九江网站排名,西宁思帽网站建设,godaddy,改wordpress的wp_admin关于AAC音频格式基本情况#xff0c;可参考维基百科http://en.wikipedia.org/wiki/Advanced_Audio_Coding AAC音频格式分析 AAC音频格式有ADIF和ADTS#xff1a; ADIF#xff1a;Audio Data Interchange Format 音频数据交换格式。这种格式的特征是可以确定的找到这个音频数… 关于AAC音频格式基本情况可参考维基百科http://en.wikipedia.org/wiki/Advanced_Audio_Coding   AAC音频格式分析 AAC音频格式有ADIF和ADTS  ADIFAudio Data Interchange Format 音频数据交换格式。这种格式的特征是可以确定的找到这个音频数据的开始不需进行在音频数据流中间开始的解码即它的解码必须在明确定义的开始处进行。故这种格式常用在磁盘文件中。  ADTSAudio Data Transport Stream 音频数据传输流。这种格式的特征是它是一个有同步字的比特流解码可以在这个流中任何位置开始。它的特征类似于mp3数据流格式。  简单说ADTS可以在任意帧解码也就是说它每一帧都有头信息。ADIF只有一个统一的头所以必须得到所有的数据后解码。且这两种的header的格式也是不同的目前一般编码后的和抽取出的都是ADTS格式的音频流。  语音系统对实时性要求较高基本是这样一个流程采集音频数据本地编码数据上传服务器处理数据下发本地解码  ADTS是帧序列本身具备流特征在音频流的传输与处理方面更加合适。     ADTS帧结构 header body ADTS帧首部结构 序号 域 长度bits 说明 1 Syncword 12 all bits must be 1 2 MPEG version 1 0 for MPEG-4, 1 for MPEG-2 3 Layer 2 always 0 4 Protection Absent 1 et to 1 if there is no CRC and 0 if there is CRC 5 Profile 2 the MPEG-4 Audio Object Type minus 1 6 MPEG-4 Sampling Frequency Index 4 MPEG-4 Sampling Frequency Index (15 is forbidden) 7 Private Stream 1 set to 0 when encoding, ignore when decoding 8 MPEG-4 Channel Configuration 3 MPEG-4 Channel Configuration (in the case of 0, the channel configuration is sent via an inband PCE) 9 Originality 1 set to 0 when encoding, ignore when decoding 10 Home 1 set to 0 when encoding, ignore when decoding 11 Copyrighted Stream 1 set to 0 when encoding, ignore when decoding 12 Copyrighted Start 1 set to 0 when encoding, ignore when decoding 13 Frame Length 13 this value must include 7 or 9 bytes of header length: FrameLength (ProtectionAbsent 1 ? 7 : 9) size(AACFrame) 14 Buffer Fullness 11 buffer fullness 15 Number of AAC Frames 2 number of AAC frames (RDBs) in ADTS frame minus 1, for maximum compatibility always use 1 AAC frame per ADTS frame 16 CRC 16 CRC if protection absent is 0 MPEG-4 Audio Company: ISOSamples: http://samples.mplayerhq.hu/MPEG-4/Samples: http://samples.mplayerhq.hu/A-codecs/AAC/Samples: sample repo at standards.iso.orgSample Docs: sample docs Specification links: MPEG-4 Audio: ISO/IEC 14496-3:2009Conformance: ISO/IEC 14496-26:2010 Contents  [hide]  1 MPEG-4 Audio2 Subparts3 Audio Specific Config4 Audio Object Types5 Sampling Frequencies6 Channel Configurations MPEG-4 Audio MPEG-4 includes a system for handling a diverse group of audio formats in a uniform matter. Each format is assigned a unique Audio Object Type (AOT) to represent it. The common format Global header shared by all AOTs is called the Audio Specific Config.  Subparts Subpart 0: OverviewSubpart 1: Main (Systems Interaction)Subpart 2: Speech coding - HVXCSubpart 3: Speech coding - CELPSubpart 4: General Audio coding (GA) - AAC, TwinVQ, BSACSubpart 5: Structured Audio (SA)Subpart 6: Text To Speech Interface (TTSI)Subpart 7: Parametric Audio Coding - HILNSubpart 8: Parametric coding for high quality audio - SSC (and Parametric Stereo)Subpart 9: MPEG-1/2 Audio in MPEG-4Subpart 10: Lossless coding of oversampled audio - DSTSubpart 11: Audio lossless coding - ALSSubpart 12: Scalable lossless coding - SLS Audio Specific Config The Audio Specific Config is the global header for MPEG-4 Audio: 5 bits: object type if (object type 31)6 bits 32: object type 4 bits: frequency index if (frequency index 15)24 bits: frequency 4 bits: channel configuration var bits: AOT Specific ConfigAudio Object Types MPEG-4 Audio Object Types: 0: Null 1: AAC Main2: AAC LC (Low Complexity)3: AAC SSR (Scalable Sample Rate)4: AAC LTP (Long Term Prediction)5: SBR (Spectral Band Replication)6: AAC Scalable7: TwinVQ8: CELP (Code Excited Linear Prediction)9: HXVC (Harmonic Vector eXcitation Coding)10: Reserved11: Reserved12: TTSI (Text-To-Speech Interface)13: Main Synthesis14: Wavetable Synthesis15: General MIDI16: Algorithmic Synthesis and Audio Effects17: ER (Error Resilient) AAC LC18: Reserved19: ER AAC LTP20: ER AAC Scalable21: ER TwinVQ22: ER BSAC (Bit-Sliced Arithmetic Coding)23: ER AAC LD (Low Delay)24: ER CELP25: ER HVXC26: ER HILN (Harmonic and Individual Lines plus Noise)27: ER Parametric28: SSC (SinuSoidal Coding)29: PS (Parametric Stereo)30: MPEG Surround31: (Escape value)32: Layer-133: Layer-234: Layer-335: DST (Direct Stream Transfer)36: ALS (Audio Lossless)37: SLS (Scalable LosslesS)38: SLS non-core39: ER AAC ELD (Enhanced Low Delay)40: SMR (Symbolic Music Representation) Simple41: SMR Main42: USAC (Unified Speech and Audio Coding) (no SBR)43: SAOC (Spatial Audio Object Coding)44: LD MPEG Surround45: USAC Sampling Frequencies There are 13 supported frequencies: 0: 96000 Hz1: 88200 Hz2: 64000 Hz3: 48000 Hz4: 44100 Hz5: 32000 Hz6: 24000 Hz7: 22050 Hz8: 16000 Hz9: 12000 Hz10: 11025 Hz11: 8000 Hz12: 7350 Hz13: Reserved14: Reserved15: frequency is written explictly Channel Configurations These are the channel configurations: 0: Defined in AOT Specifc Config1: 1 channel: front-center2: 2 channels: front-left, front-right3: 3 channels: front-center, front-left, front-right4: 4 channels: front-center, front-left, front-right, back-center5: 5 channels: front-center, front-left, front-right, back-left, back-right6: 6 channels: front-center, front-left, front-right, back-left, back-right, LFE-channel7: 8 channels: front-center, front-left, front-right, side-left, side-right, back-left, back-right, LFE-channel8-15: Reserved