[FFmpeg-trac] #8559(undetermined:new): Windows: EBU R128 filter lag when capturing from sound card

FFmpeg trac at avcodec.org
Sun Mar 8 00:04:52 EET 2020


#8559: Windows: EBU R128 filter lag when capturing from sound card
-------------------------------------+-------------------------------------
             Reporter:               |                     Type:  defect
  chrisdoernen                       |
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:  git-
  undetermined                       |  master
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 == Summary of the bug: ==
 When capturing from a sound card on windows, the EBU R128 filter does not
 print it's metadata continuously as it is calculated (every 100ms) but
 rather in "chunks" every 500ms or so. This does not happen when specifying
 a mp3 file with the realtime flag (-re). Please see the corresponding
 commands below.

 On Ubuntu, both variations (capturing from sound card and file) produce
 the same continuous output. Also, live streaming the mp3 encoded audio
 works fine (the commands below are shortened for the purpose of
 demonstration). So I think it is not a problem with my sound card/sound
 system.


 == How to reproduce: ==

 Compare the output over time of this command
 {{{
 ffmpeg.exe -re -i test.mp3 -filter_complex
 ebur128=metadata=1,ametadata=print:key=lavfi.r128.M:file=-:direct=1 -f
 null -
 }}}

 with the output over time of the following command (adapting the input
 parameter)
 {{{
 ffmpeg.exe -y -f dshow -i audio="Mikrofonarray (Realtek High Definition
 Audio)" -filter_complex
 ebur128=metadata=1,ametadata=print:key=lavfi.r128.M:file=-:direct=1 -f
 null -
 }}}

 Observe that the output of the first command is printed smootly, one frame
 at a time, the output of the second command gives multiple frames at once.


 == Ffmpeg version: ==
 20200306-cfd9a65 (Windows Build from Zeranoe, Static linked, 64bit)


 Background info about the use case:
 I am building an audio streaming application where I want to display the
 momentary loudness in real time as a volume meter.

--
Ticket URL: <https://trac.ffmpeg.org/ticket/8559>
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