EthFiddle - Solidity IDE in the Browser. Powered By Loom Network

pragma solidity ^0.7.1;

contract MidiContract {
    struct NoteEvent {
        bytes pitch;
        uint8 duration;
    }

struct Track {
        NoteEvent[] events;
    }

function generateMidiFile() public pure returns (string memory) {
        Track[] memory tracks = new Track[](1);

Track memory track = Track({
            events: [
                NoteEvent({
                    pitch: hex"45 34",
                    duration: 4
                }),
                NoteEvent({
                    pitch: hex"43",
                    duration: 2
                }),
                NoteEvent({
                    pitch: hex"45 34",
                    duration: 4
                }),
                NoteEvent({
                    pitch: hex"43",
                    duration: 2
                }),
                NoteEvent({
                    pitch: hex"43 43 43 43 44 44 44 44",
                    duration: 8
                }),
                NoteEvent({
                    pitch: hex"45 34",
                    duration: 4
                }),
                NoteEvent({
                    pitch: hex"43",
                    duration: 2
                })
            ]
        });

tracks[0] = track;

string memory midiData = "";

for (uint i = 0; i < tracks.length; i++) {
            Track memory t = tracks[i];
            string memory trackData = "";

for (uint j = 0; j < t.events.length; j++) {
                NoteEvent memory e = t.events[j];
                string memory noteData = string(abi.encodePacked(
                    "pitch:", e.pitch, ";",
                    "duration:", e.duration, ";"
                ));

trackData = string(abi.encodePacked(trackData, noteData));
            }

midiData = string(abi.encodePacked(midiData, trackData));
        }

return string(abi.encodePacked("data:audio/midi;base64,", Base64.encode(midiData)));
    }
}

library Base64 {
    bytes constant private TABLE = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

function encode(bytes memory data) internal pure returns (string memory) {
        uint256 len = data.length;
        if (len == 0) return "";

uint256 encodedLen = 4 * ((len + 2) / 3);

bytes memory result = new bytes(encodedLen);

uint256 j = 0;
        for (uint256 i = 0; i < len; i += 3) {
            uint256 octets = (uint256(data[i]) << 16) | (i + 1 < len ? uint256(data[i + 1]) << 8 : 0) | (i + 2 < len ? uint256(data[i + 2]) : 0);

result[j++] = TABLE[uint8(octets >> 18)];
            result[j++] = TABLE[uint8((octets >> 12) & 0x3f)];
            result[j++] = TABLE[uint8((octets >> 6) & 0x3f)];
            result[j++] = TABLE[uint8(octets & 0x3f)];
        }

if (len % 3 == 1) {
            result[encodedLen - 2] = '=';
            result[encodedLen - 1] = '=';
        } else if (len % 3 == 2) {
            result[encodedLen - 1] = '=';
        }

return string(result);
    }
}