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• Converting HLS video with fmp4 segments to image thumbnails via ffmpeg with start offset using fast seek

  19 octobre 2022, par hellerahum

  I'm having trouble with what I think should be a basic use case for ffmpeg. What I'd like to do is take an hls video in fmp4 and output 30s of images at 10fps, using "fast seek" to start at an offset well into the video. This works with an Apple sample using ts segments, but not with fmp4 segments.

  


  working sample (ts)

  


  ffmpeg -ss 00:00:05 -i https://devimages.apple.com.edgekey.net/iphone/samples/bipbop/bipbopall.m3u8 -t 30 -vf fps=10 hls_samples/img%03d.jpg


  


  broken sample (fmp4)

  


  ffmpeg -ss 00:00:05 -i https://devstreaming-cdn.apple.com/videos/streaming/examples/img_bipbop_adv_example_fmp4/master.m3u8 -t 30 -vf fps=10 hls_samples/img%03d.jpg


  


  The broken sample spits out errors like :

  


  [NULL @ 0x123e30d20] Invalid NAL unit size (-2003396084 > 1673).
[NULL @ 0x123e30d20] missing picture in access unit with size 1677


  


  and then finally :

  


  Output file is empty, nothing was encoded (check -ss / -t / -frames parameters if used)
Conversion failed!


  


  When I re-encode the fmp4 video adding keyframes via -g 1 (still hls with fmp4) I'm then able to use the fast seek -ss flag before the -i , but i'd rather not do this in a 2-step process, and ideally would take the original hls/fmp4 manifest and output the thumbnails directly. Both samples work with the -ss flag after the input (slow seek) but I have some long (10+ hour) videos so that's not tenable. Anyone able to point me to what I'm doing wrong, or is it possible this is an issue with ffmpeg and its support for fmp4 ? I'm using ffmpeg v5.1.2 and have checked on both an M1 mac and Ubuntu system.

  


• FFmpeg - selecting appropriate bitrate for VP9 encoding

  6 avril 2017, par fastily

  I am looking to encode a 4k video shot with iPhone 6s in VP9 in the best quality possible.

  For reference, stream data of the video I would like to encode, via ffprobe :

  Duration: 00:00:10.48, start: 0.000000, bitrate: 46047 kb/s
  
      Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 3840x2160, 45959 kb/s, 29.98 fps, 29.97 tbr, 600 tbn, 1200 tbc (default)
  
      Metadata:
  
        creation_time   : 2017-03-13T21:12:56.000000Z
  
        handler_name    : Core Media Data Handler
  
        encoder         : H.264
  
      Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 79 kb/s (default)
  
      Metadata:
  
        creation_time   : 2017-03-13T21:12:56.000000Z
  
        handler_name    : Core Media Data Handler

  I am using the following FFmpeg commands, based on these instructions (see Best Quality (Slowest) Recommended Settings section).

  1. ffmpeg -i INPUT.mov -c:v libvpx-vp9 -pass 1 -b:v 46000K -threads 4 -speed 4 -g 9999 -an -f webm -y /dev/null
  2. ffmpeg -I INPUT.mov -c:v libvpx-vp9 -pass 2 -b:v 46000K -threads 4 -speed 0 -g 9999 -an -f webm OUTPUT.webm

  Is there a best practice to select an optimal -b:v value such that the resulting video is visually indistinguishable from the original ? I have tried values ranging from 36000K-46000K, but these result in massive files with an overall bitrate exceeding the target bitrate.

  Thanks in advance !

• FFmpeg - selecting appropriate bitrate for VP9 encoding

  11 janvier 2018, par fastily

  I am looking to encode a 4k video shot with iPhone 6s in VP9 in the best quality possible.

  For reference, stream data of the video I would like to encode, via ffprobe :

  Duration: 00:00:10.48, start: 0.000000, bitrate: 46047 kb/s
  
      Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 3840x2160, 45959 kb/s, 29.98 fps, 29.97 tbr, 600 tbn, 1200 tbc (default)
  
      Metadata:
  
        creation_time   : 2017-03-13T21:12:56.000000Z
  
        handler_name    : Core Media Data Handler
  
        encoder         : H.264
  
      Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 79 kb/s (default)
  
      Metadata:
  
        creation_time   : 2017-03-13T21:12:56.000000Z
  
        handler_name    : Core Media Data Handler

  I am using the following FFmpeg commands, based on these instructions (see Best Quality (Slowest) Recommended Settings section).

  1. ffmpeg -i INPUT.mov -c:v libvpx-vp9 -pass 1 -b:v 46000K -threads 4 -speed 4 -g 9999 -an -f webm -y /dev/null
  2. ffmpeg -I INPUT.mov -c:v libvpx-vp9 -pass 2 -b:v 46000K -threads 4 -speed 0 -g 9999 -an -f webm OUTPUT.webm

  Is there a best practice to select an optimal -b:v value such that the resulting video is visually indistinguishable from the original ? I have tried values ranging from 36000K-46000K, but these result in massive files with an overall bitrate exceeding the target bitrate.

  Thanks in advance !