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• How to save ffmpeg segmets to disk immediately with sub-second intervals ?

  20 octobre 2023, par amfast

  I'm trying to record video on a raspberry and have it save as much as possible (sub-second resolution) in case of a power cutoff.

  


  I use -f segment to save the encoded stream in 100ms segments with the hope that all but the interrupted (by power cutoff) segment will be saved in memory. Unfortunately, when cutting off power, all the destination files (output_0001.mp4, output_0002.mp4, ...) are created, but empty.

  


  To save the files to disk immediately, I added the -strftime 1 option that allows formatting the output filename as time. It seems weird that this is the (only ?) way to trigger immediate saving of files, but it works - untill I try to have segments smaller than 1 second. The problem seems to be that the format string %d, that previously added a sequence number in my output filenames, now represents "day" (i.e. date) and the smallest resolution time format string is %S for second. I saw %f suggested somewhere for smaller resolutions, but it only prints "%f".

  


  The result is that the segmentation part of ffmpeg does create 100ms segments and save them to disk immediately, but the strftime feature gives the output files names that only change every second, so all the interim files are overwritten.

  


  Example of the failing command below. Without the -strftime option this creates nice segments, but does not save them to disk immediately.

  


  libcamera-vid --flush \
    --framerate ${FRAMERATE} \
    --width ${WIDTH} \
    --height ${HEIGHT} \
    -n \
    -t ${TIMEOUT} \
    --codec yuv420 \
    -o - | 
ffmpeg \
    -fflags nobuffer \
    -strict experimental \
    -loglevel debug \
    -flags low_delay \
    -f rawvideo \
    -pix_fmt yuv420p \
    -s:v ${WIDTH}x${HEIGHT} \
    -r ${FRAMERATE} \
    -i - \
    -c:v h264_v4l2m2m \
    -f segment \
    -segment_time 0.1 \
    -segment_format mp4 \
    -reset_timestamps 1 \
    -strftime 1 \
    -b:v ${ENCODING_BITRATE} \
    -g 1 \
    "output_%04d.mp4"


  


  Question :
  
Is there another way besides -strftime to trigger immediate saving ? Or is there a mechanism to feed finer resolution format strings to the output filename ?

  


• Node package 'videoshow' ffmpeg error

  14 octobre 2015, par Jon Stevens

  I am using the npm library ’videoshow’ to build a video slideshow with images and audio. I have copied everything directly from the github wiki as far as installing the package and configuring ffmpeg to include the necessary flags. My code for the main ’generation.js’ node file :

  var videoshow = require('videoshow');
  
  
  
  var images = [
  
    '2.jpg',
  
    '4.jpg'
  
  ]
  
  
  
  var videoOptions = {
  
    fps: 25,
  
    loop: 5, // seconds
  
    transition: true,
  
    transitionDuration: 1, // seconds
  
    videoBitrate: 1024,
  
    videoCodec: 'libx264',
  
    size: '640x?',
  
    audioBitrate: '128k',
  
    audioChannels: 2,
  
    format: 'mp4'
  
  }
  
  
  
  videoshow(images, videoOptions)
  
    .audio('song.mp3')
  
    .save('video.mp4')
  
    .on('start', function (command) {
  
      console.log('ffmpeg process started:', command)
  
    })
  
    .on('error', function (err, stdout, stderr) {
  
      console.error('Error:', err)
  
      console.error('ffmpeg stderr:', stderr)
  
    })
  
    .on('end', function (output) {
  
      console.error('Video created in:', output)
  
    })

  Just running the above code with ’node generation.js’ which is the default usage and the exact settings they explain in the wiki is giving the error :

  ffmpeg process started : ffmpeg -i /tmp/videoshow-3fe871bc-e082-4ed8-bf47-f10c854f1718 -i /tmp/videoshow-a1595d76-dcbd-48c3-a8b3-cffac6951ed3 -y -filter_complex concat=n=2:v=1:a=0 video.mp4
  ffmpeg process started : ffmpeg -i /tmp/videoshow-7b78fd53-408f-40a8-8974-665f18f1fe41 -i song.mp3 -y -b:a 128k -ac 2 -r 25 -b:v 1024k -vcodec libx264 -filter:v scale=w=640:h=trunc(ow/a/2)*2 -f mp4 -map 0:0 -map 1:0 -t 10 -af afade=t=in:ss=0:st=0:d=3 -af afade=t=out:st=7:d=3 video.mp4
  Error : [Error : ffmpeg exited with code 1 : ]
  ffmpeg stderr : undefined

  If anyone has any experience at all with this library, any help is greatly appreciated !

• Music Video Idiosyncrasies

  18 juin 2011, par Multimedia Mike — General

  So I’m watching a fairly recent music video for a song named "XXXO" from an artist named M.I.A. when I’m suddenly assaulted by this imagery :

  
  
  

  ... and I enter nervous convulsions. You see, while this might seem to be an odd video effect to the casual viewer, to a multimedia hacker, it appears to be deliberately antagonistic. To anyone who has written a video codec, this scene looks like an entire casserole of video bugs, combining creeping plane offsets errors, chroma problems, and interlacing havoc. The craziest part is to realize that this is probably some kind of standard video effect / filter type. Upon a repeat viewing, I realized that the entire video sort of looks like an amateur video editor’s first week using video software.

  Elsewhere in the video, a YouTube-style video frame vortex highlights the proceedings. I guess I need to come to terms with the fact that the ubiquitous player frame is just part of the digital Zeitgeist now :

  
  
  

  Vintage Video Strangeness
  I’m a long-time music video junkie but I have a tendency of examining them entirely too closely. I first saw Paula Abdul’s video for "Cold-Hearted" when I was just starting to understand multimedia technology and how it interacted with emerging home computers. Imagine how confused I was when I tried to make sense of the actions performed by our eMaestro "Chuck" whom Paula has instructed to "hit it". First, he hits a key followed by 3 quick strikes on a second key :

  
  
  

  Then, the "start music" action is apparently bound to a particular key on the electronic keyboard :
  
  

  
  
  

  Which kicks off the electronic metronome on the computer. Each identical-sounding beat quizzically maps to a different frequency transform :

  
  
  a one...
  
  and a two...
  
  and a three...
  

  I had no trouble believing things up to this point. But even though I didn’t understand what was going on with that frequency transform, I knew that it must have had something to do with the audio. And if the audio was the same, the visualization ought to be the same. Though, to be fair, I will concede that the first and third ticks pictured bear some mutual resemblance.

  Anyway, the software is probably real even if the keyboard interaction was stylized. Can anyone identify the software ? What about the computer ? This is perhaps the best view the video gives us :

  
  
  

  So, remember, don’t base your understanding of technology — or anything, really — on stylized media representations. Don’t even get me started on the movie "Sneakers." That had me confused about cryptography and computer security for many years.