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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.

• What is the best RTMP server to use ?

  12 septembre 2018, par Phudith Pattharakositkul

  I want to develop a web-application (for learning purposes) that receive an RTMP from a broadcaster (encoder) and translate that to HLS format to display it on the browser. I have tried to read up on this and found out that I need to setup a server to receive this RTMP and use ffmepg for file conversion. My question is, what is a good RTMP server to use ? I have done some research and see that a lot of people are using NGINX or RED5. I see an article that I could also use SRS https://github.com/ossrs/srs for simple server setup. I would like to know the pros and cons for each server type and why prefer one over another. Also, what if I would like to write my own file transcoding logic (instead of using ffmepg), how should this be done ?

  Thank you in advance !

• FFMPEG detect position of text and hide/delogo

  9 novembre 2016, par Ates Özen

  I’ve tried a lot of ways to do that. Is it possible to detect the position of a text in a video and hide/watermark it with delogo in ffmpeg ?

  You can see something like what i want in this video at 30th second :
  https://www.youtube.com/watch?v=HxexmWk2Yh0

  In my situation the text is not rectangled.