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• How to get an accurate duration of any audio file quickly ?

  27 septembre 2023, par Steve M

  There are many audio files in the wild encoded with VBR which don't have an accurate duration tag, and command line FFMpeg would output the following :

  



  


  Estimating duration from bitrate, this may be inaccurate

  


  



  (and indeed, it is)

  



  Using libav, we can see that this is tested with the has_duration() function from libavformat/utils.c

  



  I have an audio player that needs to get an accurate duration information using libav. I've tried completely decoding the file and counting the total number of samples decoded which is the usual recommendation (and is accurate), but this can take 10+ seconds on a 60 minute audio file, which is not acceptable.

  



  I notice that there are some closed source audio decoders and music playing apps which can get an accurate duration for these files immediately. There must be some cheap way of determining the accurate duration ? Perhaps a snippet or high-level description would help me out.

  


• Convert file with any extension to MP4 with ffmpeg

  15 novembre 2019, par not legit

  I am using youtube-dl and ffmpeg to create a youtube downloader and converter (for personal use). I am trying to download a video and convert it to MP4.

  The problem I have, is that youtube-dl downloads the video in a variety of formats. Is there a way that I can download the video and then tell FFMPEG to convert it, not knowing the current file type ?

  I tried using a * wild card but that results in an error.

  @echo off
  
  title youtube downloader
  
  
  
  set /p name= URL: 
  
  echo Select a type. (vid/mp3/mp4)
  
  set /p type=
  
  
  
  IF /i "%type%"=="vid" goto vid
  
  IF /i "%type%"=="mp3" goto mp3
  
  IF /i "%type%"=="mp4" goto mp4
  
  
  
  :vid
  
  youtube-dl %name%
  
  goto commonexit
  
  
  
  :mp3
  
  youtube-dl -x --audio-format mp3 %name%
  
  goto commonexit
  
  
  
  :mp4
  
  youtube-dl -o video %name%
  
  ffmpeg -i video.* video.mp4 -hide_banner
  
  
  
  :commonexit
  
  pause

• ffmpeg itsoffset doesnt apply offset to mp4

  26 juillet 2019, par brux

  The following command mixes an mp4 and an mp3 together, keeping the audio from the mp4.

  ffmpeg -i video.mp4 -i audio.mp3 -map 0:v -c:v copy -filter_complex '[0:a][1:a]amix[aout]' -map '[aout]' -shortest out.mp4

  The command works as expected.

  Now I want to offset the mp4 file (both the audio and video stream of the mp4) so that there is a delay of 500ms at the start of the mp4, here is my command :

  ffmpeg -itsoffset 00:00:00.500 -i video.mp4 -i audio.mp3 -map 0:v -c:v copy -filter_complex '[0:a][1:a]amix[aout]' -map '[aout]' -shortest out.mp4

  This doesnt work as expected, the output doesnt have the expected delay of 500ms at the start of the mp4 streams. It appears the output is just the same as the first command I ran.

  The version of ffmpeg I am using is :

  ffmpeg version n4.0-39-gda39990

  Here are the files I’m using :

  video.mp4

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/storage/emulated/0/video.mp4':
  
        Metadata:
  
          major_brand     : mp42
  
          minor_version   : 0
  
          compatible_brands: isommp42
  
          creation_time   : 2019-07-26T03:28:49.000000Z
  
          com.android.version: 8.0.0
  
        Duration: 00:00:07.64, start: 0.000000, bitrate: 20534 kb/s
  
          Stream #0:0(eng): Video: h264 (avc1 / 0x31637661), yuvj420p(pc, smpte170m), 1920x1080, 20966 kb/s, SAR 1:1 DAR 16:9, 29.70 fps, 29.75 tbr, 90k tbn, 180k tbc (default)
  
          Metadata:
  
            rotate          : 270
  
            creation_time   : 2019-07-26T03:28:49.000000Z
  
            handler_name    : VideoHandle
  
          Side data:
  
            displaymatrix: rotation of 90.00 degrees
  
          Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 96 kb/s (default)
  
          Metadata:
  
            creation_time   : 2019-07-26T03:28:49.000000Z
  
            handler_name    : SoundHandle

  audio.mp3

  Input #0, mp3, from '/storage/emulated/0/audio.mp3':
  
        Metadata:
  
          album           : Sunflower (Spider-Man: Into the Spider-Verse) - Single
  
          composer        : Louis Bell, Carter Lang, Austin Richard Post, Billy Walsh & Khalif Malik Ibin Shaman Brown
  
          genre           : Hip-Hop/Rap
  
          copyright       : This Compilation ℗ 2018 Republic Records, a division of UMG Recordings, Inc.
  
          title           : Sunflower (Spider-Man: Into the Spider-Verse)
  
          artist          : Post Malone & Swae Lee
  
          album_artist    : Post Malone & Swae Lee
  
          track           : 01/01
  
          TYER            : 2018-10-18T07:00:00Z
  
        Duration: 00:02:38.07, start: 0.000000, bitrate: 325 kb/s
  
          Stream #0:0: Audio: mp3, 44100 Hz, stereo, fltp, 320 kb/s
  
          Stream #0:1: Video: mjpeg, yuvj444p(pc, bt470bg/unknown/unknown), 1400x1400 [SAR 300:300 DAR 1:1], 90k tbr, 90k tbn, 90k tbc
  
          Metadata:
  
            comment         : Cover (front)