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• CGO : How do you use pointers in Golang to access data from an array in C

  23 avril 2018, par nevernew

  I’m writing an app for the windows platform using FFmpeg and it’s golang wrapper goav, but I’m having trouble understanding how to use the C pointers to gain access to the data array they point to.

  I’m trying to get the data stored in the AVFrame class and use Go to write it to a file, and eventually a texture in OpenGl to make a video player with cool transitions.

  I think understanding how to cast and access the C data will make coding this a lot easier.

  I’ve stripped out all the relevant parts of the C code, the wrapper and my code, shown below :

  C code - libavutil/frame.h

  #include 
  
  
  
  typedef struct AVFrame {
  
  #define AV_NUM_DATA_POINTERS 8
  
      uint8_t *data[AV_NUM_DATA_POINTERS];
  
  }

  Golang goav wrapper - I don’t really know whats going on here with the unsafe.Pointers and casting but it gives me access to the underlying C code

  package avutil
  
  
  
  /*
  
      #cgo pkg-config: libavutil
  
      #include <libavutil></libavutil>frame.h>
  
      #include 
  
  */
  
  import "C"
  
  import (
  
      "unsafe"
  
  )
  
  
  
  type Frame C.struct_AVFrame
  
  
  
  func AvFrameAlloc() *Frame {
  
      return (*Frame)(unsafe.Pointer(C.av_frame_alloc()))
  
  }
  
  
  
  func Data(f *Frame) *uint8 {
  
      return (*uint8)(unsafe.Pointer((*C.uint8_t)(unsafe.Pointer(&amp;f.data))))
  
  }

  My Golang code

  package main
  
  
  
  import "github.com/giorgisio/goav/avutil"
  
  
  
  func main() {
  
      videoFrame := avutil.AvFrameAlloc()
  
  
  
      data := avutil.Data(videoFrame)
  
  
  
      fmt.Println(data) // here i want the values from data[0] to data[7], but how?
  
  }

• avformat/mov : add option max_stts_delta

  27 novembre 2021, par Gyan Doshi

  avformat/mov : add option max_stts_delta
  Very high stts sample deltas may occasionally be intended but usually
  
  they are written in error or used to store a negative value for dts correction
  
  when treated as signed 32-bit integers.
  This option lets the user set an upper limit, beyond which the delta is clamped to 1.
  
  Values greater than the limit if negative when cast to int32 are used to adjust onward dts.
  Unit is the track time scale. Default is UINT_MAX - 48000*10 which
  
  allows upto a 10 second dts correction for 48 kHz audio streams while
  
  accommodating 99.9% of uint32 range.
  Signed-off-by : Gyan Doshi <ffmpeg@gyani.pro>
  
  Reviewed-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] doc/demuxers.texi
  • [DH] libavformat/isom.h
  • [DH] libavformat/mov.c

• MobileFFmpeg - get progress of concatenation of a video

  18 mai 2020, par STerrier

  Is there a way to grab the progress of the concatenation using Mobile FFmpeg ? Mobile FFmpeg displays stats by default in the console and I can see the time length of the video which I want but I can't find a way to grab it so I can create a progress bar.

  



  Data displayed in the console
2658560kB time=01:30:40.00 bitrate=4003.5kbits/s speed=60.9x \rframe=137002 fps=1524 q=-1.0
2678272kB time=01:31:20.00 bitrate=4003.7kbits/s speed=61x \rframe=138252 fps=1528 q=-1.0

  



  func encodeWebp(m3u8: String, completed: () -> Void){
    guard let sessionid = sessionID else {return}

    let lastName: String = m3u8
    let docFolder = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0]
    let output = URL(fileURLWithPath: docFolder + "/OfflineSession/\(sessionid)").appendingPathComponent("\(lastName).mp4")
    let outputTxt = URL(fileURLWithPath: docFolder + "/OfflineSession/\(sessionid)").appendingPathComponent("\(lastName).txt")
    let fileName = "\(m3u8)_ffmpegData.txt"
    let textFile = URL(fileURLWithPath: docFolder).appendingPathComponent("OfflineSession/\(sessionid)/\(fileName)")

    let ffmpegCommand = "-f concat -i \(textFile) -c:v copy -c:a copy \(output) -progress \(outputTxt)"

    MobileFFmpeg.execute(ffmpegCommand)

    completed()

}


  



  GITHUB - Mobile FFmpeg
https://github.com/tanersener/mobile-ffmpeg