Recherche avancée

Sur d’autres sites (8224)

• Is it possible to generate a keyframe to start a spliced H.264 video segment ?

  3 janvier 2015, par Ethan T

  When segmenting files with ffmpeg, I am currently only able to splice on keyframe boundaries if I don’t want to reencode. This presents issues if I want to control timing down to a specific frame. To my knowledge, you can only start on a keyframe if you’re performing a stream copy. If you want to start on an arbitrary frame, you must reencode.

  However, for codecs that ffmpeg understands (like H.264), it seems like it would be technically possible to replace the desired first frame with a newly created keyframe without reencoding the rest of the video. This would represent a "smart copy" sort of behavior. For example, say my video consists of these frames and types :

  Frame number:  0         1         2         3
  
                 0123456789012345678901234567890123
  
  Frame type:    IppbppbppbppbIppbppbppbppbIppbppbp
  
  Keyframes:     ^            ^            ^

  (I frames are keyframes while p and b frames are not)

  Currently, if I want to remove the first few frames and start on exactly frame 20, I must reencode the entire stream beginning with that input frame. This would cause an undesired degradation in quality. Instead, if I perform a copy, ffmpeg would begin at the most recent keyframe :

  Frame number:  0         1         2         3
  
                 0123456789012345678901234567890123
  
  Frame type:    IppbppbppbppbIppbppbppbppbIppbppbp
  
  Desired start:                     ^
  
  Actual start:               ^

  Why can’t ffmpeg seek to frame 13 (the last complete keyframe prior to the cut point), fully calculate frame 20, and recreate frame 20 as an I frame ? It would then copy the remaining frames as before. Like this :

  Frame number:  0         1         2         3
  
                 0123456789012345678901234567890123
  
  Input type:    IppbppbppbppbIppbppbppbppbIppbppbp
  
  Output type:                       IpbppbIppbppbp

  It seems like this would be a very useful feature for splicing videos without losing quality. Is there any technical barrier (e.g. the H.264 spec or any other common codec) that prevents this approach ?

• Trying to understand the ffmpeg seek cut functionality

  13 février 2020, par user3841429

  I have a video where I would like to cut a part from. The command I use :

  ffmpeg -ss 526.623 -t 347.986 -i 'example.mp4' -c copy -avoid_negative_ts 1 -y res.mp4

  Where expected length is 00:05:47.99. The process log shows the following :

  ...
  
  frame=10582 fps=8258 q=-1.0 Lsize= 1061446kB time=00:05:47.98 bitrate=24987.8kbits/s speed= 272x    
  
  video:1044531kB audio:16556kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.033789%

  As you can see time=00:05:47.98 as expected, but when I play this video in player I see that it has extra 5 seconds of video at the end. I check the playtime length :

  $ ffmpeg -i 'res.mp4' 2>&1 | grep Duration | cut -d ' ' -f 4 | sed s/,//
  
  00:05:53.11

  What the... My clue was the GOP’s I-frame, but when I modify my commands as :

  ffmpeg -ss 526.623 -t 347 -i 'example.mp4' -c copy -avoid_negative_ts 1 -y res.mp4

  Output shows time=00:05:46.99 and actual video length is 00:05:52.13

  In the first case it added 5.13sec, in the second 5.14. Let’s take 5.14 for both cases that show that it has nothing to do with I-frame. There is no magic in this world (I guess). But what then ?

  UPD : It is GOP in the begging of the video. For this video it’s about 7 seconds.

• How do I get videoshow (or any other js package) to merge image and sound files to the length I specify rather than a constant length of 5 seconds ?

  5 décembre 2023, par Bragon

  I’m trying to take an image file and a sound file and merge them together into an mp4 file. To this end, I use videoshow.js which is basically a wrapper for fluent-ffmpeg.js. For some reason, videoshow always sets the duration of the output file to 5 seconds regardless of what I set the loop parameter to. And to top it all off, it fades out the sound towards the end of the clip.

  


  I’m happy for any solution to this even if it doesn’t include the use of videoshow or fluent-ffmpeg.

  


  const url = require('url');
const { smartLog } = require('../services/smart-log');
const { getFile, getDuration } = require('../services/file-service');
const videoshow = require('videoshow');
const path = require('path');
const FFmpeg = require('fluent-ffmpeg');
const fs = require('fs');

const imgToMP4 = (caption, sound, image, duration, output) => {
  smartLog('info', `Converting ${image}`);
  const images = [image];

  const videoOptions = {
    fps: 10,
    loop: duration,
    transition: false,
    videoBitrate: 1024,
    videoCodec: 'libx264',
    size: '640x?',
    audioBitrate: '128k',
    audioChannels: 2,
    format: 'mp4',
    pixelFormat: 'yuv420p',
  };

  videoshow([
    {
      path: image,
    },
  ])
    .audio(sound)
    .save(output)
    .on('start', function (command) {
      smartLog('info', `ffmpeg process started: ${image}`);
    })
    .on('error', function (err) {
      smartLog('error', err);
    })
    .on('end', function (output) {
      smartLog('info', `Video created: ${output}`);
    });
};