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• How to do Slow Motion video in IOS

  17 janvier 2017, 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.

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

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

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

  Copy and pasted from the above link :

  "
  Editing
  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.
  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.

  "

  Questions :
  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 ?

  Update : : Code For AV Export Session :

   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]);
  
          }
  
      }];

• 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.

  



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

  



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

  



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

  



  Copy and pasted from the above link :

  



  "
Editing
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.
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.

  



  "

  



  Questions :
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 ?

  



  Update : : Code For AV Export Session :

  



   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]);
        }
    }];


  


• How to run a video on chromium/lubuntu smoothly on a low-end machine ?

  29 juillet 2020, par Altuğ Ceylan

  the cpu of the machine is Atom X5-Z8350 with a ram size of 4 GB. It does not have an external gpu.
The problem is that when it runs a video on chromium such as a youtube video, it stutters and fps drop happens. I found out that the cpu supports h264 and vp8, and chromium only supports vp-8 and vp-9. Therefore, I used ffmpeg to transcode a video I downloaded from youtube to see if it was going to help.
I used the following script from my github repository which also contains driver update scripts etc

  


  
#$1 input filename
#$2 good realtime best
#$3 --cpu-used for best and good deadline valid values are from 0 to 5 for realtime 0 to 15
#$4 tile columns allow multi threading use powers of 2 eg 2=4
#$5 no threads to use
#$6 minrate around 2k is good for 1080p60
#$7 out filename
# -b:v bitrate 512k maybe too low for 720p30 try 1500k to 2000k 
#for fast/quality use realtime 6-7 
#for very good quality use good 2
start=$(date +%s.%N)
ffmpeg -i $1 -r 30 -g 90 -s 1280x720 -aspect 16:9 -c:v libvpx -deadline $2 -row-mt 1 -b:v 2500k -threads $5 -tile-columns $4 -cpu-used $3 -minrate $6 -bufsize 3000k -maxrate 3000k -crf 30 -frame-parallel 1 $7.webm
duration=$(echo "$(date +%s.%N) - $start" | bc)
execution_time=`printf "%.2f seconds" $duration`
echo "Script Execution Time: $execution_time"



  


  I changed crf to 5, -r to 120 -s to 1920x1080 and passed $2 as realtime, $3 as 7, $4 as 2 , $5 as 4, $6 as 2000k, I used the following video https://www.youtube.com/watch?v=jZKvJY6gDfg. It was a lot better than before, the chromium was having hard time running 720p30 but now it actually ran the 1080p120 video with minor tear and fps drops. How can I prevent the tears and the fps drops from happening ?