Load from bytes

You already have the bytes — from a fetch with auth headers, a <input type="file"> upload, an IndexedDB cache, or a Node.js readFile on the server. Hand the buffer to api.load() and skip the built-in fetcher entirely.

Fetching bytes…

When the bytes come from you

Any pipeline that already has the file in memory belongs here:

• Node.js and server-side rendering — fs.readFileSync produces a Buffer.
• Backends that stream from S3, a database blob column, or an internal API.
• Browser code that fetched the file with a custom fetch (auth headers, retries, progress reporting).
• Desktop and mobile hosts that read from the local filesystem or a content provider.

api.load() accepts a Uint8Array or an ArrayBuffer on every runtime. alphaTab probes the leading bytes to pick an importer — Guitar Pro, MusicXML, Capella, or alphaTex — so you do not tell it what format you handed over.

Pair it with track selection

The second argument to api.load() picks which tracks render on arrival. Pass [0] to open a multi-track file on the first track only, or [0, 2, 5] to render a subset. Omitting the argument uses whatever core.tracks was set to at construction time.

Show it in code

import * as alphaTab from '@coderline/alphatab';

const container = getAlphaTabContainer();
const api = new alphaTab.AlphaTabApi(container, {
  // No core.file here — the bytes arrive after construction.
});

const bytes = await readScoreFile('song.gp');
api.load(bytes, [0]);

api.scoreLoaded.on((score) => {
  console.log(`Loaded ${score.title}, ${score.tracks.length} tracks total`);
});

getAlphaTabContainer() is a placeholder for the platform-specific step of obtaining the render target. readScoreFile() is a placeholder for the platform-specific step of producing a Uint8Array — fs.promises.readFile on Node.js, System.IO.File.ReadAllBytes on .NET, ContentResolver.openInputStream on Android, or fetch(...).then(r => r.arrayBuffer()) in the browser.

Where to look next

• Load from a URL — the browser-only path when alphaTab does the fetch.
• Direct importer use — build a Score from bytes without instantiating an API.
• Reacting to a loaded score — the scoreLoaded event.
• Selecting and switching tracks — the second argument to api.load().
• api.load and core.tracks in the reference.