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• avcodec/huffman/ff_huff_gen_len_table : support skiping stat=0 entries

  9 juin 2014, par Michael Niedermayer

  avcodec/huffman/ff_huff_gen_len_table : support skiping stat=0 entries
  This is probably not the simplest solution but as this is needed for a bugfix,
  
  simplification is left for later.
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavcodec/huffman.c
  • [DH] libavcodec/huffman.h
  • [DH] libavcodec/huffyuvenc.c
  • [DH] libavcodec/utvideoenc.c

• armv6 : Accelerate ff_imdct_half for general case (mdct_bits != 6)

  11 juillet 2014, par Ben Avison

  armv6 : Accelerate ff_imdct_half for general case (mdct_bits != 6)
  The previous implementation targeted DTS Coherent Acoustics, which only
  
  requires mdct_bits == 6. This relatively small size lent itself to
  
  unrolling the loops a small number of times, and encoding offsets
  
  calculated at assembly time within the load/store instructions of each
  
  iteration.
  In the more general case (codecs such as AAC and AC3) much larger arrays
  
  are used - mdct_bits == [8, 9, 11]. The old method does not scale for
  
  these cases, so more integer registers are used with non-unrolled versions
  
  of the loops (and with some stack spillage). The postrotation filter loop
  
  is still unrolled by a factor of 2 to permit the double-buffering of some
  
  VFP registers to facilitate overlap of neighbouring iterations.
  I benchmarked the result by measuring the number of gperftools samples
  
  that hit anywhere in the AAC decoder (starting from aac_decode_frame())
  
  or specifically in ff_imdct_half_c / ff_imdct_half_vfp, for the same
  
  example AAC stream :
                    Before          After
  
                    Mean   StdDev   Mean   StdDev  Confidence  Change
  
  aac_decode_frame  2368.1 35.8     2117.2 35.3    100.0%      +11.8%
  
  ff_imdct_half_*   457.5  22.4     251.2  16.2    100.0%      +82.1%
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavcodec/arm/mdct_vfp.S

• armv6 : Accelerate ff_fft_calc for general case (nbits != 4)

  16 juillet 2014, par Ben Avison

  armv6 : Accelerate ff_fft_calc for general case (nbits != 4)
  The previous implementation targeted DTS Coherent Acoustics, which only
  
  requires nbits == 4 (fft16()). This case was (and still is) linked directly
  
  rather than being indirected through ff_fft_calc_vfp(), but now the full
  
  range from radix-4 up to radix-65536 is available. This benefits other codecs
  
  such as AAC and AC3.
  The implementaion is based upon the C version, with each routine larger than
  
  radix-16 calling a hierarchy of smaller FFT functions, then performing a
  
  post-processing pass. This pass benefits a lot from loop unrolling to
  
  counter the long pipelines in the VFP. A relaxed calling standard also
  
  reduces the overhead of the call hierarchy, and avoiding the excessive
  
  inlining performed by GCC probably helps with I-cache utilisation too.
  I benchmarked the result by measuring the number of gperftools samples that
  
  hit anywhere in the AAC decoder (starting from aac_decode_frame()) or
  
  specifically in the FFT routines (fft4() to fft512() and pass()) for the
  
  same sample AAC stream :
                Before          After
  
                Mean   StdDev   Mean   StdDev  Confidence  Change
  
  Audio decode  2245.5 53.1     1599.6 43.8    100.0%      +40.4%
  
  FFT routines  940.6  22.0     348.1  20.8    100.0%      +170.2%
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DBH] libavcodec/arm/fft_init_arm.c
  • [DBH] libavcodec/arm/fft_vfp.S