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• FFmpeg amix-filter always does "volume normalization". How to prevent it and what are the possible drawbacks of it ?

  14 juin 2020, par Chitrang

  There are many questions on this topic link1, link2, and link3. However, I am asking for suggestions on the probable solution and if it has some drawbacks.

  



  Problem Definition : amix-filter always does "volume normalization" and can't be turned off

  



  Reference : Please read comments over here by @Reino. He also had opened a ticket on the FFmpeg forum to explain the situation.

  



  Hacky Solution : amix=inputs=13:dropout_transition=1000,volume=13

  



  Reference : Answered here, and also in the ticket.

  



  Questions :

  



  1) "amix scales each input's volume by 1/n where n = no. of active inputs. This is evaluated for each audio frame. So when an input drops out, the volume of the remaining inputs is scaled by a smaller amount, hence their volumes increase."Refer

  



  For example, if I am merging 10 audio streams then, the 1st audio stream will be scaled by 1/10, 2nd by 1/9, 3rd by 1/8 .. 9th by 1/2 and last 10th by 1. Have I understood this correctly or let me know if I am missing something ?

  



  2) dropout_transition : The transition time, in seconds, for volume renormalization when an input stream ends. The default value is 2 seconds.

  



  dropout_transition means it will SKIP given seconds, right ? So if I set dropout_transition=1000(very large number) then regardless of video length FFmpeg will drop/skip audio transition for provided seconds. Again, please do correct me if I have made wrong assumption.

  



  3) I have tried many other solutions without any luck and now I am relying profoundly on the provided solution. Is there any drawback to the above hacky solution ?

  


• 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.

  


  


  


• Start of video is not labeled as "0" in QuickTime Video from GoPro

  26 mars 2020, par John Terragnoli

  I’m trying to combine four GoPro videos into a single video, and then rotate it 90 degrees. However, the time scales on the bottom of the videos are all wrong. The videos are 17 minutes and 42 second. But the beginning time is labeled as 5:15:20:32 and the ending time is 5:33:01:32. It just looks really weird and I’d like to fix it. After I use ffmpeg to rotate and concatenate the videos, the problem persists. Could it possibly be fixed with Exiftool ?

  ffmpeg -safe 0 -f concat -i list.txt -vcodec copy -acodec copy merged_videos.MP4

  ffmpeg -i input.mov -vf "transpose=1" output.mov

  Here is the exiftool information on one of the videos :

  File Name                       : GOPR3023.MP4
  
  Directory                       : .
  
  File Size                       : 3.7 GB
  
  File Modification Date/Time     : 2018:04:12 14:56:16-05:00
  
  File Access Date/Time           : 2020:03:25 12:17:18-05:00
  
  File Inode Change Date/Time     : 2020:03:25 17:57:04-05:00
  
  File Permissions                : rwxrwxrwx
  
  File Type                       : MP4
  
  File Type Extension             : mp4
  
  MIME Type                       : video/mp4
  
  Major Brand                     : MP4 v1 [ISO 14496-1:ch13]
  
  Minor Version                   : 2013.10.18
  
  Compatible Brands               : mp41
  
  Movie Data Size                 : 4001979951
  
  Movie Data Offset               : 28
  
  Movie Header Version            : 0
  
  Create Date                     : 2018:04:12 14:38:32
  
  Modify Date                     : 2018:04:12 14:38:32
  
  Time Scale                      : 60000
  
  Duration                        : 0:17:42
  
  Preferred Rate                  : 1
  
  Preferred Volume                : 100.00%
  
  Preview Time                    : 0 s
  
  Preview Duration                : 0 s
  
  Poster Time                     : 0 s
  
  Selection Time                  : 0 s
  
  Selection Duration              : 0 s
  
  Current Time                    : 0 s
  
  Next Track ID                   : 6
  
  Firmware Version                : HD5.03.02.51.00
  
  Lens Serial Number              : NAH6092300301117
  
  Camera Serial Number Hash       : 34676f2cdf49b86a1514817a93377bf7
  
  Track Header Version            : 0
  
  Track Create Date               : 2018:04:12 14:38:32
  
  Track Modify Date               : 2018:04:12 14:38:32
  
  Track ID                        : 1
  
  Track Duration                  : 0:17:42
  
  Track Layer                     : 0
  
  Track Volume                    : 0.00%
  
  Image Width                     : 1920
  
  Image Height                    : 1080
  
  Graphics Mode                   : srcCopy
  
  Op Color                        : 0 0 0
  
  Compressor ID                   : avc1
  
  Source Image Width              : 1920
  
  Source Image Height             : 1080
  
  X Resolution                    : 72
  
  Y Resolution                    : 72
  
  Compressor Name                 : GoPro AVC encoder
  
  Bit Depth                       : 24
  
  Color Representation            : nclx 1 1 1
  
  Video Frame Rate                : 59.94
  
  Time Code                       : 3
  
  Balance                         : 0
  
  Audio Format                    : mp4a
  
  Audio Channels                  : 2
  
  Audio Bits Per Sample           : 16
  
  Audio Sample Rate               : 48000
  
  Text Font                       : Unknown (21)
  
  Text Face                       : Plain
  
  Text Size                       : 10
  
  Text Color                      : 0 0 0
  
  Background Color                : 65535 65535 65535
  
  Font Name                       : Helvetica
  
  Other Format                    : tmcd
  
  Warning                         : [minor] The ExtractEmbedded option may find more tags in the movie data
  
  Matrix Structure                : 1 0 0 0 1 0 0 0 1
  
  Media Header Version            : 0
  
  Media Create Date               : 2018:04:12 14:38:32
  
  Media Modify Date               : 2018:04:12 14:38:32
  
  Media Time Scale                : 60000
  
  Media Duration                  : 0:17:42
  
  Handler Class                   : Media Handler
  
  Handler Type                    : NRT Metadata
  
  Handler Description             : GoPro SOS
  
  Gen Media Version               : 0
  
  Gen Flags                       : 0 0 0
  
  Gen Graphics Mode               : srcCopy
  
  Gen Op Color                    : 0 0 0
  
  Gen Balance                     : 0
  
  Meta Format                     : fdsc
  
  Image Size                      : 1920x1080
  
  Megapixels                      : 2.1
  
  Avg Bitrate                     : 30.1 Mbps
  
  Rotation                        : 0

  Part 2
  There is a pretty obvious "stutter" at the 17:42 mark where the two clips are combined. I’ve tried using ffmpeg and iMovie, but both give the same results. The GoPro broke up the event into multiple clips on it’s own so it seems weird that there would be any information missing. Is there any way to get rid of this stutter ?

  Thanks !