Channels issues break the app

[danialt]

Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

So far love the Alphatabs! there is an issue that has blocked me for days, could you help maybe?

I am importing guitar pro files, and for some of them, I receive the following error:

alphatab.js:26549 Uncaught TypeError: Cannot read properties of undefined (reading 'midiVolume')
    at TinySoundFont.channelMidiControl (alphatab.js:26549:69)
    at TinySoundFont.processMidiMessage (alphatab.js:25920:26)
    at TinySoundFont.fillWorkingBuffer (alphatab.js:25879:26)
    at TinySoundFont.synthesize (alphatab.js:25770:25)
    at alphatab.js:27225:69
    at EventEmitter.trigger (alphatab.js:27032:17)
    at AlphaSynthWorkerSynthOutput.handleMessage (alphatab.js:27549:40)

As my last resort I may start patching the original file around variable ´c´ but thought maybe there is a better way?

My app is a NextJS react app.

Expected Behavior

Some guitar pro files have this issue, but since I am not familiar with the internals I can only guess channel information is missing?

Steps To Reproduce

Link to jsFiddle, CodePen, Project

No response

Found in Version

1.4 (alpha)

Platform

Web

Environment

- **OS**: MacOS
- **Browser**: Chrome
- **.net Version**:

Anything else?

No response

[Danielku15]

can you provide a full reproducible example? (e.g. on stackblitz) without the input files and seeing some code, its hard to reproduce whats going on here. 😉

[Danielku15]

Ping @danialt
Without further info I cannot look deeper and I'll have to close this bug report

[danialt]

hi @Danielku15,

here's the guitar pro tab:

marooned.gp.zip

it gives this error upon initialization:

alphaTab.core.mjs?v=f66d9966:25781 Uncaught TypeError: Cannot set properties of undefined (setting 'mixVolume')
    at TinySoundFont.channelSetMixVolume (alphaTab.core.mjs?v=f66d9966:25781:21)
    at AlphaSynth.setChannelVolume (alphaTab.core.mjs?v=f66d9966:27396:27)
    at AlphaSynthWebWorker.handleMessage (alphaTab.core.mjs?v=f66d9966:27689:30

I was working on it even today when I found a bit free time but still stuck, would appreciate if you could check. I patched the main file of alphatab where everywhere c was called to check if it exists before asking for properties, but maybe there is a better way.

My stack: React + Vite

uploading it shortly...

[danialt]

here's the demo: https://firetabsv2.vercel.app/debug.html and thank you in advance for this amazing library 🎖

Just for the sake of curiosity and lack of internal knowledge of alphatabs, I fed the code to gemini and got the following:

Okay, I see the errors you're encountering with `alphaTab.core.mjs`. Let's break down what's happening.

**Error Analysis:**

All the errors you've listed (`TypeError: Cannot set properties of undefined (setting 'mixVolume')`, `TypeError: Cannot read properties of undefined (reading 'midiVolume')`, etc.) point to the same fundamental problem: the code is trying to access or modify a property on an object that is `undefined`.

Looking at the specific lines mentioned in the stack traces:

1.  **`TinySoundFont.channelSetMixVolume` (line 25781):**
    ```javascript
    25780 |         if (channel >= 0 && channel < this.channels.length) {
    25781 |             this.channels[channel].mixVolume = volume; // Error here
    25782 |         }
    ```
    The error occurs because `this.channels[channel]` evaluates to `undefined`.

2.  **`TinySoundFont.channelMidiControl` (lines 26538, 26548, 26558, 26589):**
    ```javascript
    26535 |         if (channel >= 0 && channel < this.channels.length) {
    26536 |             let c = this.channels[channel]; // c becomes undefined
    26537 |             switch (control) {
    26538 |                 case 7: c.midiVolume = value; break; // Error here
    // ... other cases accessing properties of c ...
    26548 |                 case 11: c.midiExpression = value; break; // Error here
    // ...
    26558 |                     c.midiPan = value; // Error here
    // ...
    26589 |                 } // Error likely occurs within logic involving c.midiRpn or related properties accessed later in the function
    // ...
    ```
    Similarly, the errors happen because `c`, which is assigned `this.channels[channel]`, is `undefined`.

**Root Cause Hypothesis:**

The `TinySoundFont` class uses an array called `channels` to store the state for each MIDI channel (volume, pan, pitch bend, etc.). The errors indicate that for the specific `channel` number being processed at the time of the error, the corresponding entry in the `this.channels` array is `undefined`.

This could happen for a few reasons:

1.  **Channel Initialization:** The `channels` array might not be getting fully initialized with `Channel` objects for all required channels (typically 0-16) when the `TinySoundFont` instance is created or reset.
2.  **Invalid Channel Access:** Although there are checks like `channel >= 0 && channel < this.channels.length`, it's possible that under certain conditions (perhaps related to timing or specific MIDI sequences), an invalid channel number is used, or the `channels` array itself is in an unexpected state (e.g., `null` or having `undefined` entries).
3.  **Asynchronous State Issues:** The involvement of `AlphaSynthWebWorker` suggests asynchronous operations. There might be a race condition where channel properties are accessed before the channel state is fully set up or after it has been prematurely cleared during a reset operation (`channelReset`, `resetSoft`, `noteOffAll`).

**Conclusion:**

The core issue is that the synthesizer is attempting to operate on a MIDI channel that hasn't been properly initialized or whose state has become invalid (`undefined`) within the `TinySoundFont`'s internal `channels` array. This points towards a potential bug in alphaTab's channel management or initialization logic, possibly related to how it handles MIDI events or resets within the Web Worker context.

To fix this, one would typically need to debug the alphaTab library code to ensure:
*   The `channels` array in `TinySoundFont` is always correctly initialized with the expected number of `Channel` objects.
*   Channel state is properly managed during resets and asynchronous operations.
*   Valid channel numbers are consistently used throughout the relevant functions.
´´´

[Danielku15]

@danialt Was this guitar pro file really written by Guitar Pro 8? It has some suspicious indicators that a 3rd party software might have written this file. There are indentions and line breaks in the score.gpif file which I haven't seen before. Additionally some values which are always filled by Guitar Pro (and causing this issue) are not filled in this file.

Maybe these files you are testing originate from some other software or platform which has generated them?

I could add some workarounds for the currently known issues, but it would be good to narrow down the root cause.