What causes "[acestep-cpp] ERROR: failed to write %s\n" in mudler/LocalAI?

Check that the parent directory of dst exists and is writable (mkdir -p it before generating).

[acestep-cpp] ERROR: failed to write %s\n

Error message

[acestep-cpp] ERROR: failed to write %s\n

What it means

audio_write_wav() returned false when writing the normalized stereo PCM to the destination WAV path at 48 kHz. This is an I/O-level failure at the very last step (exit code 7): the generation itself succeeded, only persisting the file failed. Causes are typically an unwritable directory, a full disk, or a path encoding/permission problem.

Source

Thrown at backend/go/acestep-cpp/cpp/goacestepcpp.cpp:295

        int   n_samples = 2 * T_audio;
        for (int i = 0; i < n_samples; i++) {
            float a = audio[i] < 0 ? -audio[i] : audio[i];
            if (a > peak) {
                peak = a;
            }
        }
        if (peak > 1e-6f) {
            const float target_amp = powf(10.0f, -1.0f / 20.0f);
            float       gain       = target_amp / peak;
            for (int i = 0; i < n_samples; i++) {
                audio[i] *= gain;
            }
        }
    }

    // 13. Write WAV output
    if (!audio_write_wav(dst, audio.data(), T_audio, 48000)) {
        fprintf(stderr, "[acestep-cpp] ERROR: failed to write %s\n", dst);
        return 7;
    }

    fprintf(stderr, "[acestep-cpp] Wrote %s: %d samples (%.2fs @ 48kHz stereo)\n",
            dst, T_audio, (float)T_audio / 48000.0f);
    return 0;
}

View on GitHub (pinned to 44413a9d06)

Solutions

Check that the parent directory of dst exists and is writable (mkdir -p it before generating).
Verify free disk space — the WAV is uncompressed stereo PCM at 48 kHz.
Run the write path manually (touch the exact dst) to surface permission errors, and inspect errno-level messages on stderr.
If running in a container, confirm the output volume is mounted read-write.

Example fix

// before
snprintf(dst, sizeof dst, "/tmp/out/%s.wav", name);
// after: ensure the directory exists before generating
mkdir("/tmp/out", 0755);
snprintf(dst, sizeof dst, "/tmp/out/%s.wav", name);

Defensive patterns

Strategy: validation

Validate before calling

if dir := filepath.Dir(dst); dir != "" {
    if err := os.MkdirAll(dir, 0o755); err != nil {
        return fmt.Errorf("output dir: %w", err)
    }
}
if err := unix.Access(dir, unix.W_OK); err != nil {
    return fmt.Errorf("output dir not writable: %w", err)
}

Prevention

Create and probe-writable the output directory before an expensive generation run.
Check free disk space proportional to duration (48 kHz stereo PCM ≈ 384 KB/s).
Surface the dst path in errors so users see which path failed.

When it happens

Trigger: Calling generate with a dst path whose parent directory does not exist or is not writable, a read-only filesystem or container mount, or disk exhaustion (48 kHz stereo floats are heavy — minutes of audio are tens of MB).

Common situations: Output dir not created before the call in a scratch/container environment; running under a user without write permission to the model/output folder; disk-full after large model downloads consumed space; dst containing characters the platform rejects.

Related errors

AI-assisted analysis of mudler/LocalAI@44413a9d06 (2026-08-15). Data as JSON: /api/errors/9be70e1a95bd435d. Report an issue: GitHub.