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• Get last 30 seconds of HLS stream with FFMPEG

  3 octobre 2022, par aamirnshah

  I have a live HLS stream which has not yet ended. I am trying to extract the last 30 seconds (now minus 30 seconds clip)

  


  I tried

  


  ffmpeg -sseof -30 -i audio.m3u8 -acodec copy -vcodec copy out.mp4

  


  but this does not work since the audio clip has not ended. Any suggestions ?

  


• While transcoding to mpegts ffmpeg creates the first frame after 1.48 seconds delay

  15 mars 2018, par Biraj B Choudhury

  I have transcoded a file to mpegts using the following command

   ./ffmpeg -y -i big_buck_bunny_720p_5mb.mp4  -vcodec libx264  -x264opts "keyint=48:min-keyint=48:no_scenecut" -r 23.976 -c:a copy  -f mpegts test.mpegts

  When I run ffprobe on it -

  ./ffprobe  -i  test.mpegts  -select_streams v -show_frames -of csv

  I see that the first frame starts at 1.48 seconds why is this so ?

  Input #0, mpegts, from 'test.mpegts':
  
    Duration: 00:00:29.61, start: 1.483422, bitrate: 1964 kb/s
  
    Program 1 
  
      Metadata:
  
        service_name    : Service01
  
        service_provider: FFmpeg
  
      Stream #0:0[0x100]: Video: h264 (High) ([27][0][0][0] / 0x001B), yuv420p(progressive), 1280x720 [SAR 1:1 DAR 16:9], 23.98 fps, 23.98 tbr, 90k tbn, 47.95 tbc
  
      Stream #0:1[0x101](und): Audio: aac (LC) ([15][0][0][0] / 0x000F), 48000 Hz, 5.1, fltp, 406 kb/s
  
  frame,video,0,1,133508,1.483422,133508,1.483422,133508,1.483422,3753,0.041700,564,112008,1280,720,yuv420p,1:1,I,0,0,0,0,0
  
  frame,video,0,0,137262,1.525133,137262,1.525133,137262,1.525133,3753,0.041700,125584,1110,1280,720,yuv420p,1:1,B,2,0,0,0,0

  After some research I added "muxdelay 0" to my command

  ./ffmpeg -y -i big_buck_bunny_720p_5mb.mp4  -vcodec libx264  -x264opts "keyint=48:min-keyint=48:no_scenecut" -r 23.976 -c:a copy  -muxdelay 0 -f mpegts test.mpegts

  And now I get the following in ffprobe

  Input #0, mpegts, from 'test.mpegts':
  
    Duration: 00:00:29.61, start: 0.083422, bitrate: 1987 kb/s
  
    Program 1 
  
      Metadata:
  
        service_name    : Service01
  
        service_provider: FFmpeg
  
      Stream #0:0[0x100]: Video: h264 (High) ([27][0][0][0] / 0x001B), yuv420p(progressive), 1280x720 [SAR 1:1 DAR 16:9], 23.98 fps, 23.98 tbr, 90k tbn, 47.95 tbc
  
      Stream #0:1[0x101](und): Audio: aac (LC) ([15][0][0][0] / 0x000F), 48000 Hz, 5.1, fltp, 406 kb/s
  
  frame,video,0,1,7508,0.083422,7508,0.083422,7508,0.083422,3753,0.041700,564,112008,1280,720,yuv420p,1:1,I,0,0,0,0,0
  
  frame,video,0,0,11262,0.125133,11262,0.125133,11262,0.125133,3753,0.041700,125584,1110,1280,720,yuv420p,1:1,B,2,0,0,0,0

  Can anybody help me understand what is this muxdelay that is contributing to 1.4 seconds of delay and what is contributing to the remaining 0.08 seconds of delay.

  The first frame is at 0.000 when the output is mp4 so this is something particular to mpegts.

• Crop MP3 to first 30 seconds

  11 octobre 2020, par Cheekysoft

  Original Question

  



  I want to be able to generate a new (fully valid) MP3 file from an existing MP3 file to be used as a preview — try-before-you-buy style. The new file should only contain the first n seconds of the track.

  



  Now, I know I could just "chop the stream" at n seconds (calculating from the bitrate and header size) when delivering the file, but this is a bit dirty and a real PITA on a VBR track. I'd like to be able to generate a proper MP3 file.

  



  Anyone any ideas ?

  



  Answers

  



  Both mp3split and ffmpeg are both good solutions. I chose ffmpeg as it is commonly installed on linux servers and is also easily available for windows. Here's some more good command line parameters for generating previews with ffmpeg

  



  

  • -t <seconds></seconds> chop after specified number of seconds

  


  • -y force file overwrite

  


  • -ab <bitrate></bitrate> set bitrate e.g. -ab 96k

  


  • -ar <rate hz="hz"></rate> set sampling rate e.g. -ar 22050 for 22.05kHz

  


  • -map_meta_data <outfile>:<infile></infile></outfile> copy track metadata from infile to outfile

  


  



  instead of setting -ab and -ar, you can copy the original track settings, as Tim Farley suggests, with :

  



  

  • -acodec copy