mirror of https://github.com/mstorsjo/fdk-aac.git
e499f9485e
Operating the FDK encoder in A2DP with variable bitrate mode configuration resulted in unexpected encoder return value AACENC_ENCODE_ERROR. Due to peak bitrate restriction the encoder quite often runs into requantization. In case the bitrate constraint is not fulfilled, the so-called crash recovery is used as final emergency step. The crash recovery reduces the overall bit consumption considering the given number of bits to be saved. The bit difference is extracted from audio element structures. In VBR mode the element wise bit consumption state was not updated since there is typically no bitrate limitation required. The patch solves the choppy audio problems and increases audio quality for AAC VBR encoding. The changes in FDKaacEnc_QCMain() ensure that audio element bit info is always updated. This is achieved by always calling FDKaacEnc_BitResRedistribution() and FDKaacEnc_prepareBitDistribution() with maxBitsPerFrame variable as total bits parameter. Furthermore, VBR assumes a certain target bitrate which is used for internal configuration and limitations. In case the peak bitrate parameter is less than the VBR mode target bitrate the maximum of both bitrate configurations was used. The function FDKaacEnc_AdjustVBRBitrateMode() is added to adjust the encoder internal VBR mode to a desired target bitrate less than given peak bitrate. It is possible that the peak bitrate is very close to the desired target bitrate. The virtual available bitreservoir is quite low and the encoder would run quite often into requantization with needless audio quality reduction. In such a configuration, it is a better choice to use the CBR targeted threshold adaption to avoid audio quality reduction. In FDKaacEnc_Initialize(), there was already a bitResMode selection depending on available bitreservoir for CBR. This selection will now also be used for VBR. In case the bitResMode is AACENC_BR_MODE_FULL and VBR mode is selected, the VBR threshold adaption is used. Otherwise, CBR threshold adaption strategy is used and therefore, no unnecessary fill bits are written. Bug: 161400526 Test: see bug Change-Id: I1865f817180150da6add2623a64f1a102622784a |
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