How to simplify this code? Promises won't help, as leaving the stack causes the IndexedDB transactions to close.

gistfile1.txt

    function remix(recording, frameSwitches) {

        var keyRanges = [];

        var lastRecordingId = null;
        var lastTimeRange = Number.MIN_VALUE;

        frameSwitches.switches.forEach(function(frameSwitch) {

            if (lastRecordingId !== null) {
                var boundStart = [lastRecordingId, lastTimeRange];
                var boundEnd = [lastRecordingId, frameSwitch.time];
                keyRanges.push(IDBKeyRange.bound(boundStart, boundEnd, false, true));
            }

            lastRecordingId = frameSwitch.recordingId;
            lastTimeRange = frameSwitch.time;
        });

        keyRanges.push(IDBKeyRange.bound([lastRecordingId, lastTimeRange], [lastRecordingId, Number.MAX_VALUE], false, true));

        return openDatabase()
        .then(function(db) {

            var transaction = db.transaction([recordingStoreName, framesStoreName], "readwrite");
            var deferred = deferredWatchingOnerror(transaction);

            var request = transaction.objectStore(recordingStoreName).put(recording);

            request.onsuccess = pumpNextKeyRange;

            function pumpNextKeyRange() {

                if (keyRanges.length === 0) {
                    deferred.resolve();
                    return;
                }

                var nextKeyRange = keyRanges.shift();

                var readRequest = transaction.objectStore(framesStoreName).index("byRecordingAndTime").openCursor(nextKeyRange);

                readRequest.onsuccess = function(event) {

                    var cursor = event.target.result;

                    if (!cursor) {
                        pumpNextKeyRange();
                    } else {
                        var entry = cursor.value;

                        entry.recordingId = recording.id;

                        var writeRequest = transaction.objectStore(framesStoreName).put(entry);

                        writeRequest.onsuccess = function() {
                            cursor.continue();
                        };
                    }
                };
            }

            return deferred.promise.finally(function() {
                db.close();
            });            
        });
    }