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• How to mix multiple audios from the end ?

  24 avril 2020, par Vijay Singh Kholiya

  In my project I have a feature of recording the meeting which is in a form of group discussion consisting of multiple attendees. All attendees will be having their own personal system and they will be accessing that web app through their personal account. Their is one meeting controller(only one person) who starts the recording and for every attendee whether he is present in the same room or is remote, their microphone will be opened and recording will be stored in S3 bucket.

  



  Since I need a single audio file which consists of the whole meeting recording, so I am using SOX for this. But the problem is, what if any attendee attends meeting in between the discussion so he's audio recording length will be smaller than everyone else.

  



  Since I am mixing the audio files to get one file, but for this late commer attendee the mixing will be wrong. So how can I mix the audios from the end instead of starting ?

  


• Standardized "Skip Intro" in MP4 video files ?

  25 mai 2020, par Crissov

  Is there a standardized way to mark up specific parts of a MP4-contained video as skippable, e.g. trailers, recaps, intros/outros, opening/closing credits, in the metadata in the file itself ? If possible, I would like to set this with FFmpeg or MP4box.

  



  I know that the mvhd box in MOV files makes it possible to specify a single preview. 
I assume Netflix and the like use specially named or hinted chapters, either from file-internal metadata or from a central database, to provide this feature. 
I want to add this now to videos in my personal library, just in case Kodi, VLC or other players and media centers add support for this feature.

  



  Edit List Box elst

  



  As mentioned in the first comment, Edit Lists may be a solution. They are specified in section 8.6.6 of ISO/IEC 14496-12:2015 (ISOBMFF), which I partially cite below.

  



  moov > trak+ > edts ? > elst*

  



  


  [elst] contains an explicit time-line map. 
 Each entry defines part of the track time-line :
  
 by mapping part of the media time-line,
  
 or by indicating ‘empty’ time,
  
 or by defining a ‘dwell’, where a single time-point in the media is held for a period.

  
 


  

  • version is an integer that specifies the version of this box (0 or 1)

  


  • entry_count is an integer that gives the number of entries in the following table

  


  • segment_duration is an integer that specifies the duration of this edit segment in units of the timescale in the Movie Header Box

  


  • media_time is an integer containing the starting time within the media of this edit segment (in media time scale units, in composition time). If this field is set to –1, it is an empty edit. The last edit in a track shall never be an empty edit. Any difference between the duration in the Movie Header Box, and the track’s duration is expressed as an implicit empty edit at the end.

  


  • media_rate specifies the relative rate at which to play the media corresponding to this edit segment. If this value is 0, then the edit is specifying a ‘dwell’ : the media at media-time is presented for the segment-duration. Otherwise this field shall contain the value 1.

  


  


  


• Building FFmpeg for use in Swift

  7 juillet 2021, par NCrusher

  With the new XCode/Swift release comes the ability to use binary dependencies. This seems to me to be an ideal time to create an SPM package for FFMpeg.

  


  However, while I've spent the last year learning to code i Swift, I'm actually not all that familiar with how to build libraries, especially those as complex as FFmpeg with all the configurable libraries and third-party dependencies.

  


  There's kewlbear's iOS build scripts, but these are for iOS/tvOS and ideally an FFMpeg SPM package would be usable for MacOS also. It's also not updated for the newest Xcode and Swift versions.

  


  My personal interest is simply in audio and I don't need a lot of bells and whistles, but I figure the ideal situation would be a full package with the entire source and whatever dependencies it needs, and then when it's used as a package dependency, the compiler will just use the parts it needs.

  


  I guess my question is...how would I ideally compile the ffmpeg code for this purpose. I'm trying to follow the directions for compiling yourself, but I'm stuck at the point of compiling gettext because I'm not sure if I should follow the directions (in the gettext source code) for compiling a fat binary for multiple architectures, and when I try to run :

  


        ./configure CC="gcc -arch i386 -arch x86_64 -arch ppc -arch ppc64" \
                  CXX="g++ -arch i386 -arch x86_64 -arch ppc -arch ppc64" \
                  CPP="gcc -E" CXXCPP="g++ -E"



  


  I get the following error :

  


   checking whether the C compiler works... no configure: error: in
 `/Users/nolainecrusher/Downloads/FFMpeg-source/gettext-0.21/gettext-runtime':
 configure: error: C compiler cannot create executables See
 `config.log' for more details configure: error: ./configure failed for
 gettext-runtime


  


  and config.log doesn't really tell me anything useful :

  


  This is what I see at the end of the log :

  


   mkdir_p='$(MKDIR_P)' oldincludedir='/usr/include' pdfdir='${docdir}'
 prefix='/usr/local' program_transform_name='s,x,x,' psdir='${docdir}'
 sbindir='${exec_prefix}/sbin' sharedstatedir='${prefix}/com' subdirs='
 gettext-runtime libtextstyle gettext-tools' sysconfdir='${prefix}/etc'
 target_alias=''


  


  I feel like maybe I'm going about this the wrong way, but I'm not sure what the right way is.