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• FFmpeg - Change resolution of the video with aspect ratio

  10 août 2016, par Arthur Khusnutdinov

  all.

  How to change resolution of the video with aspect ratio with FFmpeg ?

  There are options
  http://manpages.ubuntu.com/manpages/oneiric/man1/ffmpeg.1.html

         -s size
  
         Set frame size. The format is wxh (ffserver default = 160x128,
  
         ffmpeg default = same as source).  The following abbreviations are
  
         recognized:

  and

         -aspect aspect
  
         Set the video display aspect ratio specified by aspect.
  
  
  
         aspect can be a floating point number string, or a string of the
  
         form num:den, where num and den are the numerator and denominator
  
         of the aspect ratio. For example "4:3", "16:9", "1.3333", and
  
         "1.7777" are valid argument values.

  For example, I have two input videos :

  • with 200*400 resolution
  • with 400*700 resolution

  I need to make output video with 100*200 resolution.

  If I will run ffmpeg with -s 100x200, then second video will have bad aspect ratio.

  How can I limit output video by width, with auto aspect ratio by height ?

  For example, I want specify for the output video only width 100px and ffmpeg must automatically calculate height with right aspect ratio.

  For first video it will be :

  200/100=2

  400/2=200

  Ie 100x200

  For second video it will be :

  400/100=4

  700/4=75

  Ie 100x75

  Is it possible ?

• ffprobe : Check for invalid matrix error when printing rotation

  22 septembre 2022, par Derek Buitenhuis

  ffprobe : Check for invalid matrix error when printing rotation
  av_display_rotation_get will return NAN when the display matrix is invalid,
  
  which would end up printing NAN as an integer in the rotation field. This
  
  is poor for multiple reasons :
  * Users of ffprobe have no way of discerning "valid but ugly rotation from
  
    display matrix" from "invalid display matrix".
  
  * It can have unintended consequences on some platforms, such as Linux x86_64,
  
    where NAN is equal to INT64_MIN, which, for example, when printed as JSON,
  
    which uses floating point for all numbers, can end up as invalid JSON or wit
  
    a number that cannot be reserialized as an integer at all.
  Since NAN is av_display_rotation_get's error case, just print 0 (no rotation)
  
  when that happens.
  Signed-off-by : Derek Buitenhuis <derek.buitenhuis@gmail.com>
  

  • [DH] fftools/ffprobe.c

• Seeking Guidance on Audio Development Libraries for Playing Various Music Formats on iOS [closed]

  3 décembre 2023, par FaiChou

  I am exploring audio development and am overwhelmed by the numerous libraries available :

  


  

  • AVFoundation

  


  • MediaPlayer

  


  • AVFAudio

  


  • Audio Engine

  


  • CoreAudio

  


  • AudioToolbox

  


  • Audio Unit

  


  


  Which of these should I use to play both network or local music files (flac/wav/mp3/aac/wma/ogg) ? What are their specific roles ?

  


  My understanding is that I should use ffmpeg for demuxing to unpackage, then decode the stream to get PCM samples, possibly using Audio Engine for playback. Is this a software decoding method ? For Apple-supported formats like mp3, can I bypass ffmpeg for decoding ? Which library would be most suitable in this case ?

  


  Additionally, how do I extract metadata (song name, artist, cover, lyrics, etc.) from music files ? Apple's own solutions seem to support only ID3 or iTunes tags. How should I handle other formats like wav/flac ?

  


  The two links below are the resources I've referenced, but they seem outdated. My search for newer, reliable explanations has been fruitless.

  


  

  • whats-the-difference-between-the-apple-audio-frameworks

  


  • Core Audio Essentials