使用 Obj-C 插件和 AVAssetWriterInput 向视频添加音频

Posted 2023-02-25

【中文标题】使用 Obj-C 插件和 AVAssetWriterInput 向视频添加音频

【英文标题】：Adding audio to a video using Obj-C plugin and AVAssetWriterInput

【发布时间】：2012-10-17 18:28:24

【问题描述】：

我正在尝试拍摄使用 iVidCap 插件创建的视频并向其添加音频。基本上与这个问题完全相同：Writing video + generated audio to AVAssetWriterInput, audio stuttering。我使用这篇文章中的代码作为基础尝试自己修改 iVidCap.mm 文件，但应用程序总是在 endRecordingSession 中崩溃。

我不确定我需要如何修改 endRecordingSession 以适应音频（原始插件只是创建一个视频文件）。这是函数：

- (int) endRecordingSession: (VideoDisposition) action 

NSLog(@"Start endRecordingSession");
NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];

NSLog(@"Auto released pool");

NSString *filePath;
BOOL success = false;

[videoWriterInput markAsFinished];
NSLog(@"Mark video writer input as finished");
//[audioWriterInput markAsFinished];

// Wait for the video status to become known.
// Is this really doing anything?
int status = videoWriter.status;
while (status == AVAssetWriterStatusUnknown) 
    NSLog(@"Waiting for video to complete...");
    [NSThread sleepForTimeInterval:0.5f];
    status = videoWriter.status;


NSLog(@"Video completed");

@synchronized(self) 
    success = [videoWriter finishWriting];
    NSLog(@"Success: %@", success);
    if (!success) 
        // We failed to successfully finalize the video file.
        NSLog(@"finishWriting returned NO");

     else 
        // The video file was successfully written to the Documents folder.
        filePath = [[self getDocumentsFileURL:videoFileName] path];
        if (action == Save_Video_To_Album) 

            // Move the video to an accessible location on the device.
            NSLog(@"Temporary video filePath=%@", filePath);
            if (UIVideoAtPathIsCompatibleWithSavedPhotosAlbum(filePath)) 
                NSLog(@"Video IS compatible. Adding it to photo album.");
                UISaveVideoAtPathToSavedPhotosAlbum(filePath, self, @selector(copyToPhotoAlbumCompleteFromVideo: didFinishSavingWithError: contextInfo:), nil);
             else 
                NSLog(@"Video IS NOT compatible. Could not be added to the photo album.");
                success = NO;
            
         else if (action == Discard_Video) 
            NSLog(@"Video cancelled. Removing temporary video file: %@", filePath);
            [self removeFile:filePath];  
        
    

    [self cleanupWriter];


isRecording = false;

[pool drain];

return success; 

现在它在 [videoWriter finishWriting] 上崩溃。我尝试添加 [audioWriterInput markAsFinished]，但随后它崩溃了。我会联系原始发帖者，因为他们似乎可以正常工作，但似乎没有办法发送私人消息。

是否有人对我如何使其工作或为什么会崩溃有任何建议？我已经尽力解决这个问题，但我对 Obj-C 还是很陌生。如果需要，我可以发布其余代码（其中很多都在前面引用的原始帖子中）。

【参考方案1】：

问题实际上可能出在 writeAudioBuffer 函数中。

如果你从那篇文章中复制了代码但没有更改它，那么你肯定会遇到一些问题。

你需要做这样的事情：

if ( ![self waitForAudioWriterReadiness]) 
    NSLog(@"WARNING: writeAudioBuffer dropped frame after wait limit reached.");
    return 0;


OSStatus status;
CMBlockBufferRef bbuf = NULL;
CMSampleBufferRef sbuf = NULL;

size_t buflen = n * nchans * sizeof(float);

CMBlockBufferRef tmp_bbuf = NULL;
status = CMBlockBufferCreateWithMemoryBlock(
                                            kCFAllocatorDefault, 
                                            samples, 
                                            buflen, 
                                            kCFAllocatorDefault, 
                                            NULL, 
                                            0, 
                                            buflen, 
                                            0, 
                                            &tmp_bbuf);

if (status != noErr || !tmp_bbuf) 
    NSLog(@"CMBlockBufferCreateWithMemoryBlock error");
    return -1;

// Copy the buffer so that we get a copy of the samples in memory.
// CMBlockBufferCreateWithMemoryBlock does not actually copy the data!
// 
status = CMBlockBufferCreateContiguous(kCFAllocatorDefault, tmp_bbuf, kCFAllocatorDefault, NULL, 0, buflen, kCMBlockBufferAlwaysCopyDataFlag, &bbuf);
//CFRelease(tmp_bbuf); // causes abort?!
if (status != noErr) 
    NSLog(@"CMBlockBufferCreateContiguous error");
    //CFRelease(bbuf);
    return -1;



CMTime timestamp = CMTimeMake(sample_position_, 44100);

status = CMAudiosampleBufferCreateWithPacketDescriptions(
    kCFAllocatorDefault, bbuf, TRUE, 0, NULL, audio_fmt_desc_, 1, timestamp, NULL, &sbuf);

sample_position_ += n;
if (status != noErr) 
    NSLog(@"CMSampleBufferCreate error");
    return -1;

BOOL r = [audioWriterInput appendSampleBuffer:sbuf];
if (!r) 
    NSLog(@"appendSampleBuffer error");

//CFRelease(bbuf); // crashes, don't know why..  Is there a leak here?
//CFRelease(sbuf);

return 0;

我在这里不确定与内存管理有关的一些事情。

另外一定要使用：

audioWriterInput.expectsMediaDataInRealTime = YES;