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• checkasm : use perf API on Linux ARM*

  1er septembre 2017, par Clément Bœsch

  checkasm : use perf API on Linux ARM*
  On ARM platforms, accessing the PMU registers requires special user
  
  access permissions. Since there is no other way to get accurate timers,
  
  the current implementation of timers in FFmpeg rely on these registers.
  
  Unfortunately, enabling user access to these registers on Linux is not
  
  trivial, and generally involve compiling a random and unreliable github
  
  kernel module, or patching somehow your kernel.
  Such module is very unlikely to reach the upstream anytime soon. Quoting
  
  Robin Murphin from ARM :
  > Say you do give userspace direct access to the PMU ; now run two or more
  
  > programs at once that believe they can use the counters for their own
  
  > "minimal-overhead" profiling. Have fun interpreting those results...
  
  >
  
  > And that's not even getting into the implications of scheduling across
  
  > different CPUs, CPUidle, etc. where the PMU state is completely beyond
  
  > userspace's control. In general, the plan to provide userspace with
  
  > something which might happen to just about work in a few corner cases,
  
  > but is meaningless, misleading or downright broken in all others, is to
  
  > never do so.
  As a result, the alternative is to use the Performance Monitoring Linux
  
  API which makes use of these registers internally (assuming the PMU of
  
  your ARM board is supported in the kernel, which is definitely not a
  
  given...).
  While the Linux API is obviously cross platform, it does have a
  
  significant overhead which needs to be taken into account. As a result,
  
  that mode is only weakly enabled on ARM platforms exclusively.
  Note on the non flexibility of the implementation : the timers (native
  
  FFmpeg vs Linux API) are selected at compilation time to prevent the
  
  need of function calls, which would result in a negative impact on the
  
  cycle counters.
  

  • [DH] configure
  • [DH] tests/checkasm/checkasm.c
  • [DH] tests/checkasm/checkasm.h

• FFprobe command in a var in IF statement

  28 octobre 2017, par bdrilling33

  I am trying to set up a batch file (currently testing in CMD prompt) to run when there is a change in the directory. I have a command stored in a variable "test" which tells me what the first audio codec is. if it isn’t aa3 i plan to re encode the audio with ffmpeg. My first issue is that when i try to run a simple if statement with my var, i get an error.

  set test=ffprobe -v error -select_streams a:0 -show_entries stream=codec_name -of default=nokey=1:noprint_wrappers=1 "my movie (2017).mkv"

  when i run %test% it returns what is expected.

  if i run this as :

  if %test% == "ac3" echo true

  i get :

  -v was unexpected at this time.

  my end goal is to have something like this when something is added to the folder (haven’t go the when something changes part yet...probably just run this once a day idk) :

  set test=ffprobe -v error -select_streams a:0 -show_entries stream=codec_name -of default=nokey=1:noprint_wrappers=1 "%f"
  
  
  
  set outpath=S:\Blu Ray\New folder\"%f"
  
  
  
  for %f in (*.mkv) DO
  
      if %test% <> "ac3" (
  
          ffmpeg -i “%f” -vcodec copy -scodec copy -acodec ac3 -b:a 640k “%outpath%";
  
  del "%f";
  
  move "%outpath%" "s:\Blu Ray\")

  any help would be great

  BD

• Encoding video for streaming with multiple subtitle streams in VLC

  7 janvier 2018, par VinGarcia

  I am implementing an offline video streaming service, so our users can have the encrypted videos on their computers and open them only by using our streaming app.

  So what I need is to stream a freshly decrypted video file directly to a local VLC client so I don’t have to save it on disk. A minimum working example would be :

  cat my_video.mp4 | vlc -

  But this only shows the video and audio tracks, no subtitles.

  I want to know if there is a way to encode a video so that this would work with 3 audio tracks and 3 subtitle tracks.
  I would also settle for an answer explaining that it is not possible and why not.

  More details below :

  ---

  I have 3 audio tracks and 3 subtitle tracks and I am using FFMPEG.
  (The original format of the videos is mp4 with an h264 encoding)

  Currently, I am able to make streamable .mp4 files, thanks to this answer, and also to make .ts files that will show the video and the 3 audio options but not the subtitles. The command I am using is this :

  video_name=demo_0101.mp4
  
  sub_name=demo_0101.srt
  
  output=0101.mp4 # Or `.ts`
  
  
  
  ffmpeg\
  
    -i en_raw/$video_name -i pt_raw/$video_name -i es_raw/$video_name\
  
    -i en_subs/$sub_name\
  
    -i pt_subs/$sub_name\
  
    -i es_subs/$sub_name\
  
    -map 2:v\
  
    -map 0:a:0 -map 1:a:0 -map 2:a:0\
  
    -map 3:s -map 4:s -map 5:s\
  
    -c:v libx264 -crf 22\
  
    -movflags faststart\ # (This line is only necessary for .mp4)
  
    -c:a:0 aac -c:a:1 aac -c:a:2 aac\
  
    -c:s:0 mov_text -c:s:1 mov_text -c:s:2 mov_text\
  
    $output

  The problem is : The subtitles are not recognized (don’t show up at all) using the .ts format and when using .mp4 VLC reports an error :

  Unidentified codec :
  VLC could not identify the audio or video codec

  Please note when not streaming the .mp4 version works with all audios and the subtitles, i.e. :

  vlc my_video.mp4

  ---

  In case someone is wondering I plan on selecting the which subtitle and audio to play from command line with the VLC options : --audio-track 1 --sub-track 0

  I hope someone can help me. Thanks in advance.