Add support for MIDI controller targets and clip envelopes in Ableton export

src/lib/exporters/ableton/midi.ts

@@ -0,0 +1,83 @@
+import type { AblMidiEvent } from '../../transformers/ableton';
+
+export type AbletonMidiControllerTargets = Record<string, { '@Id': number }>;
+
+type AutomationPoint = {
+  time: number;
+  value: number;
+};
+
+const CHANNEL_PRESSURE_TARGET = 129;
+const SENTINEL_TIME = -63072000;
+
+export function decodeChannelPressure(event: AblMidiEvent) {
+  if (
+    event.data.length !== 4 ||
+    event.data[0] !== 0xd0 ||
+    event.data[1] > 127 ||
+    event.data[2] !== 0xff ||
+    event.data[3] !== 0
+  ) {
+    return undefined;
+  }
+
+  return event.data[1];
+}
+
+function floatEvents(points: AutomationPoint[]) {
+  return points.map((point, index) => ({
+    '@Id': index,
+    '@Time': point.time,
+    '@Value': point.value,
+  }));
+}
+
+export function buildMidiClipEnvelopes(
+  events: AblMidiEvent[],
+  controllerTargets: AbletonMidiControllerTargets,
+) {
+  const target = controllerTargets[`ControllerTargets.${CHANNEL_PRESSURE_TARGET}`]?.['@Id'];
+  if (target === undefined) {
+    return [];
+  }
+
+  const points: AutomationPoint[] = [{ time: SENTINEL_TIME, value: 0 }];
+  let previousValue = 0;
+  let eventCount = 0;
+
+  events.forEach((event) => {
+    const value = decodeChannelPressure(event);
+    if (value === undefined) {
+      return;
+    }
+
+    const time = event.position / 96;
+    points.push({ time, value: previousValue });
+    points.push({ time, value });
+    previousValue = value;
+    eventCount++;
+  });
+
+  if (eventCount === 0) {
+    return [];
+  }
+
+  return [
+    {
+      '@Id': 0,
+      EnvelopeTarget: { PointeeId: { '@Value': target } },
+      Automation: {
+        Events: { FloatEvent: floatEvents(points) },
+        AutomationTransformViewState: {
+          IsTransformPending: { '@Value': 'false' },
+          TimeAndValueTransforms: {},
+        },
+      },
+      LoopSlot: { Value: {} },
+      ScrollerTimePreserver: {
+        LeftTime: { '@Value': 0 },
+        RightTime: { '@Value': 0 },
+      },
+    },
+  ];
+}