Current compatibility:

File format
    Protracker MOD modules.
    May support XM in the future.

MOD:
    Supports 4, 8, 16, 24, 32, 48 channel modules right now. Does not support
    arbitrary channel counts yet.

    If the channel did not convert properly, use openmpt to save it with
    the correct amount of channels.

    Playback may not be 100% accurate to protracker, or anything really.

Effects:
    Implemented
        0xx Arpeggio
        1xx, 2xx Portamento
        3xx, 5xx Tone portamento
        4xx, 6xx Vibrato
        8xx (Subject to chip-specific limitations) Set panning
        9xx Sample offset (Subject to chip-specific limitations)
        Axx, 5xx, 6xx Volume slide
        Bxx Position jump
        Cxx Volume
        Dxx Pattern break
        E1x, E2x Fine portamento
        E5x Fine tune
        E6x Pattern loop
        E8x Set panning (see above)
        E9x Retrigger
        EAx, EBx Fine volume slide
        ECx, note cut
        EDx, Note delay
        EEx, pattern delay (Not tested yet)
        Fxx, Speed/tempo
    Not implemented
        6xx Tremolo (planned)
        E3x Glissando
        E4x Vibrato waveform (currently sine only)
        E7x Tremolo waveform
        EFx Invert loop (Chip limitations, may work for C352?)

Chip notes: OPL4 (YMF278B) Max 24 channels. Max sample length: 65535 Max loop length: same. Supports 8/12/16 bit samples.

    Converter only supports 8-bit samples at this point.

    Should support all possible Amiga frequencies. Currently using PAL values as this seem to sound
    best with the modules I have.

    Does not support one-off samples, all samples are looping internally. A 4 byte buffer is reserved
    at the end of the sample for this purpose. This reduces the max sample length.

    The OPL4 has support for hardware envelopes, this feature is not used by the converter at this point.

    Sample metadata is stored in the data block. Sample offsets are stored by adding extra entries.
    This limits the song to 96 unique sample offsets. (sample + 9xx parameter).
    Also, looping samples with an offset further than the loop point will not loop. They might even
    cause a high frequency beep.

    Has an attenuation register, the maximum level does not silence the sample completely.
    Mod volumes are roughly translated to attenuation levels for this register
    Effect C00 also sets the pan temporarily to 0 in order to silence the sample. This may not happen
    when restarting the song loop though. Best to add a 800 effect at the loop point if you want to ensure
    the sample is muted after the song loop.

    Panpot has range of 15 possible values. Low nibble of 8xx effects is ignored.
    A value of 0 mutes the sample completely.

    TL;DR:
        Sample length slightly reduced for non-looping samples
        Sample offset loops may not work
        Pan range 0x10-0xF0, 0x00 mutes the sample, low nibble ignored.
        Volumes may be a little off, especially around higher values.

YMZ280B
    Considered for inclusion.

    Max 8 channels.
    Max sample length: 16m
    Max loop length: same
    Supports 8/16-bit PCM samples, and 4-bit ADPCM.

    Frequency range is limited, 0-88200 Hz in 512 steps for PCM, 0-44100 in 256 steps for ADPCM.
    This means 172 Hz per step, which might be noticable for low frequency samples...

    Would support sample offset though.

To do: Support all effects... More cleanups... Implement XM support...