Profiling ffmpeg on Linux x86_64

In this blog post I'll elaborate on how to profile ffmpeg v0.5 on Slamd64 12.1 with the GNU profiler (gprof). Well, the profiling is meant to find the bottleneck of ffmpeg (and probably do something with it in the future).
First, rebuild the ffmpeg package with profiling enabled. This is the important excerpt from my build script:

...
./configure \
  --prefix=/usr \
  --libdir=/usr/lib64 \
  --mandir=/usr/man \
  --shlibdir=/usr/lib64 \
  --disable-debug \
...
  --enable-gprof \
  --disable-stripping \
...

#REMEMBER NOT TO STRIP THE FINAL BINARY -- SO COMMENT THE LINES BELOW
#find $PKG | xargs file | grep -e "executable" -e "shared object" | grep ELF \
#  | cut -f 1 -d : | xargs strip --strip-unneeded 2> /dev/null || true
...

Now, rebuild the ffmpeg package. Install it afterwards.

Second, run ffmpeg to transcode a DVD VOB file into an mpeg4 avi file. This is the example:

ffmpeg -i /mnt/dvd/VIDEO_TS/VTS_01_4.VOB  -f avi -vcodec mpeg4 -b 800k -g 300 -bf 2 -acodec libfaac -ab 128k outlander_01_4.avi

After the transcoding completed. We will have the profiling information in a file named gmon.out in the directory where ffmpeg was executed.

Next up, use gprof to generate a human readable statistics of the previous ffmpeg run.

gprof /usr/bin/ffmpeg gmon.out > stats.txt

At this point we have the profiling information in stats.txt. The following is snippets of the contents of my stats.txt

Flat profile:

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total          
 time   seconds   seconds    calls  ms/call  ms/call  name   
 45.46      0.20     0.20                             main
 40.92      0.38     0.18    68375     0.00     0.00  output_packet
  6.82      0.41     0.03    38468     0.00     0.00  do_audio_out
  3.41      0.43     0.02    87594     0.00     0.00  write_frame
  2.27      0.44     0.01   107095     0.00     0.00  print_report
  1.14      0.44     0.01        1     5.00     5.00  opt_format
  0.00      0.44     0.00  1982784     0.00     0.00  data_start
  0.00      0.44     0.00        7     0.00     0.00  find_codec_or_die
  0.00      0.44     0.00        7     0.00     0.00  set_context_opts
  0.00      0.44     0.00        4     0.00     0.00  opt_default
  0.00      0.44     0.00        2     0.00     0.00  opt_bitrate
  0.00      0.44     0.00        1     0.00     0.00  av_exit
  0.00      0.44     0.00        1     0.00     0.00  new_audio_stream
  0.00      0.44     0.00        1     0.00     0.00  new_video_stream
  0.00      0.44     0.00        1     0.00     0.00  opt_audio_codec
  0.00      0.44     0.00        1     0.00     0.00  opt_input_file
  0.00      0.44     0.00        1     0.00     0.00  opt_output_file
  0.00      0.44     0.00        1     0.00     0.00  opt_video_codec
  0.00      0.44     0.00        1     0.00     5.00  parse_options
  0.00      0.44     0.00        1     0.00     0.00  print_all_lib_versions
  0.00      0.44     0.00        1     0.00     0.00  show_banner

 %         the percentage of the total running time of the
time       program used by this function.
...
granularity: each sample hit covers 2 byte(s) for 2.27% of 0.44 seconds

index % time    self  children    called     name
                                                 
[1]    100.0    0.20    0.24                 main [1]
                0.18    0.05   68375/68375       output_packet [2]
                0.01    0.00  107095/107095      print_report [5]
                0.00    0.01       1/1           parse_options [7]
                0.00    0.00  715631/1982784     data_start [8]
                0.00    0.00       1/1           show_banner [21]
                0.00    0.00       1/1           av_exit [13]
-----------------------------------------------
                0.18    0.05   68375/68375       main [1]
[2]     51.1    0.18    0.05   68375         output_packet [2]
                0.03    0.01   38468/38468       do_audio_out [3]
                0.01    0.00   29892/87594       write_frame [4]
                0.00    0.00  512643/1982784     data_start [8]
...
Index by function name

  [13] av_exit                [16] opt_audio_codec         [2] output_packet
   [8] data_start             [12] opt_bitrate             [7] parse_options
   [3] do_audio_out           [11] opt_default            [20] print_all_lib_versions
   [9] find_codec_or_die       [6] opt_format              [5] print_report
   [1] main                   [17] opt_input_file         [10] set_context_opts
  [14] new_audio_stream       [18] opt_output_file        [21] show_banner
  [15] new_video_stream       [19] opt_video_codec         [4] write_frame

There is an explanation following every statistics section generated by gprof. Therefore, it shouldn't be hard to analyze the profiling result. That's it for the moment.

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