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• Compression of a video with constant background

  28 juin 2017, par Spirou003

  (sorry if my english is bad, I can read it but I don’t write it quite well...)

  I want to compress some videos, which have two particularities :

  • there is a background that covers 90% of the area, during the whole video
  • most of the others elements can be separately described by a picture in move

  My videos are like this one, and don’t have audio. As you can see, almost everything can be described only by using a fixed background, few small images in move, plus a noise. Moreover, this noise will be almost nul and then an entropic coding would be very efficient. I think it will produce tiny files (< 5 Mo) even if the duration is in hours, a result that is very appreciable since I have actually recorded 30h of game (actual size is 3 Go).

  Is there any way to get new video files, that benefit of these informations ? If yes, what are the implication of a such encoding for watching these videos with Windows Media Player, or for usage with ffmpeg ?

  I searched with Google after anything that can help me, but I don’t know which keyword I can use for this, then I didn’t found anything usefull :-(

  Thanks in advance :-)

  PS : another example, the video is accelerated but shows the interesting moves

• Download youtube video duration using youtube-dl PHP and ffmpeg

  21 juin 2017, par user3285828

  Is there any more efficient way to download youtube videos at a specific start and end time using youtube-dl and ffmpeg in PHP.

  I currently have this, which does work, it first downloads the whole video to an mp3 file, and then crops that file to the range I set using ffmpeg, but when I only want 30 seconds or so of a 20 minute video, waiting for the full video to download doesn’t seem the best way to do it.

  <?php
  
  require __DIR__ . '/vendor/autoload.php';
  
  
  
  use YoutubeDl\YoutubeDl;
  
  
  
  $dl = new YoutubeDl([
  
      'extract-audio' => true,
  
      'audio-format' => 'mp3',
  
      'audio-quality' => 0, // best
  
      'output' => 'videoname.%(ext)s',
  
  ]);
  
  $dl->setDownloadPath('C:\youtubevideos');
  
  $video = $dl->download('https://www.youtube.com/watch?v=oDAw7vW7H0c');
  
  
  
  $start = 60; // Start 60 seconds in to the video
  
  $duration = 30; // Get 30 seconds after $start
  
  $fullVideo = "C:\youtubevideos\videoname.mp3";
  
  $shortVideo = "C:\youtubevideos\short\shortversion.mp3"; // create 30 seconds
  
  exec("ffmpeg -ss $start -i $fullVideo -t $duration -c copy $shortVideo");
  
  exec("DEL $fullVideo");

  I am using youtube dl PHP https://github.com/norkunas/youtube-dl-php

• How to do Slow Motion video in IOS

  4 mai 2022, par 2vision2

  I have to do "slow motion" in a video file along with audio, in-between some frames and need to store the ramped video as a new video.

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  Ref : http://www.youtube.com/watch?v=BJ3_xMGzauk (watch from 0 to 10s)

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  From my analysis, I've found that AVFoundation framework can be helpful.

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  Ref :&#xA;http://developer.apple.com/library/ios/#documentation/AudioVideo/Conceptual/AVFoundationPG/Articles/00_Introduction.html

  &#xA;&#xA;

  Copy and pasted from the above link :

  &#xA;&#xA;

  "&#xA;Editing&#xA;AV Foundation uses compositions to create new assets from existing pieces of media (typically, one or more video and audio tracks). You use a mutable composition to add and remove tracks, and adjust their temporal orderings. You can also set the relative volumes and ramping of audio tracks ; and set the opacity, and opacity ramps, of video tracks. A composition is an assemblage of pieces of media held in memory. When you export a composition using an export session, it's collapsed to a file.&#xA;On iOS 4.1 and later, you can also create an asset from media such as sample buffers or still images using an asset writer.

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  "

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  Questions :&#xA;Can I do " slow motion " the video/audio file using the AVFoundation framework ? Or Is there any other package available ? If i want to handle audio and video separately, please guide me how to do ?

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  Update : : Code For AV Export Session :

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   NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *outputURL = paths[0];
    NSFileManager *manager = [NSFileManager defaultManager];
    [manager createDirectoryAtPath:outputURL withIntermediateDirectories:YES attributes:nil error:nil];
    outputURL = [outputURL stringByAppendingPathComponent:@"output.mp4"];
    // Remove Existing File
    [manager removeItemAtPath:outputURL error:nil];
    AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset:self.inputAsset presetName:AVAssetExportPresetLowQuality];
    exportSession.outputURL = [NSURL fileURLWithPath:outputURL]; // output path;
    exportSession.outputFileType = AVFileTypeQuickTimeMovie;
    [exportSession exportAsynchronouslyWithCompletionHandler:^(void) {
        if (exportSession.status == AVAssetExportSessionStatusCompleted) {
            [self writeVideoToPhotoLibrary:[NSURL fileURLWithPath:outputURL]];
            ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
            [library writeVideoAtPathToSavedPhotosAlbum:[NSURL fileURLWithPath:outputURL] completionBlock:^(NSURL *assetURL, NSError *error){
                if (error) {
                    NSLog(@"Video could not be saved");
                }
            }];
        } else {
            NSLog(@"error: %@", [exportSession error]);
        }
    }];


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