloik)
  • Fixed issue with dropped/repeated frames in vc1 with multiple b-frames after seeking (Myrsloik)
  • Fixed issue with dropped/repeated frames in h264 when the reorder buffer size is too small (Myrsloik)
  • Improved seeking in mpeg and mpegts streams (Myrsloik)
  • Added rgb(a)p and several additional formats as output to Avisynth+ (Myrsloik)
  • Added VP9 support (Daemon404)
  • Fixed incorrectly reporting the output as limited range when it's in fact unknown and likely to be full range (Myrsloik)
  • Added mastering display metadata output (Myrsloik)
  • VapourSynth source now defaults to not outputting alpha (Myrsloik)
  • Removed the now unused demuxer, dumpmask, audiofile and utf8 arguments from the source filters (Myrsloik)
  • Removed ability to dump audio tracks (Myrsloik)
  • Fixed incorrect colorimetry metadata reported when converting the output to another colorspace (Myrsloik)
  • Sources now simply reference the index instead of copying large parts of it (Myrsloik)
  • Use new FFmpeg decoding API (Myrsloik)
  • Fixed several bugs in output format selection (Myrsloik)
  • FFMSIndex will now properly error out with invalid arguments (Myrsloik)
  • Add rotation metadata export (Myrsloik)
  • Add stereoscopic metadata export (Myrsloik)
  • Created new Visual Studio 2017 projects (Myrsloik)
  • Removed old mingw version support (Myrsloik)
  • Removed support for old FFmpeg versions (Myrsloik)
  • Removed libav support (Myrsloik)
  • Discontinuous Timestamp Support (Daemon404)
  • Add FFMS_Deinit (Daemon404)
  • Fix mid-stream parameter changes (Daemon404)
  • Fix decoding H.264 PAFF files with one field per packet (Daemon404)
  • Fix delay calculations for H.264 PAFF files (Daemon404)
  • Fix frame rate calculation for fields with one field per packet (Daemon404)

2.23.1

• Updated FFmpeg APIs used (Daemon404)
• Added new API that can read/write indexes to a memory buffer (Daemon404)
• Added support for high bitdepth output in Avisynth+ (Myrsloik)
• vapoursource: Add nfMakeLinear flag to better performance in most cases (Myrsloik)
• Remove bad colorspace matrix guessing for YUV (Myrsloik)
• Tell libavformat to discard packets we don't want (Daemon404)
• Restore original FFCopyrightInfringement behavior (Myrsloik)
• Make FFMS_Init threadsafe (Daemon404)
• Support latest libav* APIs (Daemon404)

2.22

• Fix possible off by 1 frame until first seek issue introduced in 2.21 (Myrsloik)
• avisynth: Make FFMS2 a shorter alias for FFmpegSource2 to save some typing (Myrsloik)
• avisynth: Moved all source functions in ffms2.avsi into the actual plugin (Myrsloik)
• avisynth: Use 2.6 RC API and add output support for all new colorspaces (Myrsloik)
• vapoursource: Fix swapped RGB channels bug introduced in 2.21 (Myrsloik)
• swscale: Drop pointless and slow bitexact flag from resizer settings (kodabb)
• Add support for files with gaps between the audio packets (Plorkyeran)

2.21

Mostly maintenance bug fixes and a much newer FFmpeg version, but there's also new API stuff for indexing files to support files with more than 32 tracks. The non-FFmpeg Matroska, MPEG-TS and OGM parsers have been dropped since these days libavformat's are good enough (and sometimes better).

• Add missing constants for log levels (Myrsloik)
• Fix bad decoder flush that discards the palette of raw video (Myrsloik)
• Remove the SWScale function from Avisynth since SWScale is useless (Myrsloik)
• Fix common framerate correction (Myrsloik)
• vapoursource: The framerate and frame durations are now normalized (Myrsloik)
• vapoursource: Add support for outputting the alpha channel too (Myrsloik)
• vapoursource: Fix resizer selection so bicubic isn't always used (Myrsloik)
• vapoursource: Set chroma location and full colorspace information (Myrsloik)
• Add support for indexing files with more than 32 tracks and the possibility to skip indexing of video tracks (Myrsloik)
• The Avisynth plugin now sets all per frame variables in all modes to avoid ugly and slow FFInfo() errors (Myrsloik)
• vapoursource: Fix crash on single frame files (Myrsloik)
• Remove the Matroska and Haali demuxers (qyot27, Plorkyeran)
• Fix adjustments for positive audio delay (tophf)
• Don't try to index video tracks in unsupported formats (Daemon404)
• Don't use scientific notation in timecode files (Daemon404)
• Fix utf8 support in FFVideoSource (nixxquality)
• Improve handling of files where only some packets have timestamps (Plorkyeran)
• Fix memory leaks in the VapourSynth error handling (Plorkyeran)

ICL version is typically ~10% faster on Intel CPUs, but is less tested.

FFMS 2.20

• Add support for Opus in MKV when ffmpeg/libav are built with libopus (qyot27)
• vapoursource: Provide _AbsoluteTime metadata (Daemon404)
• Fix a pile of small things found by Coverity (Daemon404)
• Add support for HEVC in MKV (qyot27)
• Fix infinite loop on garbage data at the beginning of AAC files (Plorkyeran)
• Deal with the never-ending bitrot from FFmpeg/Libav API changes (Daemon404, Plorkyeran)
• Make indexes not arch-specific and trivially smaller (Plorkyeran)
• Fix bug where the first b-frame was replaced with the frame before it with open-gop h.264 (Plorkyeran)
• Fix seeking issues with open-gop h.264 (Plorkyeran)
• Fix corruption when seeking in interlaced h.264 (Plorkyeran)
• Add support for multiple frames per audio packet as FFmpeg seems to have started doing that (Plorkyeran)
• Fix seeking in Y4M files (Plorkyeran)
• Fix dumping audio while indexing files
• Add support for Matroska files with extremely large CodecPrivate sections
• Speed up indexing Matroska files a bit

The ICL version is approximately 10% faster on Intel CPUs, while the MSVC version is probably faster on AMD CPUs (but I do not have any available to test with).