Android平台FMOD v1.10低阶API保存带DSP效果文件过慢排查求助

Alright, let's break down your two FMOD issues on Android step by step. I’ve worked with FMOD’s low-level API extensively for audio processing, so here’s what’s going wrong and how to fix it.

1. Zero-Size File When Using FMOD_OUTPUTTYPE_WAVWRITER_NRT #

Looking at your code snippet, there are two critical mistakes causing the 0-byte file problem:

Wrong Output Type Enumeration #

Your code calls system->setOutput(FMOD_OUTPUTTYPE_WAVWRITER), but you’re trying to use the Non-Real-Time (NRT) writer. These are distinct output types—FMOD_OUTPUTTYPE_WAVWRITER is real-time (tied to audio playback speed), while FMOD_OUTPUTTYPE_WAVWRITER_NRT is designed for offline, fast processing. You need to specify the correct enum value.

Missing Critical Cleanup & Loop Logic #

NRT mode doesn’t write the full file (including essential header data like sample rate/channels) until you properly release the FMOD system. If your loop exits early or you skip system->release(), the file will remain empty. Here’s the corrected workflow:

// Step 1: Set NRT output type
FMOD_RESULT result = system->setOutput(FMOD_OUTPUTTYPE_WAVWRITER_NRT);
ERRCHECK(result);

// Step 2: Initialize system with output path
result = system->init(16, FMOD_INIT_NORMAL, (void *)outpath);
ERRCHECK(result);

// Step 3: Load and play your audio (fill in your existing sound/channel setup)
FMOD::Sound* sound = nullptr;
result = system->createSound("your_source_audio.mp3", FMOD_DEFAULT, nullptr, &sound);
ERRCHECK(result);

FMOD::Channel* channel = nullptr;
result = system->playSound(sound, nullptr, false, &channel);
ERRCHECK(result);

// Step 4: NRT update loop - run until audio finishes
bool isPlaying = true;
while (isPlaying) {
    // Process audio data in NRT mode
    result = system->update();
    ERRCHECK(result);

    // Check if playback has completed
    result = channel->isPlaying(&isPlaying);
    if (result != FMOD_OK) {
        isPlaying = false;
    }
}

// Step 5: Critical! Release resources to finalize the file
sound->release();
system->release();

Key note: NRT mode buffers audio data during update() calls, but the file header and final data flush only happen when you call system->release(). Skip this step, and you’ll get a 0-byte file every time.

2. Saving 20-Second Audio Takes Longer Than 20 Seconds #

This slowdown typically stems from one of these issues:

Real-Time Writer Limitation #

If you’re using FMOD_OUTPUTTYPE_WAVWRITER (real-time mode), FMOD writes data at the actual playback speed—so a 20-second file will take at least 20 seconds to save. Switch to FMOD_OUTPUTTYPE_WAVWRITER_NRT (as fixed above) to process and write audio as fast as your device’s CPU/IO allows, which should cut down saving time significantly.

Android Storage IO Bottlenecks #

External storage (SD cards) on Android is often slower than internal app storage. Try saving the file to your app’s private directory (e.g., getFilesDir() in Java/Kotlin, or equivalent in C++) to rule out slow external storage as the culprit.

MP3 Encoding Overhead #

MP3 is a compressed format, and FMOD’s MP3 encoder uses CPU resources that can slow down saving on lower-end Android devices. Test saving as a WAV file first—WAV is uncompressed, so it writes much faster. If WAV saves quickly, the delay is likely from MP3 encoding.

Unnecessary FMOD Features #

If you’ve enabled 3D audio, DSP effects, or other non-essential features in your FMOD_INIT_* flags, these add processing overhead. Stick to FMOD_INIT_NORMAL or try FMOD_INIT_STREAM_FROM_UPDATE for leaner offline processing.

Extra Troubleshooting Tips #

• Check Permissions: On Android 6.0+, ensure your app has the WRITE_EXTERNAL_STORAGE permission (or MANAGE_EXTERNAL_STORAGE for Android 10+ if writing to public directories). Missing permissions can cause silent failures or slow writes.
• Enable FMOD Logs: Add system->setLogLevel(FMOD_LOG_LEVEL_DEBUG) to get detailed logs. Look for errors related to file IO or audio processing—this will help pinpoint hidden issues.

内容的提问来源于stack exchange，提问作者fm927