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• aaccoder : rewrite PNS implementation

  6 septembre 2015, par Rostislav Pehlivanov

  aaccoder : rewrite PNS implementation
  This commit rewrites the PNS implementation and significantly
  
  improves sonic quality.
  The previous implementation marked an incredibly big amount
  
  of SFBs to predict when there was no need for this and this
  
  resulted in quite a large amount of artifacts. Also the
  
  quantization was incorrect (av_clip(4+log2f(...))) which
  
  led to 3x the intensity for PNS values leading to even more
  
  artifacts.
  This commit rewrites the PNS search function and introduces
  
  a major change : the PNS values are synthesized and are compared
  
  to the current coefficients in addition to passing through
  
  the revised checks to see whether PNS can be used.
  This decreases distortions and makes the current PNS implementation
  
  mainly focused on replacing any low-power non-zero bands as well
  
  as adding any zeroed bands back.
  The current encoder’s performance is enough (especially with
  
  IS) so PNS isn’t really required except to fill in the occasional
  
  few bands as well as extend any zeroed high frequency, so this
  
  combination which is already enabled by default works
  
  to get as much quality as it can within the bits allowed.
  Signed-off-by : Rostislav Pehlivanov <atomnuker@gmail.com>
  

  • [DH] libavcodec/aaccoder.c

• aacenc_pred : rework the way prediction is done

  29 août 2015, par Rostislav Pehlivanov

  aacenc_pred : rework the way prediction is done
  This commit completely alters the algorithm of prediction.
  
  The original commit which introduced prediction was completely
  
  incorrect to even remotely care about what the actual coefficients
  
  contain or whether any options were enabled. Not my actual fault.
  This commit treats prediction the way the decoder does and expects
  
  to do : like lossy encryption. Everything related to prediction now
  
  happens at the very end but just before quantization and encoding
  
  of coefficients. On the decoder side, prediction happens before
  
  anything has had a chance to even access the coefficients.
  Also the original implementation had problems because it actually
  
  touched the band_type of special bands which already had their
  
  scalefactor indices marked and it’s a wonder the asserion wasn’t
  
  triggered when transmitting those.
  Overall, this now drastically increases audio quality and you should
  
  think about enabling it if you don’t plan on playing anything encoded
  
  on really old low power ultra-embedded devices since they might not
  
  support decoding of prediction or AAC-Main. Though the specifications
  
  were written ages ago and as times change so do the FLOPS.
  Signed-off-by : Rostislav Pehlivanov <atomnuker@gmail.com>
  

  • [DH] libavcodec/aac.h
  • [DH] libavcodec/aaccoder.c
  • [DH] libavcodec/aacenc.c
  • [DH] libavcodec/aacenc.h
  • [DH] libavcodec/aacenc_pred.c
  • [DH] libavcodec/aacenc_pred.h

• Correct recording time of the first frame of a video

  27 juillet 2017, par Vítor Cézar

  How do I get the correct time of the first frame recorded on a video ? I executed the command

  ffprobe -v error -show_streams [file_path]

  and got these values of timecode and creation time for the first stream :

  TAG:creation_time=2017-07-26T16:48:10.000000Z
  
  TAG:language=eng
  
  TAG:handler_name=   GoPro AVC
  
  TAG:encoder=GoPro AVC encoder
  
  TAG:timecode=17:21:54:28

  The problem is that the video started being recorded on 16:48:11:504 and neither timecode nor creation time shows this value. If possible I need the precision on milliseconds.