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• ffmpeg concat drops audio frames

  5 octobre 2017, par Shaun

  I have an mp4 file and I want to take two sequential sections of the video out and render them as individual files, later recombining them back into the original video. For instance, with my video video.mp4, I can run

  ffmpeg -i video.mp4 -ss 56 -t 4 out1.mp4
  
  ffmpeg -i video.mp4 -ss 60 -t 4 out2.mp4

  creating out1.mp4 which contains 00:00:56 to 00:01:00 of video.mp4, and out2.mp4 which contains 00:01:00 to 00:01:04. However, later I want to be able to recombine them again quickly (i.e., without reencoding), so I use the concat demuxer,

  ffmpeg -f concat -safe 0 -i files.txt -c copy concat.mp4

  where files.txt contains

  file out1.mp4
  
  file out2.mp4

  which theoretically should give me back 00:00:56 to 00:01:04 of video.mp4, however there are always dropped audio frames where the concatenation occurs, creating a very unpleasant sound artifact, an audio blip, if you will.

  

  I have tried using async and -af apad on initially creating the two sections of the video but I am still faced with the same problem, and have not found the solution elsewhere. I have experienced this issue in multiple different use cases, so hopefully this simple example will shed some light on the real problem.

• Array Getting Lost While Passing From C++ to C Using Callback [duplicate]

  23 décembre 2020, par Abhishek Sharma

  I am trying to write Video Using FFmpeg by generating frame at run time using direct3d and the frames are generated using sharp dx at c# and I use window runtime to callback to c# to generate Frame And return Platform::Array of Byte ;

  


  so for writing video using FFmpeg, I used C code that writes video, and to ask for generating frame I implemented a callback to generate a frame and all that in StaticLib

  


  uint8_t*(*genrate_frame_callback)(int) = NULL;   


  


  now in C-File, I call fill_image to get the frame and write to the video

  


  static void fill_image(int frame_index, int width, int height)
{
    int x, y, i;

    i = frame_index;
    auto result = genrate_frame_callback(frame_index);// after passing this point while using debugger reults single element not even array
    .
    .
    .
    code to write video
    
}


  


  now when I call to Write Video before that pass this function to the callback that is in the c++ file in a Window Runtime Component that reference to static lib

  


  uint8_t* genrate_frame(int args)&#xA;{&#xA;    auto frame = FireGenrateFramet(args); // returns Platform::Array<byte>&#xA;    vector v(frame->begin(), frame->end());&#xA;    return v.data();// data is abilabe to this point &#xA;}&#xA;</byte>

  


  now the result variable contains a single element
I am new to c++ and c and unable to understand why is data not passed to the function using call back

  


  Edit :

  


  then can you help me with how to pass Data I tried using the global Scope Variable c++ file too but still,
it gets lost,
but after introducing another call back to read data stored in global Variable it read the whole data correctly

  


  vector frame_v;
uint8_t* genrate_frame(int args)
{
    auto frame = FireGenrateFrame(args);
     vector v(frame->begin(), frame->end());
    frame_v = v;
    return v.data();// this loose the Same 
}

uint8_t read_pixal(int args)
{
    return frame_v[args];// where as it read out correctly
}


  


  but I don't want to store and add new call back an read from their just pass the array

  


• A nice comparison of mics

  3 juin 2010

  DVEStore has done a great comparison of different types of microphones on video. Audio is a black art, and folks rarely put in the time to do A/B/C comparisons. We tend to just default to a set of mics that we’ve decided are "good enough" and then don’t go back to reevaluate.