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• Gettting silence level to be used with silencedetect automatically

  3 mai 2017, par P. Dee

  My goal is to find the average or maximum silent level in dB to use it with silencedetect. I found volumedetect and I thought to use the histogram_ results to find the lowest dB numbers(low as in -40dB, -50dB etc.) with a high number of occurrences.

  What is a better idea ? Can it be combined with the silencedetect command, so I don’t need to enter the dB-Value at all ?

• vc-1 : Optimise parser (with special attention to ARM)

  21 juillet 2014, par Ben Avison

  vc-1 : Optimise parser (with special attention to ARM)
  The previous implementation of the parser made four passes over each input
  
  buffer (reduced to two if the container format already guaranteed the input
  
  buffer corresponded to frames, such as with MKV). But these buffers are
  
  often 200K in size, certainly enough to flush the data out of L1 cache, and
  
  for many CPUs, all the way out to main memory. The passes were :
  1) locate frame boundaries (not needed for MKV etc)
  
  2) copy the data into a contiguous block (not needed for MKV etc)
  
  3) locate the start codes within each frame
  
  4) unescape the data between start codes
  After this, the unescaped data was parsed to extract certain header fields,
  
  but because the unescape operation was so large, this was usually also
  
  effectively operating on uncached memory. Most of the unescaped data was
  
  simply thrown away and never processed further. Only step 2 - because it
  
  used memcpy - was using prefetch, making things even worse.
  This patch reorganises these steps so that, aside from the copying, the
  
  operations are performed in parallel, maximising cache utilisation. No more
  
  than the worst-case number of bytes needed for header parsing is unescaped.
  
  Most of the data is, in practice, only read in order to search for a start
  
  code, for which optimised implementations already existed in the H264 codec
  
  (notably the ARM version uses prefetch, so we end up doing both remaining
  
  passes at maximum speed). For MKV files, we know when we’ve found the last
  
  start code of interest in a given frame, so we are able to avoid doing even
  
  that one remaining pass for most of the buffer.
  In some use-cases (such as the Raspberry Pi) video decode is handled by the
  
  GPU, but the entire elementary stream is still fed through the parser to
  
  pick out certain elements of the header which are necessary to manage the
  
  decode process. As you might expect, in these cases, the performance of the
  
  parser is significant.
  To measure parser performance, I used the same VC-1 elementary stream in
  
  either an MPEG-2 transport stream or a MKV file, and fed it through avconv
  
  with -c:v copy -c:a copy -f null. These are the gperftools counts for
  
  those streams, both filtered to only include vc1_parse() and its callees,
  
  and unfiltered (to include the whole binary). Lower numbers are better :
                  Before          After
  
  File  Filtered  Mean   StdDev   Mean   StdDev  Confidence  Change
  
  M2TS  No        861.7  8.2      650.5  8.1     100.0%      +32.5%
  
  MKV   No        868.9  7.4      731.7  9.0     100.0%      +18.8%
  
  M2TS  Yes       250.0  11.2     27.2   3.4     100.0%      +817.9%
  
  MKV   Yes       149.0  12.8     1.7    0.8     100.0%      +8526.3%
  Yes, that last case shows vc1_parse() running 86 times faster ! The M2TS
  
  case does show a larger absolute improvement though, since it was worse
  
  to begin with.
  This patch has been tested with the FATE suite (albeit on x86 for speed).
  Signed-off-by : Luca Barbato <lu_zero@gentoo.org>
  

  • [DBH] libavcodec/vc1_parser.c

• Copy frame specific properties (eg. width and height)

  5 août 2014, par gkuczera

  It’s not that something is not working, I just can’t figure out how to copy frame props (eg. height and width) after usage of sws_scale function - this function doesn’t copy them into the destination frame).

  Why I need this ? My frame after scaling is becoming the input for the filter, and it’s source props have to be specified to specific numbers, not like it accepts everything (so a frame with width and height equal to zero - which I get after scaling - is not an option).

  I tried to use

  av_frame_copy_props

  but even in this function’s description, they mentioned that it will not do this.

  Here is the code :

  AVFrame* tOwnersFrame = pOwner->getFrame();
  
  AVFrame* tResizedFrame = avcodec_alloc_frame();
  
  int tResizedFrameWidth = pMaxFrameWidth;
  
  int tResizedFrameHeight = pMaxFrameHeight;
  
  
  
  if (!tResizedFrame)
  
  {
  
      cout << "Couldn't allocate the frame!" << endl;
  
      return;
  
  }
  
  
  
  uint8_t* tBuffer;
  
  int tBytesNeeded;
  
  
  
  tBytesNeeded = avpicture_get_size(PIX_FMT_RGB24, tResizedFrameWidth, tResizedFrameHeight);
  
  tBuffer = (uint8_t*)av_malloc(tBytesNeeded * sizeof(uint8_t));
  
  avpicture_fill((AVPicture*)tResizedFrame, tBuffer, PIX_FMT_RGB24, tResizedFrameWidth, tResizedFrameHeight);
  
  
  
  mSwsContext = sws_getCachedContext(mSwsContext, pOwner->getFrameWidth(), pOwner->getFrameHeight(), AV_PIX_FMT_BGR24, tResizedFrameWidth, tResizedFrameHeight, PIX_FMT_RGB24, SWS_BILINEAR, NULL, NULL, NULL);
  
  sws_scale(mSwsContext, (const uint8_t* const *)tOwnersFrame->data, tOwnersFrame->linesize, 0, pOwner->getFrameHeight(), tResizedFrame->data, tResizedFrame->linesize);
  
  cout << "FramesMerger::resizeFrameMax - arg frame size: " << pOwner->getFrame()->width << ", " << pOwner->getFrame()->height << endl;
  
  cout << "FramesMerger::resizeFrameMax - resized frame size: " << tResizedFrame->width << ", " << tResizedFrame->height << endl;