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OptimFROG is a lossless audio codec with optional hybrid lossless/lossy encoding. It comes with a freeware (closed-source) command-line encoder/decoder and plugins for several players and processing front-ends, and an SDK to use in other applications. It is available for Windows, Linux, FreeBSD and MacOSX, all in both 32-bit and 64-bit versions. Encoders for its hybrid "DualStream" format, and for floating-point audio, are included in the distributions in separate executables.

OptimFROG is a codec that gives priority to compression size, sacrificing speed. Its highest presets compress to smaller file sizes than any other end-user codec, possibly except the (legacy/unmaintained) La. These presets are CPU intensive both for decoding and encoding, sometimes a 10x increase over the faster presets, where OptimFrog would compress about the speed of Monkey's Audio “Extra High” and achieve compression ratios like Monkey's “High”.[1] Positioning itself at, arguably, one extreme of the size/CPU load trade-off, it has a fairly small userbase - and unlike most notable codecs, there is apparently no 3rd party decoder available and no sign of ffmpeg reverse-engineering the format (like was done with TAK).


For an end-user considering OptimFROG as an audio format - likely due to its compression ratios, possibly also its hybrid mode - some of the following features are quite common among lossless codecs, while some are more scarce - in particular, the end of this list. To compare OFR with other lossless codecs, see HA Wiki's Lossless Codec Comparison.

  • Seekable and streaming playback.
  • Error handling. Audio checksum optional (use the --md5 option upon encoding, --check to verify it), but OFR can also check corruption without decoding (--verify), hence quicker than any decoding format. Decoder can continue through errors.
  • High-resolution audio support: apparently, any sampling rate that the WAVE format supports (4 GiHz), up to 32 bits per channel. Like WavPack but unlike most other formats, it also supports floating-point format (through a different executable included in the distribution).
  • Piping support for encoding, and support for RAW PCM input.
  • Tagging. (APEv2, or ID3 - see below.)
  • RIFF chunks supported for recreating also non-audio chunks of the original .wav files; by default, OptimFROG will restore to a .wav file bit-identical to the original.
  • Can read certain malformed .wav files; in particular, some hacks employed to fit more than the 4 GB size limitation into .wav files. (It is unclear what malformed .wav files will be recreated bit-identical.)
  • Like WavPack, but unlike most other encoders, it can create Windows self-extracting (.sfx) archives.
  • Hybrid lossy/lossless encoding supported. Like WavPack, but unlike most (every?) other end-user codecs, OptimFROG can decode both lossy and lossless streams together, to be maintained in the same library. A separate encoder is included in the distribution.


  • Currently there is no hardware supporting the format and software support is limited. The official encoder/decoder is closed-source (but a an official library can be used in third-party applications). Also the format has no official specification, and little is known about it.[2]
  • No multichannel support.
  • CPU intensive (slow) encoding and decoding, especially in the higher modes. Given that portable low-power devices are out of consideration as they cannot play the files anyway, speed might not be that much of a limitation with the power of modern computers. Still, users who consider playing OptimFrog files from a battery-powered laptop or tablet, might want to test battery life impact, especially since it varies over the settings.
  • Encoder has no provision of adding tags.

Because OptimFrog - like MP3 - can accommodate both APE tags and ID3, tagging ambiguity could be an issue: one application might not read another's tags. A user would likely want to stick to one tag format. Mp3tag, MusicBrainz Picard and foobar2000 will write APEv2 tags (at least by default). According to the website, EAC will write ID3v1.1 tags to .ofr files - and apparently there is no way for it to write APEv2 as the encoder has no switches for it (contrast to EAC with WavPack).

Software support

Some of the software cited at http://losslessaudio.org/Compatible.php has disappeared. One may still obtain the Kermit front-end from Archive.org. Most of the following should work:

  • foobar2000 (through plugin available at the OptimFROG website)
  • Winamp (through plugin available at the OptimFROG website)
  • XMPlay for Windows, BASS_OFR addon available at player's website.
  • XMMS (?)
  • dBPoweramp music converter
  • Mp3tag for tagging.
  • MusicBrainz Picard for tagging (no audio fingerprinting).


  1. Martijn van Beurden's lossless performance tests. Performance comparisons taken from version 4 and for CDDA audio; OptimFrog version tested 4.910b. Later versions introduced new presets, possibly altering the speed/compression trade-off.
  2. Multimediawiki's OptimFROG entry. It is known that the format has been through a change; but, the decoder does support old OptimFROG files.