Decoder first pass complete!!

I finished the decoder and it can produce wav file output from an mp3. The good news is that is works, the bad news is that its 34 times to slow to play the audio runtime. (I have a core2 duo running at 1.83ghz.)

Since the spec pdf I found is out of date, I had to resort to looking at a couple mp3 decoders source to get the tables and algorithms. As such the python code is very close in form to the originals. I hate when it feels like im just porting code to python, but the exercise did help me understand the mp3 spec more. I plan to refactor alot of the code that was based on others decoders to make it myown and more python friendly.

Time to start cleaning up the code for readability and speed. Maybe there is enough fat to trim to get the decoding fast enough for direct playback.

Here’s some profile data:

Wed Aug 25 23:19:54 2010    stats.dat

         5725333 function calls (5724461 primitive calls) in 139.562 CPU seconds

   Ordered by: cumulative time
   List reduced from 413 to 20 due to restriction 

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
        1    0.000    0.000  139.564  139.564 :1()
        1    0.021    0.021  139.564  139.564 {execfile}
        1    0.003    0.003  139.543  139.543 ./pyMP3.py:10()
        1    0.017    0.017  122.649  122.649 ./pyMP3.py:149(decode)
      100    0.832    0.008   61.701    0.617 ./pyMP3.py:587(polyphase_synthesis)
     7200   60.602    0.008   60.719    0.008 ./pyMP3.py:609(subBandSynthesis)
      100    1.555    0.016   29.090    0.291 ./pyMP3.py:543(hybrid_synthesis)
    12800   27.348    0.002   27.535    0.002 ./pyMP3.py:563(inv_mdct)
      100   17.204    0.172   23.309    0.233 ./pyMP3.py:205(dequantize_samples)
        1    0.000    0.000   16.655   16.655 ./pyMP3.py:78(__init__)
        1    8.702    8.702   16.589   16.589 ./bitbfr.py:2(__init__)
  4052179    7.888    0.000    7.888    0.000 {ord}
   739584    5.587    0.000    5.587    0.000 {pow}
      100    0.101    0.001    4.206    0.042 ./pyMP3.py:637(decode_main_info)
      400    1.438    0.004    4.034    0.010 ./pyMP3.py:672(decode_main_data_huffman)
    65073    1.410    0.000    2.558    0.000 ./pyMP3.py:714(huffman_decoder)
      100    1.471    0.015    1.471    0.015 ./pyMP3.py:510(antialias_samples)
   295978    1.296    0.000    1.296    0.000 ./bitbfr.py:18(read_bits)
        1    0.486    0.486    1.005    1.005 ./pyMP3.py:179(write_wav)
      100    0.898    0.009    0.898    0.009 ./pyMP3.py:273(process_stereo)

Wed Aug 25 23:19:54 2010    stats.dat

         5725333 function calls (5724461 primitive calls) in 139.562 CPU seconds

   Ordered by: internal time
   List reduced from 413 to 20 due to restriction 

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
     7200   60.602    0.008   60.719    0.008 ./pyMP3.py:609(subBandSynthesis)
    12800   27.348    0.002   27.535    0.002 ./pyMP3.py:563(inv_mdct)
      100   17.204    0.172   23.309    0.233 ./pyMP3.py:205(dequantize_samples)
        1    8.702    8.702   16.589   16.589 ./bitbfr.py:2(__init__)
  4052179    7.888    0.000    7.888    0.000 {ord}
   739584    5.587    0.000    5.587    0.000 {pow}
      100    1.555    0.016   29.090    0.291 ./pyMP3.py:543(hybrid_synthesis)
      100    1.471    0.015    1.471    0.015 ./pyMP3.py:510(antialias_samples)
      400    1.438    0.004    4.034    0.010 ./pyMP3.py:672(decode_main_data_huffman)
    65073    1.410    0.000    2.558    0.000 ./pyMP3.py:714(huffman_decoder)
   295978    1.296    0.000    1.296    0.000 ./bitbfr.py:18(read_bits)
      100    0.898    0.009    0.898    0.009 ./pyMP3.py:273(process_stereo)
      100    0.832    0.008   61.701    0.617 ./pyMP3.py:587(polyphase_synthesis)
      100    0.797    0.008    0.797    0.008 ./pyMP3.py:460(reorder_samples)
   230400    0.518    0.000    0.518    0.000 {abs}
        1    0.486    0.486    1.005    1.005 ./pyMP3.py:179(write_wav)
    35205    0.318    0.000    0.318    0.000 {numpy.core.multiarray.zeros}
   115213    0.281    0.000    0.281    0.000 {method 'write' of 'file' objects}
   115209    0.237    0.000    0.237    0.000 {_struct.pack}
     7230    0.150    0.000    0.150    0.000 {method 'extend' of 'list' objects}