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• How to trim a video using FFmpeg in Objective-C for iOS application

  13 juillet 2015, par AnujAroshA

  I am trying to implement a sample iOS application that can trim a bundled video (.mp4) using FFmpeg library in Objective-C environment.

  I used this script to compile and build the FFmpeg for iOS. Those libraries was added to the project but now I’m not sure how to continue it. How can I find which function do the trim behaviour and what are the supportive codecs and etc.

  I am interesting do achieve this with out any wrapper but directly accessing the library functions. How can I do this ?

  Update : 1

  I believe following code snippet will contain the input video file details in a stream

  NSString *filePath = [[NSBundle mainBundle] pathForResource:@"KeseMase" ofType:@".mp4"];
  
  
  
  AVInputFormat *inputFormat = av_find_input_format([@"mp4" UTF8String]);
  
  
  
  const char *utf8FilePath = [filePath UTF8String];
  
  
  
  avformat_open_input(&pFormatCtx, utf8FilePath, inputFormat, nil);

  Or does it contain only the header information of the video file ?

  Update : 2

  With following code, I was able to convert input video to a stream of AVPacket and store them in a NSMutableArray

  - (BOOL)readFrameIntoPacket:(AVPacket *)packet error:(NSError *__autoreleasing *)error
  
  {
  
      BOOL continueReading = YES;
  
  
  
      int frameReadValue = av_read_frame(pFormatCtx, packet);
  
  
  
      if (frameReadValue == 0)
  
      {
  
          NSLog(@"%s - %d # Read next frame", __PRETTY_FUNCTION__, __LINE__);
  
          continueReading = YES;
  
  
  
          NSValue *value = [NSValue valueWithBytes:&packet objCType:@encode(AVPacket)];
  
          [srcPktArr addObject:value];
  
      }
  
      else
  
      {
  
          continueReading = NO;
  
          av_free_packet(packet);
  
      }
  
      return continueReading;
  
  }

  Tasks remain to solve the question are :

  1.) How to use those AVPackets to and write a Video file

  2.) How to give a start time and end time and write only that part to a video file

  Update : 3

  Okay... then I try to write those packets to an out put file like below

  - (BOOL)writePacket:(AVPacket *)packet error:(NSError *__autoreleasing *)error
  
  {
  
      int writeValue = av_write_frame(outputContext, packet);
  
  
  
      if (writeValue == 0)
  
      {
  
          return YES;
  
      }
  
      else if (writeValue == 1)
  
      {
  
          return YES;
  
      }
  
      else
  
      {
  
          return NO;
  
      }
  
  }

  and ended up with following error

  [mp4 @ 0x1c04a200] Invalid packet stream index : 17467852

  Update : 4

  Okay guys, I get this far.

• Encoding base64 frames to a video with ffmpeg from a C# .NET application

  9 mars 2021, par nmkd

  I have PNG images stored as base64 strings in RAM and want to encode those into a video using ffmpeg, without having to store them on the disk first.

  


  Is this possible at all ? FFmpeg's image2pipe demuxer allows piping images from stdin, but this doesn't seem to work for base64 strings.

  


• How to capture app audio using LIBAV on QT application

  17 février 2021, par Aramis Romero

  I am working on a QT application that is intended to stream its gui and audio. Currently i'm able to capture the rendered frames using QOffscreenSurface(there is an example called rendercontrol in QT sources) and to create the AVFrame for each one. The stream looks good, but now i need to add the application's audio. I know there are ways of capturing audio from system audio input devices, but i can't figure out how to obtain the audio samples from the app(windows or linux).