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• Using PHP-FFMPEG to crossfade audio

  18 juillet 2016, par jreikes

  I already know how to do this in FFMPEG from the command line, but was hoping I could do it all using the PHP-FFMPEG wrapper. I have two files : video.mpeg (let’s say it’s a video that’s 5 seconds in length) and fade_in.aac (this is a 0.5 second audio clip that is supposed to overlap with the beginning of video.mpeg).

  I want to crossfade audio.aac at the beginning of video.mpeg (so audio.aac starts at full volume and fades out for 0.5 seconds, video.mpeg starts at no volume and fades in during the first 0.5 seconds).

  In the command line, I would do something like the following :

  #First, strip the audio away from the video file
  
  ffmpeg -i video.mpeg audio.aac
  
  
  
  #Next, perform the crossfade operation
  
  ffmpeg -i fade_in.aac -i audio.aac -filter_complex "[a1][a2]acrossfade=d=0.5" audio_w_crossfade.aac
  
  
  
  #Finally, recombine the audio with the video file
  
  ffmpeg -i video.mpeg -i audio_w_crossfade.aac -codec copy -shortest video_w_crossfade.mpeg

  Is there a way to do this with the PHP-FFMPEG wrapper library ?

• checkasm : Serialize read_time() calls on x86

  8 octobre 2014, par Henrik Gramner

  checkasm : Serialize read_time() calls on x86
  Improves the accuracy of benchmarks, especially in short functions.
  To quote the Intel 64 and IA-32 Architectures Software Developer’s Manual :
  
  "The RDTSC instruction is not a serializing instruction. It does not necessarily
  
  wait until all previous instructions have been executed before reading the counter.
  
  Similarly, subsequent instructions may begin execution before the read operation
  
  is performed. If software requires RDTSC to be executed only after all previous
  
  instructions have completed locally, it can either use RDTSCP (if the processor
  
  supports that instruction) or execute the sequence LFENCE ;RDTSC."
  RDTSCP would accomplish the same task, but it’s only available since Nehalem.
  This change makes SSE2 a requirement to run checkasm.
  

  • [DH] tools/checkasm.c

• avfilter/af_volume : fix precision=fixed and volume=0 case

  28 février 2015, par Gilles Chanteperdrix

  avfilter/af_volume : fix precision=fixed and volume=0 case
  When precision is fixed and volume is 0, filter_frame does not
  
  perform any operation on the output buffer. This works if the
  
  output buffer has been allocated and zeroed with ff_get_audio_buffer
  
  but not if the input buffer is used as output buffer.
  Fix this by not using the input buffer as output buffer if
  
  precision is fixed and volume is 0.
  Signed-off-by : Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
  
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavfilter/af_volume.c