[FFmpeg-trac] #942(swresample:new): swresample leaks memory when sampling up

[FFmpeg]

#942: swresample leaks memory when sampling up
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             Reporter:  beafdefx    |                    Owner:  michael
                 Type:  defect      |                   Status:  new
             Priority:  normal      |                Component:  swresample
              Version:  git-master  |               Resolution:
             Keywords:              |               Blocked By:
             Blocking:              |  Reproduced by developer:  0
Analyzed by developer:  0           |
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Comment (by beafdefx):

 OK, I wrote a simple console program that just uses swresample to resample
 random data and included some valgrind output in the tar.gz.  The contents
 of the audio input buffer isn't important, it's the memory use with
 repeated calls to swr_convert that I'm concerned about.

 There are two defines that you can play with to alter the way the program
 executes.  OUTRATE_MULTIPLIER determines the sample rate of the output in
 relation to the input (input is locked at 16kHz).  RESAMPLE_REPS
 determines how many times swr_convert is called repeatedly.  When
 OUTRATE_MULTIPLIER is greater than 1, the program leaks.  The bigger the
 value of RESAMPLE_REPS, the more it leaks.

 DO_SWR_FREE determines if swr_free is called.  I leave this OFF for the
 purpose of measuring memory leaking because swr_free cleans up all the
 excessive memory that was used during resampling.  I'm interested in
 showing the excessive memory use during a long resampling session, for
 example, during extended playback of a song or stream.

 The included valgrind output is for 100 reps with a 2x output sample rate
 mulitpler compared to 1000 reps of the same:

 For 100 reps:

 ==45151== HEAP SUMMARY:
 ==45151==     in use at exit: 4,294,524 bytes in 42 blocks
 ==45151==   total heap usage: 51 allocs, 9 frees, 8,230,844 bytes
 allocated

 For 1000 reps:

 ==45133== HEAP SUMMARY:
 ==45133==     in use at exit: 32,966,524 bytes in 42 blocks
 ==45133==   total heap usage: 54 allocs, 12 frees, 65,478,940 bytes
 allocated

 This kind of excess usage doesn't make sense.  Also, this excess DOES NOT
 OCCUR if OUTRATE_MULITIPLER is 1 or less.  I would hope that resampling
 reuses existing buffers if possible, but it appears that is not the case.

 Hope this helps.

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Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/942#comment:5>
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