ios - 使用 AVFoundation 将 AAC 音频和 h.264 视频流混合到 mp4
<p><p>对于 OSX 和 IOS,我有实时编码的视频 (h.264) 和音频 (AAC) 数据流传入,我希望能够将它们混合到一个 mp4 中。</p>
<p>我正在使用 <code>AVAssetWriter</code> 来执行复用。</p>
<p>我的视频可以正常工作,但我的音频听起来仍然像杂乱无章的静态声音。这是我现在正在尝试的(为简洁起见,这里跳过了一些错误检查):</p>
<p>我初始化编写器:</p>
<pre><code> NSURL *url = ;
NSError* err = nil;
mContext->writer = ;
</code></pre>
<p>我初始化音频输入:</p>
<pre><code> NSDictionary* settings;
AudioChannelLayout acl;
bzero(&acl, sizeof(acl));
acl.mChannelLayoutTag = kAudioChannelLayoutTag_Stereo;
settings = nil; // set output to nil so it becomes a pass-through
CMAudioFormatDescriptionRef audioFormatDesc = nil;
{
AudioStreamBasicDescription absd = {0};
absd.mSampleRate = mParameters.audioSampleRate; //known sample rate
absd.mFormatID = kAudioFormatMPEG4AAC;
absd.mFormatFlags = kMPEG4Object_AAC_Main;
CMAudioFormatDescriptionCreate(NULL, &absd, 0, NULL, 0, NULL, NULL, &audioFormatDesc);
}
mContext->aacWriterInput = ;
mContext->aacWriterInput.expectsMediaDataInRealTime = YES;
;
</code></pre>
<p>然后启动编写器:</p>
<pre><code> ;
;
</code></pre>
<p>然后,我有一个回调,我收到一个带有时间戳(毫秒)的数据包,以及一个包含 1024 个压缩样本的数据的 <code>std::vector<uint8_t></code>。我确保 <code>isReadyForMoreMediaData</code> 为真。然后,如果这是我们第一次收到回调,我设置了 CMAudioFormatDescription:</p>
<pre><code> OSStatus error = 0;
AudioStreamBasicDescription streamDesc = {0};
streamDesc.mSampleRate = mParameters.audioSampleRate;
streamDesc.mFormatID = kAudioFormatMPEG4AAC;
streamDesc.mFormatFlags = kMPEG4Object_AAC_Main;
streamDesc.mChannelsPerFrame = 2;// always stereo for us
streamDesc.mBitsPerChannel = 0;
streamDesc.mBytesPerFrame = 0;
streamDesc.mFramesPerPacket = 1024; // Our AAC packets contain 1024 samples per frame
streamDesc.mBytesPerPacket = 0;
streamDesc.mReserved = 0;
AudioChannelLayout acl;
bzero(&acl, sizeof(acl));
acl.mChannelLayoutTag = kAudioChannelLayoutTag_Stereo;
error = CMAudioFormatDescriptionCreate(kCFAllocatorDefault, &streamDesc, sizeof(acl), &acl, 0, NULL, NULL, &mContext->audioFormat);
</code></pre>
<p>最后,我创建了一个 <code>CMSampleBufferRef</code> 并将其发送:</p>
<pre><code> CMSampleBufferRef buffer = NULL;
CMBlockBufferRef blockBuffer;
CMBlockBufferCreateWithMemoryBlock(kCFAllocatorDefault, NULL, packet.data.size(), kCFAllocatorDefault, NULL, 0, packet.data.size(), kCMBlockBufferAssureMemoryNowFlag, &blockBuffer);
CMBlockBufferReplaceDataBytes((void*)packet.data.data(), blockBuffer, 0, packet.data.size());
CMTime duration = CMTimeMake(1024, mParameters.audioSampleRate);
CMTime pts = CMTimeMake(packet.timestamp, 1000);
CMSampleTimingInfo timing = {duration , pts, kCMTimeInvalid };
size_t sampleSizeArray = {packet.data.size()};
error = CMSampleBufferCreate(kCFAllocatorDefault, blockBuffer, true, NULL, nullptr, mContext->audioFormat, 1, 1, &timing, 1, sampleSizeArray, &buffer);
// First input buffer must have an appropriate kCMSampleBufferAttachmentKey_TrimDurationAtStart since the codec has encoder delay'
if (mContext->firstAudioFrame)
{
CFDictionaryRef dict = NULL;
dict = CMTimeCopyAsDictionary(CMTimeMake(1024, 44100), kCFAllocatorDefault);
CMSetAttachment(buffer, kCMSampleBufferAttachmentKey_TrimDurationAtStart, dict, kCMAttachmentMode_ShouldNotPropagate);
// we must trim the start time on first audio frame...
mContext->firstAudioFrame = false;
}
CMSampleBufferMakeDataReady(buffer);
BOOL ret = ;
</code></pre>
<p>我想我最怀疑的部分是我对 CMSampleBufferCreate 的调用。看来我必须传入一个样本大小数组,否则在检查作者的状态时会立即收到此错误消息:</p>
<pre><code>Error Domain=AVFoundationErrorDomain Code=-11800 "The operation could not be completed" UserInfo={NSLocalizedFailureReason=An unknown error occurred (-12735), NSLocalizedDescription=The operation could not be completed, NSUnderlyingError=0x604001e50770 {Error Domain=NSOSStatusErrorDomain Code=-12735 "(null)"}}
</code></pre>
<p>基础错误似乎是 <code>kCMSampleBufferError_BufferHasNoSampleSizes</code>。</p>
<p>我确实注意到 Apple 文档中使用 AAC 数据创建缓冲区的示例:
<a href="https://developer.apple.com/documentation/coremedia/1489723-cmsamplebuffercreate?language=objc" rel="noreferrer noopener nofollow">https://developer.apple.com/documentation/coremedia/1489723-cmsamplebuffercreate?language=objc</a> </p>
<p>在他们的示例中,他们为每个样本指定了一个长 sampleSizeArray 条目。那有必要吗?我没有这个回调的信息。在我们的 Windows 实现中,我们不需要这些数据。所以我尝试发送 packet.data.size() 作为样本大小,但这似乎不对,而且肯定不会产生令人愉悦的音频。</p>
<p>有什么想法吗?在这里调整我的调用或我应该使用不同的 API 将编码数据流混合在一起。</p>
<p>谢谢!</p></p>
<br><hr><h1><strong>Best Answer-推荐答案</ strong></h1><br>
<p><p>如果您不想转码,请不要传递 outputSetting 字典。你应该在那里传递 nil :
mContext->aacWriterInput = ;</p>
<p>本文某处对此进行了解释:
<a href="https://developer.apple.com/library/archive/documentation/AudioVideo/Conceptual/AVFoundationPG/Articles/05_Export.html" rel="noreferrer noopener nofollow">https://developer.apple.com/library/archive/documentation/AudioVideo/Conceptual/AVFoundationPG/Articles/05_Export.html</a> </p></p>
<p style="font-size: 20px;">关于ios - 使用 AVFoundation 将 AAC 音频和 h.264 视频流混合到 mp4,我们在Stack Overflow上找到一个类似的问题:
<a href="https://stackoverflow.com/questions/50142384/" rel="noreferrer noopener nofollow" style="color: red;">
https://stackoverflow.com/questions/50142384/
</a>
</p>
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