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• Can't compile project with ffmpeg-light

  27 octobre 2016, par wowofbob

  Compilation of any project which uses openFile function from Codec.FFmpeg.Decode fails with error :

  Couldn't match type ‘GHC.IO.Exception.IOException’ with ‘[Char]’
           arising from a functional dependency between:
             constraint ‘mtl-2.2.1:Control.Monad.Error.Class.MonadError
                           String IO’
               arising from a use of ‘openFile’
             instance ‘mtl-2.2.1:Control.Monad.Error.Class.MonadError
                         GHC.IO.Exception.IOException IO’
               at <no location="location" info="info"></no>

  As an example, compilation of this fails :

  openVideoFile :: String -> IO ()
  
  openVideoFile filePath = do
  
  
  
    initFFmpeg
  
  
  
    avFmtCtx <- openFile filePath
  
  
  
    return ()

  I guess the reason is that there is no ready instance of MonadError String IO. But, when I add a dummy instance like this :

  instance MonadError String IO where
  
    throwError _   = undefined
  
    catchError _ _ = undefined

  I’m getting another error :

  Functional dependencies conflict between instance declarations:
 instance MonadError String IO
   -- Defined at src/Video/Play/Base.hs:20:10
 instance [safe] MonadError GHC.IO.Exception.IOException IO
   -- Defined in ‘Control.Monad.Error.Class’

  I don’t know how to force compiler to use MonadError String IO instace here.

  • Should I assure GHC that my instance is better ?
  • Do I have a wrong environment setup ? I’m using ffmpeg-light clone from here and resolver lts-7.2. Host OS is Ubuntu.
  • There is commit which replaces import of Control.Monad.Error.Class by Control.Monad.Except. But, Control.Monad.Error.Class is still used in Codec.FFmpeg.Common. First time I thought it caused a problem. But it turns out that Control.Monad.Except just re-exports MonadError class from Control.Monad.Error.Class. So, it’s not a problem.

• Are there people interested in converting ffmpeg source to Go ?

  30 septembre 2018, par No One

  After seeing that Go compiler have been converted from C to Go I thought same for ffmpeg ? Don’t want to go deep into reasons as I think they are obvious. It was very hard to be so close to the have rich library as ffmpeg in other language. It was even hard to make bindings for that scale of library. I’m not enough advanced to start something like this myself, so is there anybody else interested in this ? If yes then where this question worth to be addressed, so people interested in this may have discussion ?

  (Seems not enough obvious so adding some details.)

  For applications which use large amount of commands with different complexity it is hard to read the code as it’s not actually a code. Instead, it’s commands which you will need to understand by reading docs from ffmpeg’s docs page. I had used ffmpeg before in Nodejs and there was lots of logic of manipulating command string. Also sometimes in windows it was ending with cmd limitations error. When you are working with some language it is nice to see whole logic in that language. So you know go ? than you know everything that is happening with this code without even going off from code and reading docs of another application.

  There may be some benefits from executing stuff in goroutines so you can handle concurrency in the way you want not in the way it is implemented in ffmpeg.

  Build faster with Go.

  Less code.

  Possibility to split code into smaller packages.

  Also if you are familiar why community converted compiler from C to Go than I think some reasons will fit too.

• Java Desktop Capture

  10 mars 2016, par Kurt

  I want to continuously capture the entire desktop inside of a java application. As I’m capturing, I’d like to chunk the stream of data into small video files (mp4, WebM) for storage. From my research, it would seem that the Robot Java class and the FFmpeg tool are my best options. However, Robot seems to best-fit the use case of obtaining images, not videos. FFmpeg seems like it may support this, but I’ve struggled to find definitive documentation. I’m looking to emulate what can be done through Chrome’s getUserMedia and desktopCapture APIs along with the MediaStreamRecorder JavaScript library. Does anyone have a suggestion for a similar and elegant solution in Java ?