faac源码分析之faacEncOpen

faacEncOpen的代码流程图如下所示：

主要包括初始化解码器句柄以及使用的默认参数，最后的是各个功能模块的初始化，主要是分配内存，初始化一些系数表。

faacEncHandle FAACAPI faacEncOpen(unsigned long sampleRate,unsigned int numChannels,unsigned long *inputSamples,unsigned long *maxOutputBytes){unsigned int channel;faacEncHandle hEncoder;*inputSamples = FRAME_LEN*numChannels;*maxOutputBytes = (6144/8)*numChannels;#ifdef DRM*maxOutputBytes += 1; /* for CRC */#endifhEncoder = (faacEncStruct*)AllocMemory(sizeof(faacEncStruct));SetMemory(hEncoder, 0, sizeof(faacEncStruct));hEncoder->numChannels = numChannels;hEncoder->sampleRate = sampleRate;hEncoder->sampleRateIdx = GetSRIndex(sampleRate);/* Initialize variables to default values */hEncoder->frameNum = 0;hEncoder->flushFrame = 0;/* Default configuration */hEncoder->config.version = FAAC_CFG_VERSION;hEncoder->config.name = libfaacName;hEncoder->config.copyright = libCopyright;hEncoder->config.mpegVersion = MPEG4;hEncoder->config.aacObjectType = LOW;hEncoder->config.allowMidside = 0;hEncoder->config.useLfe = 0;hEncoder->config.useTns = 0;hEncoder->config.bitRate = 48000; /* default bitrate / channel */hEncoder->config.bandWidth = 32000/*bwfac * hEncoder->sampleRate*/;/* if (hEncoder->config.bandWidth > bwbase)hEncoder->config.bandWidth = bwbase;*/hEncoder->config.quantqual = 100;hEncoder->config.psymodellist = (psymodellist_t *)psymodellist;hEncoder->config.psymodelidx = 0;hEncoder->psymodel =hEncoder->config.psymodellist[hEncoder->config.psymodelidx].model;hEncoder->config.shortctl = SHORTCTL_NORMAL;/* default channel map is straight-through */for( channel = 0; channel < 64; channel++ )hEncoder->config.channel_map[channel] = channel;/*by default we have to be compatible with all previous softwarewhich assumes that we will generate ADTS/AV*/hEncoder->config.outputFormat = 0;//raw without adts/*be compatible with software which assumes 24bit in 32bit PCM*/hEncoder->config.inputFormat = FAAC_INPUT_16BIT;/* find correct sampling rate depending parameters */hEncoder->srInfo = &srInfo[hEncoder->sampleRateIdx];for (channel = 0; channel < numChannels; channel++) {hEncoder->coderInfo[channel].prev_window_shape = SINE_WINDOW;hEncoder->coderInfo[channel].window_shape = SINE_WINDOW;hEncoder->coderInfo[channel].block_type = ONLY_SHORT_WINDOW;hEncoder->coderInfo[channel].num_window_groups = 1;hEncoder->coderInfo[channel].window_group_length[0] = 8;/* FIXME: Use sr_idx here */hEncoder->coderInfo[channel].max_pred_sfb = GetMaxPredSfb(hEncoder->sampleRateIdx);hEncoder->sampleBuff[channel] = NULL;hEncoder->nextSampleBuff[channel] = NULL;hEncoder->next2SampleBuff[channel] = NULL;hEncoder->ltpTimeBuff[channel] = (double*)AllocMemory(2*BLOCK_LEN_LONG*sizeof(double));SetMemory(hEncoder->ltpTimeBuff[channel], 0, 2*BLOCK_LEN_LONG*sizeof(double));}/* Initialize coder functions */fft_initialize( &hEncoder->fft_tables );//fast fourier transform initializehEncoder->psymodel->PsyInit(&hEncoder->gpsyInfo, hEncoder->psyInfo, hEncoder->numChannels,hEncoder->sampleRate, hEncoder->srInfo->cb_width_long,hEncoder->srInfo->num_cb_long, hEncoder->srInfo->cb_width_short,hEncoder->srInfo->num_cb_short);FilterBankInit(hEncoder);TnsInit(hEncoder);LtpInit(hEncoder);PredInit(hEncoder);AACQuantizeInit(hEncoder->coderInfo, hEncoder->numChannels,&(hEncoder->aacquantCfg));HuffmanInit(hEncoder->coderInfo, hEncoder->numChannels);/* Return handle */return hEncoder;}