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• avcodec/mpeg4audio : add newer channel_coding mappings

  10 juin 2020, par Jan Ekström

  avcodec/mpeg4audio : add newer channel_coding mappings
  Additionally, add comments regarding their definitions. Based on
  
  ARIB STD-B32, which bases on 14496-3:2009 and 14496-3:2009/AMD4.
  

  • [DH] libavcodec/mpeg4audio.c
  • [DH] libavcodec/mpeg4audio.h

• avfilter/af_headphone : Simplify parsing channel mapping string

  27 août 2020, par Andreas Rheinhardt

  avfilter/af_headphone : Simplify parsing channel mapping string
  When parsing the channel mapping string (a string containing '|'
  
  delimited tokens each of which is supposed to contain a channel name
  
  like "FR"), the old code would at each step read up to seven uppercase
  
  characters from the input string and give this to
  
  av_get_channel_layout() to parse. The returned layout is then checked
  
  for being a layout with a single channel set by computing its logarithm.
  Besides being overtly complicated this also has the drawback of relying
  
  on the assumption that every channel name consists of at most seven
  
  uppercase letters only ; but said assumption is wrong : The abbreviation
  
  of the second low frequency channel is LFE2. Furthermore it treats
  
  garbage like "FRfoo" as valid channel.
  This commit changes this by using av_get_channel_layout() directly ;
  
  furthermore, av_get_channel_layout_nb_channels() (which uses popcount)
  
  is used to find out the number of channels instead of the custom code
  
  to calculate the logarithm.
  (As a consequence, certain other formats to specify the channel layouts
  
  are now accepted (like the hex versions of av_get_channel_layout()) ; but
  
  this is actually not bad at all.)
  Reviewed-by : Paul B Mahol <onemda@gmail.com>
  
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavfilter/af_headphone.c

• avfilter/af_headphone : Use uint64_t for channel mapping

  24 août 2020, par Andreas Rheinhardt

  avfilter/af_headphone : Use uint64_t for channel mapping
  The headphone filter has an option for the user to specify an assignment
  
  of inputs to channels (or from pairs of channels of the second input to
  
  channels). Up until now, these channels were stored in an int containing
  
  the logarithm of the channel layout. Yet it is not the logarithm that is
  
  used lateron and so a retransformation was necessary. Therefore this
  
  commit simply stores the uint64_t as is, avoiding the retransformation.
  This also has the advantage that unset channels (whose corresponding
  
  entry is zero) can't be mistaken for valid channels any more ; the old
  
  code had to initialize the channels to -1 to solve this problem and had
  
  to check for whether a channel is set before the retransformation
  
  (because 1 << -1 is UB).
  The only downside of this approach is that the size of the context
  
  increases (by 256 bytes) ; but this is not exceedingly much.
  Finally, the array has been moved to the end of the context ; it is only
  
  used a few times during the initialization process and moving it
  
  decreased the offsets of lots of other entries, reducing codesize.
  Reviewed-by : Paul B Mahol <onemda@gmail.com>
  
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavfilter/af_headphone.c