Media Midi

Media MIDI

Context: $ARGUMENTS

Wire-level MIDI 1.0 + 2.0, Standard MIDI Files (SMF), and control-surface plumbing. Not a DAW — for sequencing use a DAW; this skill is the CLI layer under it.

Quick start

• List MIDI ports: → Step 1 (list-ports)
• Send a note-on to port X: → Step 2 (send note-on --port "IAC" --channel 1 --note 60 --velocity 100)
• Monitor incoming MIDI: → Step 3 (dump)
• Parse a .mid file: → Step 4 (smf-dump file.mid)
• Author a .mid programmatically: → Step 4 (smf-write --json events.json --out song.mid)

When to use

• Trigger notes / CCs / program changes from a shell script (automation, QA, live show cues).
• Build a control surface that speaks to Ableton / Logic / Pro Tools / Reaper / MainStage / Bitwig.
• Round-trip parse and author .mid files programmatically (Standard MIDI File format 0/1/2).
• Sniff a hardware controller's output for reverse-engineering.
• Work with MIDI 2.0 UMP packets (32/64/96/128-bit) when the target supports it.

Step 1 — Detect ports

midictl.py list-ports probes the platform and shells out to the appropriate tool:

• macOS: sendmidi list (if installed) or uses Core MIDI directly via mido/rtmidi if present.
• Linux: amidi -l + aconnect -l (ALSA).
• Windows: sendmidi list.

uv run ${CLAUDE_SKILL_DIR}/scripts/midictl.py list-ports

Install tools (macOS/Linux/Windows cross-platform): brew install gbevin/tools/sendmidi (also installs receivemidi).

Step 2 — Send messages

# Note on/off at channel 1 (1-indexed in CLI, 0x90/0x80 on wire)
uv run ${CLAUDE_SKILL_DIR}/scripts/midictl.py send note-on \
    --port "IAC Driver Bus 1" --channel 1 --note 60 --velocity 100
uv run ${CLAUDE_SKILL_DIR}/scripts/midictl.py send note-off \
    --port "IAC Driver Bus 1" --channel 1 --note 60

# Continuous controller
uv run ${CLAUDE_SKILL_DIR}/scripts/midictl.py send cc \
    --port "IAC Driver Bus 1" --channel 1 --cc 74 --value 64

# Program change
uv run ${CLAUDE_SKILL_DIR}/scripts/midictl.py send program \
    --port "IAC Driver Bus 1" --channel 1 --program 42

# System Exclusive
uv run ${CLAUDE_SKILL_DIR}/scripts/midictl.py send sysex \
    --port "IAC Driver Bus 1" --hex 'F0 7E 7F 06 01 F7'  # Identity request

Step 3 — Monitor

uv run ${CLAUDE_SKILL_DIR}/scripts/midictl.py dump --port "MyController"
# or on Linux specifically via aseqdump
uv run ${CLAUDE_SKILL_DIR}/scripts/midictl.py monitor --port 24:0

Step 4 — SMF files

# Parse .mid to human-readable events + JSON
uv run ${CLAUDE_SKILL_DIR}/scripts/midictl.py smf-dump song.mid --format json

# Author .mid from a JSON event list
uv run ${CLAUDE_SKILL_DIR}/scripts/midictl.py smf-write \
    --json events.json --out song.mid --ppq 480 --format 1

Input JSON schema (each entry = {delta_ticks, type, channel, data1, data2, [meta: name, tempo, time_sig, ...]}).

Gotchas

• MIDI 1.0 serial is 31,250 bps 8-N-1. USB-MIDI and BLE-MIDI wrap the same status+data bytes in USB-MIDI Class (CIN codes) or BLE-MIDI (timestamp headers). The message semantics are identical.
• Status byte high bit is set (0x80-0xFF). Data bytes are 7-bit (MSB clear). If a data byte has its MSB set, your stream is broken.
• Running status is legal and common. Subsequent Channel Voice messages of the same status may omit the status byte. Parsers that don't track running status will lose data.
• Sysex is F0 <manufacturer> ... F7. Never truncate before F7 — dropped F7 hangs the device. Universal Real-Time / Non-Real-Time sysex use mfr IDs 7E/7F.
• MIDI 2.0 UMP ≠ MIDI 1.0. UMP is 32/64/96/128-bit packets; 16 "groups" × 16 channels. Messages Type 0x2 (MIDI 1.0 CV in UMP) ≠ Type 0x4 (MIDI 2.0 CV). MIDI-CI discovery/negotiation runs over MIDI 1.0 sysex, not over UMP.
• SMF = MThd (6 B: format, ntracks, division) + MTrk chunks. Each MTrk event is VLQ delta-time + event stream. Format 0 = one track, Format 1 = multiple tracks sharing tempo map, Format 2 = independent tracks (rare).
• VLQ (variable-length quantity) is big-endian base-128. Each byte's high bit signals continuation (1 = more bytes, 0 = last). 0x40 = 64, 0x81 0x00 = 128, 0x82 0x80 0x00 = 32768. Get this wrong and your whole SMF is misaligned.
• Tempo meta-event is microseconds per quarter note (500000 = 120 BPM), not BPM directly.
• Channels are 1-indexed in UIs but 0-indexed on the wire. Ch 1 = status nibble 0. The helper takes 1-indexed --channel values.
• rtmidi-cli does NOT exist as a packaged binary. Don't reference it. The Python python-rtmidi library is real; sendmidi/receivemidi by gbevin are the real cross-platform CLIs.
• Full MIDI 2.0 spec PDFs are login-gated at https://midi.org/join-now. Public overviews live at https://midi.org/specs. Link both; note the gate.
• BLE-MIDI timestamp overflow at 13 bits = 8192 ms. Long sysex must be split into multiple BLE packets with timestamp continuation bytes.
• ALSA sequencer addresses look like client:port (e.g. 128:0), not device paths. Use aconnect -l to enumerate.
• On macOS, the IAC Driver is off by default. Enable it in Audio MIDI Setup → MIDI Studio → IAC Driver → check "Device is online" — otherwise there are no virtual ports to send to.

Examples

Example 1 — Trigger a C-major chord

for n in 60 64 67; do
    uv run ${CLAUDE_SKILL_DIR}/scripts/midictl.py send note-on \
        --port "IAC Driver Bus 1" --channel 1 --note $n --velocity 100
done
sleep 1
for n in 60 64 67; do
    uv run ${CLAUDE_SKILL_DIR}/scripts/midictl.py send note-off \
        --port "IAC Driver Bus 1" --channel 1 --note $n
done

Example 2 — Identity request (universal sysex)

uv run ${CLAUDE_SKILL_DIR}/scripts/midictl.py send sysex \
    --port "MyController" --hex 'F0 7E 7F 06 01 F7'

Example 3 — Dump events from a .mid

uv run ${CLAUDE_SKILL_DIR}/scripts/midictl.py smf-dump song.mid

Example 4 — Build a tiny SMF

cat > events.json <<'JSON'
[
  {"delta": 0, "type": "tempo", "bpm": 120},
  {"delta": 0, "type": "note-on", "channel": 1, "note": 60, "velocity": 100},
  {"delta": 480, "type": "note-off", "channel": 1, "note": 60}
]
JSON
uv run ${CLAUDE_SKILL_DIR}/scripts/midictl.py smf-write --json events.json --out c.mid

Reference docs

• references/cc-table.md — complete MIDI 1.0 CC number table (0-127) with official names.
• references/ump-packets.md — MIDI 2.0 UMP type/status codes.

Troubleshooting

port "X" not found

Cause: Port name typo, IAC disabled (macOS), or ALSA sequencer subsystem not loaded. Solution: Run list-ports to see the canonical names. On macOS enable IAC in Audio MIDI Setup. On Linux ensure snd-seq module is loaded.

Notes hang (never stop)

Cause: Missed note-off. Happens with aborted scripts. Solution: Send CC 123 (All Notes Off) to the channel or power-cycle the synth.

sendmidi not found

Cause: Not installed. Solution: brew install gbevin/tools/sendmidi. Helper falls back to ALSA amidi / Python mido/rtmidi if any is available.

Parser errors on SMF

Cause: Malformed VLQ or missing F7 terminator in an embedded sysex. Solution: Inspect the file with od -c or xxd; compare against spec in references/.