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• ffmpeg clip audio interval with starting and end time

  27 novembre 2018, par Raymond Huang

  I am trying to clip an MP3 between two starting points, like starting at 10 seconds and ending at 16 seconds (time interval of 6 seconds).

  I am using this command :

  ffmpeg -ss 10 -i input.mp3 -t 6 output.mp3

  The resulting output.mp3 contains the 6 seconds that I specified followed by 8 or 9 seconds of empty audio. Is there something wrong with my command ?

  Edit :

  ffmpeg -ss 10 -t 6 -i input.mp3 output.mp3 says -t is not an input option, keeping it for the next output; consider fixing your command line. and gives me a file that’s got 8 seconds of audio starting from 10s and then some 9 or 10 seconds of silence.

  ffmpeg -ss 10 -to 16 -i input.mp3 output.mp3 produces a file that is twice the length of the original - basically the same audio file repeated again.

  Testing the output :

  I used Quicktime and it has silent audio at the end. The description of the output file in finder says like 14 seconds. When I use VLC, it plays for the correct 6 seconds and stops, even though its duration in the file browser in VLC says 14. My MPlayer doesn’t work properly. I also did the preview audio in Finder, and it plays the 6 seconds properly and then stops. But the round seeker bar of the MP3 didn’t reach the end. And it also says 14 seconds instead of 6.

  My goal is to stream this 6 second file through a REST API to the front end. I want the user to be able to download this file properly. Ideally it won’t have inconsistent metadata (14 seconds instead of 6).

• starting ffmpeg on an explicit frame

  15 février 2018, par resatee

  I am trying to slica a file. I want the first part to end after 1550 frames and the second one to go from frame 1551 to 3000. The first part wasn’t a problem, I used that line :

  ffmpeg.exe -i foo.hevc -c copy -frames:v 1549 -s 1920x1080 foo_1sthalf.hevc

  For the second part I tried this :

  ffmpeg.exe -ss 30 -i foo.hevc -c copy -s 1920x1080 foo_2ndhalf.hevc

  and this :

  ffmpeg.exe -ss 00:00:30 -i foo.hevc -c copy -s 1920x1080 foo_2ndhalf.hevc

  and this :

  ffmpeg.exe -start_number 1550 -i foo.hevc -c copy -s 1920x1080 foo_2ndhalf.hevc

  but nothing worked.
  Error message is always :

  could not seek to position 30.000

  Do you know a way to start at a certain frame ?
  I have ffmpeg version 3.2

• FFMPEG low bitrate at starting frames

  21 janvier 2018, par Y. T

  So I noticed that the first 1-4s of the videos that I’m converting start with a low bitrate and gradually increase untill its around the specified bitrate (-crf 17 -minrate 2000k -maxrate 3000k -bufsize 2000k).

  ...
  
  frame= 37 fps= 0.0 q=24.0 size = 113kB time=00:00:02.08 bitrate= 443.5kbits/s
  
  frame= 66 fps= 64 q=30.0 size = 619kB time=00:00:03.20 bitrate= 1581.6kbits/s
  
  frame= 99 fps= 64 q=28.0 size = 1106kB time=00:00:04.52 bitrate= 2002.2kbits/s
  
  frame= 131 fps= 63 q=23.0 size = 1599kB time=00:00:05.82 bitrate= 2247.8kbits/s
  
  ...

  I already tried changing several settings like -crf, -b:v, -minrate, -maxrate and -bufsize. From my trial-and-error experience, the lower the -crf / higher -b:v, the faster it reaches an appropriate bitrate, but it still has this "lagg" in the beginning of the conversion.

  Is it possible to immediately start with, for example 2000kbits/s, at the start of the conversion ?

  EDIT

  Around the first 1-30s (roughly), the clips are more pixelated than the rest of the clip. See this image for a comparison (zoomed in on area of an 1080p clip). The rest of the clip doesn’t have any visible loss like this (1850kbps encoded vs 2000kbps original), so I still assume it has something to do with the start of the encoding.