音頻解碼 Audio Converter
需求
iOS中將壓縮音頻數據(如AAC)進行解碼以獲得原始音頻數據類型:線性PCM.ios
本例最終實現的是經過Audio Queue採集到AAC壓縮數據,將其解碼爲PCM數據,並將解碼後的PCM數據以錄製的形式保存在沙盒中.可調整解碼後採樣率,解碼器類型等參數.git
本例可拓展,不單單解碼AAC音頻數據流,還能夠是音頻文件,視頻文件中的音頻等等.github
實現原理
利用Audio Toolbox Framework中的Audio Converter能夠實現音頻數據解碼,即將AAC數據轉爲原始音頻數據PCM.數組
閱讀前提:
- Core Audio基本原理:簡書,掘金,博客
- Audio Queue解析:掘金,簡書,博客
- Audio Queue實戰:簡書,博客, 掘金
- 音頻文件錄製:簡書,掘金,博客
- 音視頻基礎知識
- C,C++基本知識
GitHub地址(附代碼) : 音頻解碼
簡書地址 : 音頻解碼
掘金地址 : 音頻解碼
博客地址 : 音頻解碼
1.初始化
1.1. 初始化解碼器
初始化解碼器實例, 經過指定原始數據格式,最終解碼後的格式,採樣率,以及使用硬編仍是軟編,如下是具體步驟.bash
- (instancetype)initWithSourceFormat:(AudioStreamBasicDescription)sourceFormat destFormatID:(AudioFormatID)destFormatID sampleRate:(float)sampleRate isUseHardwareDecode:(BOOL)isUseHardwareDecode {
if (self = [super init]) {
mSourceFormat = sourceFormat;
mAudioConverter = [self configureDecoderBySourceFormat:sourceFormat
destFormat:&mDestinationFormat
destFormatID:destFormatID
sampleRate:sampleRate
isUseHardwareDecode:isUseHardwareDecode];
}
return self;
}
複製代碼
1.2. 配置解碼後ASBD音頻流信息
AudioStreamBasicDescription destinationFormat = {0};
destinationFormat.mSampleRate = sampleRate;
if (destFormatID != kAudioFormatLinearPCM) {
NSLog(@"Not get compression format after decoding !");
return NULL;
} else {
destinationFormat.mFormatID = destFormatID;
destinationFormat.mChannelsPerFrame = sourceFormat.mChannelsPerFrame;
destinationFormat.mFormatID = kAudioFormatLinearPCM;
destinationFormat.mFormatFlags = (kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked);
destinationFormat.mFramesPerPacket = kXDXAudioPCMFramesPerPacket;
destinationFormat.mBitsPerChannel = KXDXAudioBitsPerChannel;
destinationFormat.mBytesPerFrame = destinationFormat.mBitsPerChannel / 8 *destinationFormat.mChannelsPerFrame;
destinationFormat.mBytesPerPacket = destinationFormat.mBytesPerFrame * destinationFormat.mFramesPerPacket;
destinationFormat.mReserved = 0;
}
memcpy(destFormat, &destinationFormat, sizeof(AudioStreamBasicDescription));
複製代碼
對音頻作解碼操做,實際就是將壓縮數據格式如AAC格式轉爲線性PCM原始音頻數據,經過kAudioFormatProperty_FormatInfo屬性能夠自動獲取指定音頻格式的參數信息.app
1.3. 選擇解碼器類型
AudioClassDescription結構體描述了系統使用音頻解碼器信息,其中最重要的就是使用硬編或軟編。而後解碼器的數量，即數組的個數，由當前的聲道數決定。函數
//獲取解碼器的描述信息
AudioClassDescription *audioClassDesc = [self getAudioCalssDescriptionWithType:destFormatID fromManufacture:kAppleHardwareAudioCodecManufacturer];
...
- (AudioClassDescription *)getAudioCalssDescriptionWithType:(AudioFormatID)type fromManufacture:(uint32_t)manufacture {
static AudioClassDescription desc;
UInt32 decoderSpecific = type;
UInt32 size;
OSStatus status = AudioFormatGetPropertyInfo(kAudioFormatProperty_Decoders,
sizeof(decoderSpecific),
&decoderSpecific,
&size);
if (status != noErr) {
NSLog(@"Error！：硬解碼AAC get info 失敗, status= %d", (int)status);
return nil;
}
//計算aac解碼器的個數
unsigned int count = size / sizeof(AudioClassDescription);
//建立一個包含count個解碼器的數組
AudioClassDescription description[count];
//將知足aac解碼的解碼器的信息寫入數組
status = AudioFormatGetProperty(kAudioFormatProperty_Encoders,
sizeof(decoderSpecific),
&decoderSpecific,
&size,
&description);
if (status != noErr) {
NSLog(@"Error！：硬解碼AAC get propery 失敗, status= %d", (int)status);
return nil;
}
for (unsigned int i = 0; i < count; i++) {
if (type == description[i].mSubType && manufacture == description[i].mManufacturer) {
desc = description[i];
return &desc;
}
}
return nil;
}
複製代碼
注意：硬解即利用設備GPU硬件完成高效解碼，下降CPU消耗. 軟解就是傳統的經過CPU計算。post
1.4. 建立解碼器
AudioConverterNewSpecific: 經過指定解碼器來建立audio converter實例對象.第3,4個 分別是解碼器的數量與解碼器描述,同上,與聲道數保持一致.ui
// Create the AudioConverterRef.
AudioConverterRef converter = NULL;
if (![self checkError:AudioConverterNewSpecific(&sourceFormat, &destinationFormat, destinationFormat.mChannelsPerFrame, audioClassDesc, &converter) withErrorString:@"Audio Converter New failed"]) {
return NULL;
}else {
printf("Audio converter create successful \n");
}
複製代碼
2.解碼
2.1. 計算解碼數據大小
注意,當使用Audio Convert不管作編解碼,每次都須要1024個採樣點才能完成一次轉換,此值是固定的.
根據解碼器的採樣點,計算解碼出音頻數據的大小.由於線性PCM的數據能夠經過公式算出,即數據包數量*聲道數*每一個數據包中字節數.編碼
// Note: audio convert must set 1024.
UInt32 ioOutputDataPackets = kIOOutputDataPackets;
UInt32 outputBufferSize = (UInt32)(ioOutputDataPackets * destFormat.mChannelsPerFrame * destFormat.mBytesPerFrame);
複製代碼
2.2. 爲解碼後音頻數據預分配內存
咱們能夠將2.1中算出的size爲這個Buffer list分配內存.
// Set up output buffer list.
// Set up output buffer list.
AudioBufferList fillBufferList = {0};
fillBufferList.mNumberBuffers = 1;
fillBufferList.mBuffers[0].mNumberChannels = destFormat.mChannelsPerFrame;
fillBufferList.mBuffers[0].mDataByteSize = outputBufferSize;
fillBufferList.mBuffers[0].mData = malloc(outputBufferSize * sizeof(char));
複製代碼
2.3. 解碼音頻數據
解析AudioConverterFillComplexBuffer:用來解碼音頻數據.同時須要指定回調函數(C語言函數),
第二個參數即指定回調函數,此回調函數中主要作的是爲即將解碼的數據進行賦值,即咱們要把原始音頻數據賦值給回調函數中的ioData參數,這是咱們在解碼前最後一次控制原始音頻數據,此回調函數執行後即完成了解碼的過程,新的數據會填充到第五個參數中,也就是咱們上面預約義的fillBufferList.
userInfo: 自定義一個結構體,用來與解碼回調函數間交互以傳遞數據.在這裏是將原始音頻數據信息傳給解碼回調函數中.ioOutputDataPackets: 填入函數中時表示原始音頻數據包的數量,而函數調用完成時表示轉換後輸出的音頻數據包總數,注意,當咱們作解碼時,輸出確定爲PCM類型數據,因此須要提供1024個AAC採樣點.而作編碼時會將PCM數據壓縮成不少音頻數據包,僅僅須要1個完整的PCM數據包便可.outputPacketDescriptions: 轉換完成後,若是此參數非空,表示轉換器輸出使用的音頻數據包描述,它必須提早分配好內存,以讓轉換器賦值到其中.
最終,咱們將轉換後獲得的AAC數據以回調函數的形式傳給調用者.
OSStatus DecodeConverterComplexInputDataProc(AudioConverterRef inAudioConverter,
UInt32 *ioNumberDataPackets,
AudioBufferList *ioData,
AudioStreamPacketDescription **outDataPacketDescription,
void *inUserData) {
XDXConverterInfoType *info = (XDXConverterInfoType *)inUserData;
if (info->sourceDataSize <= 0) {
ioNumberDataPackets = 0;
return -1;
}
*outDataPacketDescription = &info->packetDesc;
(*outDataPacketDescription)[0].mStartOffset = 0;
(*outDataPacketDescription)[0].mDataByteSize = info->sourceDataSize;
(*outDataPacketDescription)[0].mVariableFramesInPacket = 0;
ioData->mNumberBuffers = 1;
ioData->mBuffers[0].mData = info->sourceBuffer;
ioData->mBuffers[0].mNumberChannels = info->sourceChannelsPerFrame;
ioData->mBuffers[0].mDataByteSize = info->sourceDataSize;
return noErr;
}
- (void)decodeFormatByConverter:(AudioConverterRef)audioConverter sourceBuffer:(void *)sourceBuffer sourceBufferSize:(UInt32)sourceBufferSize sourceFormat:(AudioStreamBasicDescription)sourceFormat dest:(AudioStreamBasicDescription)destFormat completeHandler:(void(^)(AudioBufferList *destBufferList, UInt32 outputPackets, AudioStreamPacketDescription *outputPacketDescriptions))completeHandler {
...
XDXConverterInfoType userInfo = {0};
userInfo.sourceBuffer = sourceBuffer;
userInfo.sourceDataSize = sourceBufferSize;
userInfo.sourceChannelsPerFrame = sourceFormat.mChannelsPerFrame;
userInfo.packetDesc.mDataByteSize = (UInt32)sourceBufferSize;
userInfo.packetDesc.mStartOffset = 0;
userInfo.packetDesc.mVariableFramesInPacket = 0;
AudioStreamPacketDescription outputPacketDesc;
OSStatus status = AudioConverterFillComplexBuffer(audioConverter,
DecodeConverterComplexInputDataProc,
&userInfo,
&ioOutputDataPackets,
&fillBufferList,
&outputPacketDesc);
// if interrupted in the process of the conversion call, we must handle the error appropriately
if (status != noErr) {
if (status == kAudioConverterErr_HardwareInUse) {
printf("Audio Converter returned kAudioConverterErr_HardwareInUse!\n");
} else {
if (![self checkError:status withErrorString:@"AudioConverterFillComplexBuffer error!"]) {
return;
}
}
} else {
if (ioOutputDataPackets == 0) {
// This is the EOF condition.
status = noErr;
}
if (completeHandler) {
completeHandler(&fillBufferList, ioOutputDataPackets, &outputPacketDesc);
}
}
}
複製代碼
3. 模塊對接
由於音頻解碼要依賴音頻採集,因此咱們這裏以audio unit採集爲例做示範,即便用audio unit採集pcm數據而後使用此模塊解碼獲得aac數據.如需瞭解請參考以下連接
- GitHub地址(附代碼) : Audio Unit Capture
- 簡書地址 : Audio Unit Capture
- 掘金地址 : Audio Unit Capture
- 博客地址 : Audio Unit Capture
3.1. 初始化解碼器
以下,在音頻採集的類中聲明一個解碼器實例變量,而後初始化它. 僅僅須要設置原始數據格式,解碼後的格式,採樣率,使用硬編,軟編便可.
@property (nonatomic, strong) XDXAduioDecoder *audioDecoder;
...
// audio decode: aac->pcm
self.audioDecoder = [[XDXAduioDecoder alloc] initWithSourceFormat:m_audioInfo->mDataFormat
destFormatID:kAudioFormatLinearPCM
sampleRate:48000
isUseHardwareDecode:YES];
複製代碼
3.2. 解碼音頻數據
在Audio Queue採集AAC音頻數據的回調中將AAC數據送入解碼器,而後在回調函數中將獲得的PCM數據其寫入文件.
注意: 直接用Audio Queue採集AAC類型音頻數據,實際系統在其內部作了一次轉換,即直接採集其實只能採原始PCM數據,直接用Audio Queue設置採集AAC至關於系統在內部爲咱們作了一次轉換.
static void CaptureAudioDataCallback(void * inUserData,
AudioQueueRef inAQ,
AudioQueueBufferRef inBuffer,
const AudioTimeStamp * inStartTime,
UInt32 inNumPackets,
const AudioStreamPacketDescription* inPacketDesc) {
XDXAudioQueueCaptureManager *instance = (__bridge XDXAudioQueueCaptureManager *)inUserData;
[instance.audioDecoder decodeAudioWithSourceBuffer:inBuffer->mAudioData
sourceBufferSize:inBuffer->mAudioDataByteSize
completeHandler:^(AudioBufferList * _Nonnull destBufferList, UInt32 outputPackets, AudioStreamPacketDescription * _Nonnull outputPacketDescriptions) {
if (instance.isRecordVoice) {
[[XDXAudioFileHandler getInstance] writeFileWithInNumBytes:destBufferList->mBuffers->mDataByteSize
ioNumPackets:outputPackets
inBuffer:destBufferList->mBuffers->mData
inPacketDesc:outputPacketDescriptions];
}
free(destBufferList->mBuffers->mData);
}];
if (instance.isRunning) {
AudioQueueEnqueueBuffer(inAQ, inBuffer, 0, NULL);
}
}
複製代碼
4. 文件錄製
此部分可參考另外一篇文章: 音頻文件錄製
- 簡書地址 : Audio File Record
- 掘金地址 : Audio File Record
- 博客地址 : Audio File Record
5. 釋放解碼器資源
如需釋放內存,請保證解碼器工做完全結束後再釋放內存.
- (void)freeEncoder {
if (mAudioConverter) {
AudioConverterDispose(mAudioConverter);
mAudioConverter = NULL;
}
}
複製代碼
相關文章
- 1. 音頻編碼 Audio Converter
- 2. EZ CD Audio Converter
- 3. iOS 音視頻開發：Audio Unit播放FFmpeg解碼的音頻
- 4. 【入門Audio音頻】必瞭解：Audio音頻格式介紹
- 5. HTML5 Audio(音頻)
- 6. Linux audio 音頻
- 7. HTML 音頻(Audio)
- 8. NoteBurner iTunes DRM Audio Converter for Mac(Mac音頻轉換器)
- 9. TunesKit Audio Converter for Mac(音頻DRM去除轉換器)
- 10. iOS音頻---Audio Queue
- 更多相關文章...
- • XML 編碼 - XML 教程
- • HTTP狀態碼 - HTTP 教程
- • Scala 中文亂碼解決
- • IntelliJ IDEA代碼格式化設置
相關標籤/搜索
每日一句
-
每一个你不满意的现在，都有一个你没有努力的曾经。
歡迎關注本站公眾號,獲取更多信息
相關文章
- 1. 音頻編碼 Audio Converter
- 2. EZ CD Audio Converter
- 3. iOS 音視頻開發：Audio Unit播放FFmpeg解碼的音頻
- 4. 【入門Audio音頻】必瞭解：Audio音頻格式介紹
- 5. HTML5 Audio(音頻)
- 6. Linux audio 音頻
- 7. HTML 音頻(Audio)
- 8. NoteBurner iTunes DRM Audio Converter for Mac(Mac音頻轉換器)
- 9. TunesKit Audio Converter for Mac(音頻DRM去除轉換器)
- 10. iOS音頻---Audio Queue