: Keep track of key (on/off) status of MIDI notes and control switches. This isn't generally recommended, but may occasionally be useful to deal with quirky controllers sending note- or control-ons without corresponding off messages.
: Enable MIDI output. Add "2" for a second pair of MIDI ports to be used, e.g., for controller feedback. See Sections *MIDI Output* and *Secondary MIDI Ports*.
: Set the configuration file name. Default: Taken from the MIDIZAP_CONFIG_FILE environment variable if it exists, or ~/.midizaprc if it exists, /etc/midizaprc otherwise. See Section *Configuration File*.
: Enable various debugging options: r = regex (print matched translation sections), s = strokes (print the parsed configuration file in a human-readable format), k = keys (print executed translations), m = midi (MIDI monitor, print all recognizable MIDI input), j = jack (additional Jack debugging output). Just `-d` enables all debugging options. See Section *Basic Usage*.
The midizap program translates Jack MIDI input into X keystrokes, mouse button presses, scroll wheel events, or, as an option, MIDI output. It does this by matching the `WM_CLASS` and `WM_NAME` properties of the window that has the keyboard focus against the regular expressions for each application section in its configuration (midizaprc) file. If a regex matches, the corresponding set of translations is used. Otherwise the program falls back to a set of translations in a default section at the end of the file, if available.
The midizaprc file is just an ordinary text file which you can edit to configure the program. An example.midizaprc file containing sample configurations for some applications is included in the sources. Also, in the examples directory you can find some more examples of configuration files for various purposes.
midizap provides you with a way to hook up just about any MIDI controller to your favorite multimedia applications, like digital audio workstation (DAW) programs, as well as audio and video editors. The MIDI output option is useful if the target application supports MIDI, but can't work directly with your controller because of protocol incompatibilities. In particular, you can use midizap to turn pretty much any MIDI controller with enough faders and buttons into a Mackie-compatible mixing device for DAW programs. Another common use case is video editing software, which rarely offers built-in MIDI controller support. midizap allows you to map the faders, encoders and buttons of your MIDI controller to corresponding keyboard commands of your video software for cutting, marking, playback, scrolling and zooming.
In other words, as long as the target application can be controlled with simple keyboard shortcuts and/or MIDI commands, chances are that midizap can make it work with your controller at least to some extent.
First, make sure that you have the required dependencies installed. The program needs a few X11 libraries and Jack. And of course you need GNU make and gcc (the GNU C compiler). On Ubuntu and other Debian-based systems you should be able to get everything that's needed by running this command:
Then just run `make` and `sudo make install`. This installs the example.midizaprc file as /etc/midizaprc, and the midizap program and the manual page in the default install location. Usually this will be under /usr/local, but the installation prefix can be changed with the `prefix` variable in the Makefile. Also, package maintainers can use the `DESTDIR` variable as usual to install into a staging directory for packaging purposes.
After installation the system-wide default configuration file will be in /etc/midizaprc, where the program will be able to find it. We recommend copying this file to your home directory, renaming it to .midizaprc:
The ~/.midizaprc file, if it exists, takes priority over /etc/midizaprc, so it becomes your personal default midizap configuration. The midizaprc file included in the distribution is really just an example; you're expected to edit this file to adjust the bindings for the MIDI controllers and the applications that you use. (If you create new configurations which might be useful for others, please consider submitting them so that they can be included in future releases.)
It is also possible to specify the configuration file to be used, by invoking midizap with the `-r` option on the command line, e.g.: `midizap -r myconfig.midizaprc`. This is often used with more specialized configurations dealing with specific applications or MIDI controllers.
**NOTE:** The program automatically reloads the midizaprc file whenever it notices that the file has been changed. Thus you can edit the file while the program keeps running, and have the changes take effect immediately without having to restart the program. When working on new translations, you may want to run the program in a terminal, and employ some or all of the debugging options explained below to see exactly how your translations are being processed.
The midizap program is a command line application, so you typically run it from the terminal, but of course it is also possible to invoke it from your desktop environment's startup files once you've set up everything to your liking.
midizap uses [Jack][] for doing all its MIDI input and output, so you need to be able to run Jack and connect the Jack MIDI inputs and outputs of the program. While it's possible to do all of that from the command line as well, we recommend using a Jack front-end and patchbay program like [QjackCtl][] to manage Jack and to set up the MIDI connections. In QJackCtl's setup, make sure that you have selected `seq` as the MIDI driver. This exposes the ALSA sequencer ports of your MIDI hardware and other non-Jack ALSA MIDI applications as Jack MIDI ports, so that they can easily be connected to midizap.
(Here and in the following, we're assuming that you're using Jack1. Jack2 works in a very similar way, but may require some more fiddling; in particular, you may have to use [a2jmidid][] as a separate ALSA-Jack MIDI bridge in order to have the ALSA MIDI devices show properly as Jack MIDI devices.)
Having that set up, start Jack, make sure that your MIDI controller is connected, and try running `midizap` from the command line (without any arguments). In QJackCtl, open the Connections dialog and activate the second tab named "MIDI", which shows all available Jack MIDI inputs and outputs. On the right side of the MIDI tab, you should now see a client named `midizap` with one MIDI input port named `midi_in`. That's the one you need to connect to your MIDI controller, whose output port should be visible under the `alsa_midi` client on the left side of the dialog.
To test the waters, you can hook up just about any MIDI keyboard and give it a try with the default section in the distributed midizaprc file, which contains some basic translations for mouse and cursor key emulation. Here is the relevant excerpt from that section:
We refer to Section *Translation Syntax* below for a discussion of the syntax being used here, but it should be fairly obvious that these translations map the white keys of the middle octave (MIDI notes `C5` thru `B5`) to some mouse buttons and cursor commands. Switch the keyboard focus to some window with text in it, such as a terminal or an editor window. Pressing the keys C, D and E should click the mouse buttons, while F thru B should perform various cursor movements. Also, moving the modulation wheel (`CC1`) on your keyboard should scroll the window contents up and down.
One useful feature is that you can invoke the program with various debugging options to get more verbose output as the program recognizes events from the device and translates them to corresponding mouse actions or key presses. E.g., try running `midizap -drk` to have the program print the recognized configuration sections and translations as they are executed. Now press some of the keys and move the modulation wheel. You should see something like:
It goes without saying that these debugging options will be very helpful when you start developing your own bindings. The `-d` option can be combined with various option characters to choose exactly which kinds of debugging output you want; `r` ("regex") prints the matched translation section (if any) along with the window name and class of the focused window; `s` ("strokes") prints the parsed contents of the configuration file in a human-readable form whenever the file is loaded; `k` ("keys") shows the recognized translations as the program executes them, in the same format as `s`; `m` ("MIDI") prints *any* MIDI input, so that you can figure out which MIDI tokens to use for configuring the translations for your controller; and `j` adds some debugging output from the Jack driver. You can also just use `-d` to enable all debugging output. (Most of these options are also available as directives in the midizaprc file; please check the distributed example.midizaprc for details.)
Have a look at the distributed midizaprc file for more examples. Most of the other translations in the file assume a Mackie-like device with standard playback controls and a jog wheel. Any standard DAW controller which can be switched into Mackie mode should work with these out of the box. In any case, you may now want to start editing the configuration, to remove entries that you don't need, and to make the translations work with your controller and favorite applications.
As already mentioned, the midizap program can also be made to function as a MIDI mapper which translates MIDI input to MIDI output. MIDI output is enabled by running the program as `midizap -o`. This equips the Jack client with an additional MIDI output port named `midi_out` (visible on the left side of QJackCtl's Connection window).
The example.midizaprc file comes with a sample configuration in the special `[MIDI]` default section for illustration purposes. This section is only active if the program is run with the `-o` option. It allows MIDI output to be sent to any connected applications, no matter which window currently has the keyboard focus. This is probably the most common way to use this feature, but of course it is also possible to have application-specific MIDI translations, in the same way as with X11 key bindings. In fact, you can freely mix mouse actions, key presses and MIDI messages in all translations.
You can try it and test that it works by running `midizap -o`, firing up a MIDI synthesizer such as [FluidSynth][] or its graphical front-end [Qsynth][], and employing QjackCtl to connect its input it to midizap's output port. In the sample configuration, the notes `C4` thru `F4` in the small octave have been set up so that you can operate a little drumkit, and a binding for the volume controller (`CC7`) has been added as well. The relevant portion from the configuration entry looks as follows:
Note the `-10` suffix on the output messages in the above example, which indicates that output goes to MIDI channel 10. In midizaprc syntax, MIDI channels are 1-based, so they are numbered 1..16, and 10 denotes the GM (General MIDI) drum channel.
E.g., the input note `C4` is mapped to `C3-10`, the note C in the third MIDI octave, which on channel 10 will produce the sound of a bass drum, at least on GM compatible synthesizers like Fluidsynth. The binding for the volume controller (`CC7`) at the end of the entry sends volume changes to the same drum channel (`CC7-10`), so that you can use the volume control on your keyboard to dial in the volume on the drum channel that you want. The program keeps track of the values of both input and output controllers on all MIDI channels internally, so with the translations above all that happens automagically.
Besides MIDI notes and control change (`CC`) messages, the midizap program also recognizes program change (`PC`) and pitch bend (`PB`) messages, which should cover most common use cases; see below for details. Other messages (in particular, aftertouch and system messages) are not supported right now, but may be added in the future.
After the first line with the section header, each subsequent line indicates a translation rule belonging to that section. Note that we used `<X..Y>` here to indicate ranges, and `output` as a placeholder for the output sequence. We'll describe each of these elements in much more detail below.
Also note that the `#` character at the beginning of a line and after whitespace is special; it indicates that the rest of the line is a comment, which is skipped by the parser. Empty lines and lines containing nothing but whitespace are also ignored.
Each `[name] regex` line introduces the list of MIDI message translations for the named translation class. The name is only used for debugging output, and needn't be unique. The following lines indicate what output should be produced for the given MIDI messages.
When focus is on a window whose class or title matches the regular expression `regex`, the following translation class is in effect. An empty regex for the last class will always match, allowing default translations. Any output sequences not bound in a matched section will be loaded from the default section if they are bound there.
The left-hand side (first token) of each translation denotes the MIDI message to be translated. MIDI messages are on channel 1 by default; a suffix of the form `-<1..16>` can be used to specify a different MIDI channel. E.g., `C3-10` denotes note `C3` on MIDI channel 10.
Note messages are specified using the customary notation (note name `A..G`, optionally followed by an accidental, `#` or `b`, followed by the MIDI octave number. Note that all MIDI octaves start at the note C, so `B0` comes before `C1`. By default, `C5` denotes middle C. Enharmonic spellings are equivalent, so, e.g., `D#` and `Eb` denote exactly the same MIDI note.
We will go into most of the other syntactic bits and pieces of MIDI message designations later, but it's good to have the following grammar in EBNF notation handy for reference:
Case is ignored, so `CC`, `cc` or even `Cc` are considered to be exactly the same token by the parser. Numbers are always integers in decimal. The meaning of the first number depends on the context (octave number for notes, controller or program number in the range 0..127 for other messages). This can optionally be followed by a number in brackets, denoting a nonzero step size. Also optionally, the suffix with the third number (after the dash) denotes the MIDI channel in the range 1..16; otherwise the default MIDI channel is used (which is always 1 on the left-hand side, but can be set on the right-hand side with `CH`). The optional incr flag at the end of a token indicates an "incremental" translation which responds to numeric (up/down) value changes rather than key presses, cf. *Key vs. Incremental* below.
A note on the octave numbers in MIDI note designations is in order here. There are various different standards for numbering octaves, and different programs use different standards, which can be rather confusing. E.g., there's the ASA (Acoustical Society of America) standard where middle C is C4, also known as "scientific" or "American standard" pitch notation. At least two other standards exist specifically for MIDI octave numbering, one in which middle C is C3 (so the lowest MIDI octave starts at C-2), and zero-based octave numbers, which start at C0 and have middle C at C5. There's not really a single "best" standard here, but the latter tends to appeal to mathematically inclined and computer-savvy people, and is also what is used by default in the midizaprc file.
However, if you prefer a different numbering scheme then you can easily change this by specifying the desired offset for the lowest MIDI octave with the special `MIDI_OCTAVE` directive in the configuration file. For instance:
This is useful, in particular, if you use some external MIDI monitoring software to figure out which notes to put into your midizaprc file. To these ends, just check how the program prints middle C, and adjust the `MIDI_OCTAVE` offset in your midizaprc file accordingly. (Note that midizap's built-in MIDI monitoring facility always prints out MIDI notes using the `MIDI_OCTAVE` offset that is in effect. Thus in this case the printed note tokens will always be in exactly the form that is to be used in the midizaprc file, no matter what the `MIDI_OCTAVE` offset happens to be.)
Input MIDI messages can generally be processed in two different ways, "key mode" and "incremental mode".
*Key mode* is the default mode and is available for all message types. In this mode, MIDI messages are processed as if they were keys on a computer keyboard, i.e., they can be "on" ("pressed") or "off" ("released"). For notes, a nonzero velocity means "pressed", zero "released". Similarly, for control changes any nonzero value indicates "pressed". Same goes for pitch bends, but in this case 0 denotes the center value (considering pitch bend values as signed quantities in the range -8192..8191), and any nonzero (positive or negative) value means "pressed", while 0 (the center value) means "released". Finally, while program changes don't actually come in "on"/"off" pairs, they are treated in the same key-like fashion, assuming that they are "pressed" and then "released" immediately afterwards.
*Incremental mode* is only available with `CC` (control change) and `PB` (pitch bend) messages. In this mode, the actual *amount* of change in the value of the message (increment or decrement, a.k.a. "up" or "down") is being processed rather than the on/off state. Incremental mode is indicated with a special suffix on the message token which indicates the direction of the change which the rule should apply to: increment (`+`), decrement (`-`), or both (`=`).
Incremental mode usually keeps track of changes in the *absolute* value of a control. However, it's also possible to deal with *relative* controllers. (These are sometimes also called "incremental." To avoid the confusion with incremental-mode processing, we stick to the term "relative" here.) The most common case of these are the (endless) rotary encoders and jog wheels you find on many DAW controllers. These emit special *sign bit* values, where a value <64denotesanincrement(usuallyrepresentingclockwiserotation),andavalue> 64 a decrement (counter-clockwise rotation). The actual amount of change is in the lower 6 bits of the value.
In the message syntax, these kinds of controls are indicated by using the suffix `<`, `>` and `~` in lieu of `-`, `+` and `=`, respectively. Note that these suffixes are only used with `CC` messages.
Each MIDI message may have at most one translation associated with it in each translation section, so that translations are determined uniquely. MIDI messages with different MIDI channels count as different messages, however, as do messages processed in different modes. Thus, `CC` and `PB` messages may have both key- and incremental-mode translations associated with them, in which case the former will be executed before the latter.
The right-hand side of a translation (i.e., everything following the first token) is a sequence of one or more tokens, separated by whitespace, indicating either MIDI messages or X11 keyboard and mouse events to be output.
Let's look at keyboard and mouse output first. It consists of X key codes (symbolic constants prefixed with `XK_` from the /usr/include/X11/keysymdef.h file) with optional up/down indicators, or strings of printable characters enclosed in double quotes. Also, there are some special keycodes to denote mouse button (`XK_Button_1`, `XK_Button_2`, `XK_Button_3`) and scroll wheel (`XK_Scroll_Up`, `XK_Scroll_Down`) events. Sequences may have separate press and release sequences, separated by the special word `RELEASE`.
Examples:
~~~
C5 "qwer"
D5 XK_Right
E5 XK_Alt_L/D XK_Right
F5 "V" XK_Left XK_Page_Up "v"
G5 XK_Alt_L/D "v" XK_Alt_L/U "x" RELEASE "q"
~~~
Any keycode can be followed by an optional `/D`, `/U`, or `/H` flag, indicating that the key is just going down (without being released), going up, or going down and being held until the "off" event is received.
So, in general, modifier key codes will be followed by `/D`, and precede the keycodes they are intended to modify. If a sequence requires different sets of modifiers for different keycodes, `/U` can be used to release a modifier that was previously pressed with `/D`.
Key-mode MIDI messages translate to separate press and release sequences. At the end of the press sequence, all down keys marked by `/D` will be released, and the last key not marked by `/D`, `/U`, or `/H` will remain pressed. The release sequence will begin by releasing the last held key. If keys are to be pressed as part of the release sequence, then any keys marked with `/D` will be repressed before continuing the sequence. Keycodes marked with `/H` remain held between the press and release sequences.
Incremental-mode `CC` (control change) and `PB` (pitch bend) messages are treated differently. Instead of providing separate press and release sequences, the output of such translations is executed whenever the controller increases or decreases, respectively. At the end of such sequences, all down keys will be released. For instance, the following translations output the letter `"a"` whenever the volume controller (`CC7`) is increased, and the letter `"b"` if it is decreased. Also, the number of times one of these keys is output corresponds to the actual change in the controller value. (Thus, if in the example `CC7` increases by 4, say, `"a"` will be output 4 times.)
Incremental-mode relative `CC` messages are treated in an analogous fashion, but in this case the increment or decrement is determined directly by the input message. For instance, the jog wheel on the Mackie MCU is of this kind, so it can be processed as follows, using `<` and `>` in lieu of `-` and `+` as the suffix of the `CC` message:
Incremental `CC` and `PB` messages can also have a *step size* associated with them, which enables you to downscale controller and pitch bend changes. The default step size is 1 (no scaling). To change it, the desired step size is written in brackets immediately after the message token, but before the increment suffix. Thus, e.g., `CC1[2]+` denotes a sequence to be executed once whenever the controller increases by an amount of 2. As another (more useful) example, `PB[1170]` will give you 7 steps up and down, which is useful to emulate a shuttle wheel with the pitch bend wheel available on many MIDI keyboards. For instance, we might map this to the `"j"` and `"k"` keys used to control the playback speed in various video editors as follows:
Most of the notations for MIDI messages on the left-hand side of a translation rule also carry over to the output side, in order to translate MIDI input to MIDI output. As already discussed in Section *MIDI Output* above, you need to invoke the midizap program with the `-o` option to make this work. (Otherwise, MIDI messages in the output translations will just be silently ignored.)
The output sequence can involve as many MIDI messages as you want, and these can be combined freely with keypress events in any order. There's no limitation on the type or number of MIDI messages that you can put into a translation rule.
Note that on output, the `+-<>` suffixes aren't supported, because the *input* message determines whether it is a key- or incremental-mode of event, and which direction it goes in the latter case.
For key-mode inputs, such as a note or a non-incremental control change message, the corresponding "on" or "off" event is generated for all MIDI messages in the output sequence, where the "on" value defaults to the maximum value (127 for controller values, 8191 for pitch bends). Thus, e.g., the following rule outputs a `CC80` message with controller value 127 each time middle C (`C5`) is pressed (and another `CC80` message with value 0 when the note is released again):
It is also possible to specify a step size in this case, which explicitly sets the value for the "on" state. For instance, the following variation of the rule above produces a `CC80` message with value 64 (rather than the default "on" value of 127) whenever the MIDI note `C5` is pressed:
On the left-hand side of a translation, there are two additional suffixes `=` and `~` for incremental `CC` and `PB` messages which are most useful with pure MIDI translations, which is why we deferred their discussion until now. If the increment and decrement sequences for these messages are the same, the `=` suffix can be used to indicate that this sequence should be output for both increments and decrements. For instance, to map the modulation wheel (`CC1`) to the volume controller (`CC7`):
The `~` suffix can be used to denote relative controllers in output messages, too. E.g., to translate a standard (absolute) MIDI controller to a relative encoder value, you might use a rule like:
~~~
CC48= CC16~
~~~
Specifying step sizes on the right-hand side of incremental translations works as well, but scales the values *up* rather than down. This is most commonly used when scaling up controller values to pitch bends, which cover 128 times the range of a controller:
Another possible use is to scale controller values *both* down and up with a combination of step sizes on the left- and right-hand sides, to achieve (an approximation of) a rational scaling factor (2/3 in this example):
~~~
CC1[3]= CC1[2]
~~~
There are two other special tokens on the output side, `CH` which selects the default MIDI channel for output, and `SHIFT` which is used for processing shift state. We'll discuss the latter in its own section below. The `CH` token, which is followed by a MIDI channel number in the range 1..16, doesn't actually generate any MIDI message, but merely sets the default MIDI channel for subsequent MIDI messages in the same output sequence. This is convenient if multiple messages are output to the same MIDI channel. For instance, the sequence `C5-2 E5-2 G5-2`, which outputs a C major chord on MIDI channel 2, can also be abbreviated as `CH2 C5 E5 G5`.
## Shift State
The special `SHIFT` token toggles an internal shift state, which can be used to generate alternative output for certain MIDI messages. Please note that, like the `CH` token, the `SHIFT` token doesn't generate any output by itself; it merely toggles the internal shift bit which can then be queried in other translations to distinguish between shifted and unshifted bindings for the same input message.
To these ends, there are two additional prefixes which indicate the shift status in which a translation is active. Unprefixed translations are active only in unshifted state. The `^` prefix denotes a translation which is active only in shifted state, while the `?` prefix indicates a translation which is active in *both* shifted and unshifted state.
Many DAW controllers have some designated shift keys which can be used for this purpose, but the following will actually work with any key-style MIDI message. E.g., to bind the shift key (`A#5`) on a Mackie controller:
Note the `?` prefix indicating that this translation is active in both unshifted and shifted state, so it is used to turn shift state both on and off, giving a "Caps Lock"-style of toggle key. If you'd rather have an ordinary shift key which turns on shift state when pressed and immediately turns it off when released again, you can do that as follows:
Having set up the translation for the shift key itself, we can now indicate that a translation should be valid only in shifted state with the `^` prefix. This makes it possible to assign different functions, e.g., to buttons and faders which depend on the shift state. Here's a typical example which maps a control change to either Mackie-style fader values encoded as pitch bends, or incremental encoder values:
**NOTE:** To keep things simple, only one shift status is available in the present implementation. Also, when using a shift key in the manner described above, then its status is *only* available internally to the midizap program; the host application never gets to see it. If your host software does its own handling of shift keys (as most Mackie-compatible DAW software does), then it's usually more convenient to simply pass those keys on to the application and have it take care of them.
However, midizap's internal shift status feature may come in handy if your controller simply doesn't have enough buttons and faders to control all the essential features of your target application. In this case the internal shift feature makes it possible to (almost) double the amount of controls available on the device. For instance, you can emulate a Mackie controller with both encoders and faders on a device which only has a single set of faders, by assigning the shifted faders to the encoders, as shown above.
There are some additional directives (and corresponding command line options) to set midizap's Jack client name and the number of input and output ports it uses. (If both the command line options and directives in the midizaprc file are used, the former take priority, so that it's always possible to override the options in the midizaprc file from the command line.)
Firstly, there's the `-j` option and the `JACK_NAME` directive which change the Jack client name from the default (`midizap`) to whatever you want it to be. To use this option, simply invoke midizap as `midizap -j client-name`, or put the following directive into your midizaprc file:
This option is useful, in particular, if you're running multiple instances of midizap with different configurations for different controllers and/or target applications, and you want to have the corresponding Jack clients named appropriately, so that they can be identified more easily when wiring them up. If you're using a persistent MIDI patchbay, such as the one available in QjackCtl, you can then have the right connections automatically set up for you whenever you launch midizap with that specific configuration.
Secondly, we've already seen the `-o` option which is used to equip the Jack client with an additional output port. This can also be achieved with the `JACK_PORTS` directive in the midizaprc file, as follows:
You may want to place this directive directly into a configuration file if the configuration is primarily aimed at doing MIDI translations, so you'd like to have the MIDI output enabled by default. Typically, such configurations will include just a default `[MIDI]` section and little else. As explained below, it's also possible to have *two* pairs of input and output ports, in order to deal with controller feedback from the application. This is achieved by either invoking midizap with the `-o2` option, or by employing the `JACK_PORTS 2` directive in the configuration file.
Last but not least, midizap also supports Jack session management, which makes it possible to record the options the program was invoked with, along with all the MIDI connections. This feature can be used with any Jack session management software. Specifically, QjackCtl has its own built-in Jack session manager which is available in its Session dialog. To use this, launch midizap and any other Jack applications you want to have in the session, use QjackCtl to set up all the connections as needed, and then the "Save" (or "Save and Quit") option in the Session dialog to have the session recorded. Now, at any later time you can relaunch the same session with the "Load" (or "Recent") option in the same dialog.
Some MIDI controllers need a more elaborate setup than what we've seen so far, because they have motor faders, LEDs, etc. requiring feedback from the application. To accommodate these, you can use the `-o2` option of midizap, or the `JACK_PORTS 2` directive in the midizaprc file, to create a second pair of MIDI input and output ports, named `midi_input2` and `midi_output2`. Use of this option also activates a second MIDI default section in the midizaprc file, labeled `[MIDI2]`, which is used exclusively for translating MIDI from the second input port and sending the resulting MIDI data to the second output port. Typically, the translations in the `[MIDI2]` section will be the inverse of those in the `[MIDI]` section, or whatever it takes to translate the MIDI feedback from the application back to MIDI data which the controller understands.
You then wire up midizap's `midi_input` and `midi_output` ports to controller and application as before, but in addition you also connect the application back to midizap's `midi_input2` port, and the `midi_output2` port to the controller. This reverse path is what is needed to translate the feedback from the application and send it back to the controller. A full-blown example for this kind of setup can be found in examples/APCmini.midizaprc in the sources, which shows how to emulate a Mackie controller with AKAI's APCmini device, so that it readily works with DAW software such as Ardour and Reaper.
The names of some of the debugging options are rather peculiar. That's mainly due to historical reasons and my laziness; midizap inherited them from Eric Messick's ShuttlePRO program on which midizap is based (see below). So they'll probably last until someone comes up with some really good names.
midizap tries to keep things simple, which implies that it has its limitations. In particular, aftertouch and system messages are not supported right now, there's only one internal shift state, and midizap lacks some more interesting ways of mapping MIDI data. There are other, more powerful ways of doing these things, but they are also more complicated and usually require programming. So, while midizap often does the job reasonably well for simple mapping tasks, if things start getting fiddly then you're usually better off using a more comprehensive tool like [Pd][].
Eric Messick's [ShuttlePRO][nanosyzygy/ShuttlePRO] program, on which midizap is based, provides pretty much the same functionality for the Contour Design Shuttle devices.
This is a version of Eric Messick's ShuttlePRO program which has been redesigned to use Jack MIDI instead of the Contour Design Shuttle devices that the original program was written for.
[ShuttlePRO][nanosyzygy/ShuttlePRO] was written in 2013 by Eric Messick, based on earlier code by Trammell Hudson (<hudson@osresearch.net>) and Arendt David (<admin@prnet.org>). The present version of the program, written by Albert Graef, is based on his [fork][agraef/ShuttlePRO] of the program. All the translation features of Eric's version are still there (in particular, key and mouse translations work exactly the same), but of course the code has undergone some significant changes to accommodate the MIDI input and output facilities. The Jack MIDI driver code is based on code from Spencer Jackson's [osc2midi][] utility, and on the simple_session_client.c example available in the Jack [git repository][jackaudio/example-clients].
