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• ffmpeg copy a part of a video wrt to milliseconds accurately

  25 août 2016, par Santhosh Yedidi

  I am using ffmpeg to copy a part of video.

  I am using mpv to view the video. I get the start time and end time from it.

  ffmpeg -i "main.flv" -ss 01:54:34.340 -to 02:01:13.073 -c copy copied.mp4

  the problem i am facing is the video does not start from 01:54:34.340, it starts from 01:54:34.608

  so its shifting the start poistion.

  Is there any way i can start from the exact millisecond position or form that particular frame.

  or is there command to mention start frame number and end frame number. For that mpv also should tell me the frame numbers in ths OSD

  the output of the above command is

  Input #0, flv, from 'main.flv':
  
    Metadata:
  
      author          : 
  
      copyright       : 
  
      description     : 
  
      keywords        : 
  
      rating          : 
  
      title           : 
  
      presetname      : Custom
  
      creationdate    : Thu Aug 25 04:50:55 2016
  
                      : 
  
      videodevice     : VidBlaster
  
      avclevel        : 31
  
      avcprofile      : 77
  
      videokeyframe_frequency: 5
  
      audiodevice     : Realtek HD Audio Input
  
      audiochannels   : 2
  
      audioinputvolume: 100
  
    Duration: 03:55:58.86, start: 0.033000, bitrate: 855 kb/s
  
      Stream #0:0: Video: h264 (Main), yuv420p(tv), 640x480 [SAR 1:1 DAR 4:3], 819 kb/s, 30.30 fps, 29.97 tbr, 1k tbn, 59.94 tbc
  
      Stream #0:1: Audio: aac (LC), 22050 Hz, stereo, fltp, 49 kb/s
  
  Output #0, mp4, to 'copied.mp4':
  
    Metadata:
  
      author          : 
  
      copyright       : 
  
      description     : 
  
      keywords        : 
  
      rating          : 
  
      title           : 
  
      presetname      : Custom
  
      creationdate    : Thu Aug 25 04:50:55 2016
  
                      : 
  
      videodevice     : VidBlaster
  
      avclevel        : 31
  
      avcprofile      : 77
  
      videokeyframe_frequency: 5
  
      audiodevice     : Realtek HD Audio Input
  
      audiochannels   : 2
  
      audioinputvolume: 100
  
      encoder         : Lavf57.25.100
  
      Stream #0:0: Video: h264 ([33][0][0][0] / 0x0021), yuv420p, 640x480 [SAR 1:1 DAR 4:3], q=2-31, 819 kb/s, 30.30 fps, 29.97 tbr, 16k tbn, 1k tbc
  
      Stream #0:1: Audio: aac (LC) ([64][0][0][0] / 0x0040), 22050 Hz, stereo, 49 kb/s
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (copy)
  
    Stream #0:1 -> #0:1 (copy)
  
  Press [q] to stop, [?] for help
  
  frame=    0 fps=0.0 q=-1.0 size=       0kB time=00:00:00.00 bitrate=N/A speed=  frame=    0 fps=0.0 q=-1.0 size=       0kB time=00:00:00.00 bitrate=N/A speed=  frame=11906 fps=8002 q=-1.0 Lsize=   41574kB time=00:06:38.75 bitrate= 854.1kbits/s speed= 268x    
  
  video:38866kB audio:2336kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.904480%

• Error using FFMPEG to create videos from a list of images

  3 août 2016, par user2308191

  I have a text file that contains the path of some images(the images are in order in the text file), the file looks like this :

  /home/Recording-Session-1456734351095_images/output_0001.png
  
  /home/Recording-Session-1456734351095_images/output_0002.png
  
  /home/annotations/rec_1456734351095/annotated_output_0003.png
  
  .......

  I want to use ffmpeg to create a video from these images. Here is the command I am using :

  ffmpeg -framerate 20 -f image2 -i images.txt -c:v libx264 -r 20 -pix_fmt yuv420p out.mp4

  but it gives me this error :

  [image2 @ 0x32ce7a0] Could not find codec parameters for stream 0 (Video: none, none): unknown codec
  
  Consider increasing the value for the 'analyzeduration' and 'probesize' options

  I tried different numbers for analyzeduration and probesize, but the error still exists, any idea what is the problem ?

• ffmpeg audio and video out of sync when using the raw format

  29 juillet 2016, par Mikhail Novikov

  I have 2 .webm files, one contains video, the other one audio. I need to produce a single mp4 file containing both video and audio, in sync. Here is what i try to do :

  ffmpeg -ss 00:00:00.33 -i user_17624_1-1762.webm -i user_17624_2-1767.webm -r 15 output_good.mp4

  -ss by 0.33s is because video started 0.33s before audio - 1762 and 1767 are frame numbers, so they are 5 frames off, and 15 fps.

  Doing this, i get a perfect recording where video and audio are in sync over the entire file.

  But the thing is, i need to do some alterations of the video frames, and i do it my a C app manipulating the bytes in a raw video stream, so i can’t do it this way, i need to transcode to RAW first, then manipulate, then encode mp4 back from the raw. Removing my C app from the chain to make sure it’s not the problem, it boils down to :

  ffmpeg -ss 00:00:00.33 -i user_17624_1-1762.webm -an -r 15 -f rawvideo -pix_fmt yuv420p -s 1920x1080 ./video.pipe &
  
  ffmpeg -i user_17624_2-1767.webm -vn -ar 44100 -ac 2 -f s16le -acodec pcm_s16le ./audio.pipe &
  
  ffmpeg -an -r 15 -f rawvideo -pix_fmt yuv420p -s 1920x1080 -i ./video.pipe -vn -ar 44100 -ac 2 -f s16le -acodec pcm_s16le -i ./audio.pipe -r 15 output_bad.mp4

  resulting in yes, recording where audio and video are way off from each other, and seems to be also fluctuate over the file duration.

  What am i doing wrong with these video transcodings ? Help me please :)

  Mikhail