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• Why do these two ffmpeg files differ (piping vs file output) ?

  4 novembre 2017, par Julian Grinblat

  I have a source sound audio.mp3 and I want to convert it into audio.aiff.
  When I do

  ffmpeg -i audio.mp3 -acodec pcm_s16le -ac 1 -ar 44100 -vn audio.aiff

  I get output a file tim_tum.aiff exactly as I expect it which is playable. However, what I found is that when I do

  ffmpeg -i audio.mp3 -acodec pcm_s16le -ac 1 -ar 44100 -vn -f aiff pipe:1 > audio_pipe.aiff

  I get an audio_pipe.aiff file which is unplayable and is different from the original audio.aiff file, as evidenced by

  $ diff audio.aiff audio_pipe.aiff
  
  Binary files audio.aiff and audio_pipe.aiff differ

  I would expect both files to be identical and cannot figure out why they would come out differently, but most importantly, why is one file playable while the other isn’t ?

• Linux & C : How to set file reading priority in multi-process program while recording mp4 files

  31 octobre 2017, par bala ece17

  This is for an assignment I’m not looking for you to suggest me the answer. I just need someone to point me in the right direction, maybe with a line or two of sample code.

  I need to figure out how to set the priority of a recording mp4 files within my program. To the point :

  i am trying to record from three cameras (1-HD and 2 analog cameras) at the same time and creating its tar file after each recording of duration 60seconds.

  so after a set of records completed, i am taring those files. in doing that i am experiencing frame skip in only HD camera, remain 2 analog cameras are fine.hence forth i decided to set high priority for recording and low priority for taring those files.

  please suggest me some ideas to set the priority, that neglect the frame skip.

  Any help/guidance is appreciated :)

• Haskell - Turning multiple image-files into one video-file using the ffmpeg-light package

  25 avril 2021, par oRole

  Background
  
I wrote an application for image-processing which uses the ffmpeg-light package to fetch all the frames of a given video-file so that the program afterwards is able to apply grayscaling, as well as edge detection alogrithms to each of the frames.
  

  


  Now I'm trying to put all of the frames back into a single video-file.

  


  Used Libs
  
ffmpeg-light-0.12.0
  
JuicyPixels-3.2.8.3
  
...

  


  What have I tried ?
  
I have to be honest, I didn't really try anything because I'm kinda clueless where and how to start. I saw that there is a package called Command which allows running processes/commands using the command line. With that I could use ffmpeg (not ffmpeg-light) to create a video out of image-files which I would have to save to the hard drive first but that would be kinda hacky.

  
Within the documentation of ffmpeg-light on hackage (ffmpeg-light docu) I found the frameWriter function which sounds promising.

  


  frameWriter :: EncodingParams -> FilePath -> IO (Maybe (AVPixelFormat, V2 CInt, Vector CUChar) -> IO ()) 


  


  I guess FilePath would be the location where the video file gets stored but I can't really imagine how to apply the frames as EncodingParams to this function.

  


  Others
  
I can access :
  

  


  

  • r, g, b, a as well asy. a values
    

  


  • image width / height / format

  


  


  Question
  
Is there a way to achieve this using the ffmpeg-light package ?

  


  As the ffmpeg-light package lacks of documentation when it comes to conversion from images to video, I really would appreciate your help. (I do not expect a fully working solution.)

  


  Code
  
The code that reads the frames :

  


  -- Gets and returns all frames that a given video contains
getAllFrames :: String -> IO [(Double, DynamicImage)]
getAllFrames vidPath = do 
  result <- try (imageReaderTime $ File vidPath) :: IO (Either SomeException (IO (Maybe (Image PixelRGB8, Double)), IO()))
  case result of 
    Left ex -> do 
                 printStatus "Invalid video-path or invalid video-format detected." "Video" 
                 return []
    Right (getFrame, _) -> addNextFrame getFrame [] 

-- Adds up all available frames to a video.
addNextFrame :: IO (Maybe (Image PixelRGB8, Double)) -> [(Double, DynamicImage)] -> IO [(Double, DynamicImage)]
addNextFrame getFrame frames = do
  frame <- getFrame
  case frame of 
    Nothing -> do 
                 printStatus "No more frames found." "Video"
                 return frames
    _       -> do                             
                 newFrameData <- fmap ImageRGB8 . swap . fromJust <$> getFrame 
                 printStatus ("Frame: " ++ (show $ length frames) ++ " added.") "Video"
                 addNextFrame getFrame (frames ++ [newFrameData]) 


  


  Where I am stuck / The code that should convert images to video :

  


  -- Converts from several images to video
juicyToFFmpeg :: [Image PixelYA8] -> ?
juicyToFFmpeg imgs = undefined