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• How to merge two audio files into one stereo file in FFmpeg？

  12 août 2021, par TW520

  input :

  


  


  Two audio file, It may be stereo or mono.

  


  


  output :

  


  


  

  • A stereo file, and the stereo FL uses one file all channels, and FR uses other file all channels.

  


  • The total duration is based on the longest file.

  


  • I hope it can be achieved through FFmpeg.

  


  


  


  There are four case :

  


  

  • mono + mono -> stereo

  


  • mono + stereo -> stereo

  


  • stereo + mono -> stereo

  


  • stereo + stereo -> stereo

  


  


  I hope someone can help me, I am a newbie to FFmpeg.

  


• ffmpeg live stream latency

  22 août 2014, par Alex Fu

  I’m currently working on live streaming video from device A (source) to device B (destination) directly via local WiFi network.

  I’ve built FFMPEG to work on the Android platform and I have been able to stream video from A -> B successfully at the expense of latency (takes about 20 seconds for a movement or change to appear on screen ; as if the video was 20 seconds behind actual events).

  Initial start up is around 4 seconds. I’ve been able to trim that initial start up time down by lowering probesize and max_analyze_duration but the 20 second delay is still there.

  I’ve sprinkled some timing events around the code to try an figure out where the most time is being spent...

  • naInit : 0.24575 sec
  • naSetup : 0.043705 sec

  The first video frame isn’t obtained until 0.035342 sec after the decodeAndRender function is called. Subsequent decoding times can be illustrated here : http://jsfiddle.net/uff0jdf7/1/ (interactive graph)

  From all the timing data i’ve recorded, nothing really jumps out at me unless I’m doing the timing wrong. Some have suggested that I am buffering too much data, however, as far as I can tell, I’m only buffering an image at a time. Is this too much ?

  Also, the source video that’s coming in is in the format of P264 ; it’s a custom implementation of H264 apparently.

  jint naSetup(JNIEnv *pEnv, jobject pObj, int pWidth, int pHeight) {
  
    width = pWidth;
  
    height = pHeight;
  
  
  
    //create a bitmap as the buffer for frameRGBA
  
    bitmap = createBitmap(pEnv, pWidth, pHeight);
  
    if (AndroidBitmap_lockPixels(pEnv, bitmap, &pixel_buffer) < 0) {
  
      LOGE("Could not lock bitmap pixels");
  
      return -1;
  
    }
  
  
  
    //get the scaling context
  
    sws_ctx = sws_getContext(codecCtx->width, codecCtx->height, codecCtx->pix_fmt,
  
        pWidth, pHeight, AV_PIX_FMT_RGBA, SWS_BILINEAR, NULL, NULL, NULL);
  
  
  
    // Assign appropriate parts of bitmap to image planes in pFrameRGBA
  
    // Note that pFrameRGBA is an AVFrame, but AVFrame is a superset
  
    // of AVPicture
  
    av_image_fill_arrays(frameRGBA->data, frameRGBA->linesize, pixel_buffer, AV_PIX_FMT_RGBA, pWidth, pHeight, 1);
  
    return 0;
  
  }
  
  
  
  void decodeAndRender(JNIEnv *pEnv) {
  
    ANativeWindow_Buffer windowBuffer;
  
    AVPacket packet;
  
    AVPacket outputPacket;
  
    int frame_count = 0;
  
    int got_frame;
  
  
  
    while (!stop && av_read_frame(formatCtx, &packet) >= 0) {
  
      // Is this a packet from the video stream?
  
      if (packet.stream_index == video_stream_index) {
  
  
  
        // Decode video frame
  
        avcodec_decode_video2(codecCtx, decodedFrame, &got_frame, &packet);
  
  
  
        // Did we get a video frame?
  
        if (got_frame) {
  
          // Convert the image from its native format to RGBA
  
          sws_scale(sws_ctx, (uint8_t const * const *) decodedFrame->data,
  
              decodedFrame->linesize, 0, codecCtx->height, frameRGBA->data,
  
              frameRGBA->linesize);
  
  
  
          // lock the window buffer
  
          if (ANativeWindow_lock(window, &windowBuffer, NULL) < 0) {
  
            LOGE("Cannot lock window");
  
          } else {
  
            // draw the frame on buffer
  
            int h;
  
            for (h = 0; h < height; h++) {
  
              memcpy(windowBuffer.bits + h * windowBuffer.stride * 4,
  
                     pixel_buffer + h * frameRGBA->linesize[0],
  
                     width * 4);
  
            }
  
            // unlock the window buffer and post it to display
  
            ANativeWindow_unlockAndPost(window);
  
  
  
            // count number of frames
  
            ++frame_count;
  
          }
  
        }
  
      }
  
  
  
      // Free the packet that was allocated by av_read_frame
  
      av_free_packet(&packet);
  
    }
  
  
  
    LOGI("Total # of frames decoded and rendered %d", frame_count);
  
  }

• use ffmpeg to cut video,the video will have extra duration

  17 juin 2021, par Venus

  ffmpeg -ss 2 -i input.mp4 -c copy -t 5 out.mp4


  


  after I executed the ffmpeg command.
  
the out.mp4 total have 7 seconds,it starts from the second frame of input.mp4 to the seventh frame of input.mp4.
  
It only has 5 effective seconds of the input.mp4, the last 2 seconds of input.mp4 is empty.