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• FFmpeg write silence if there is no data in pipe:0

  15 juillet 2023, par Oleksandr Petrenko

  I have an ffmpeg process that continiously writes PCM data from standard input to an mp3 file. The problem is that sometimes there can be pauses in data being sent to ffmpeg. Pauses may be very large, even up to an hour, but process is never closed. I want to get ffmpeg to write silence to file if there is no data in pipe:0. Is it possible to do only with ffmpeg or I need to implement it on my side ? If it is possible, then how can I do that ?
I tried to use some parameters and filters but I didn't found the thing I need.

  


  I'm new to ffmpeg and working with audio so I will be glad to see any assistance.

  


• How to call av_read_frame() when streamed data is not yet available ?

  16 janvier 2024, par CheekyChips

  I am streaming audio data and using the ffmpeg/libav libraries to process it in C++. I create a CustomIOContext and a read_packet function to provide the streamed data to ffmpeg, and I create an AVFormatContext using that CustomIOContext.

  


  I want to loop through all available data and extract packets using av_read_frame(), and then when there is not enough data left to create a packet I want to wait until I receive more data and then loop again through the new data. However, I can't figure out what to return in my read_packet function below to tell ffmpeg to wait until more data is available. Ffmpeg seems to require all data to be available now. When I have no data to return, ffmpeg seems to think it's the end of the file, when actually it just isn't ready yet. I have tried returning AVERROR(EAGAIN) but I still have problems. It seems like I get random decoder-specific error messages, because it thinks the input is invalid (when actually it is just not available yet), and then once I have the input and I try calling av_read_frame() again, it immediately returns a negative error code because it got into a bad state.

  


  What do I need to do to be able to loop through all the available data using av_read_frame(), and then pause and wait until more data arrives ? How do I keep ffmpeg happy ?

  


  // -------- Set up  --------
size_t ioContextBufferSize = 4096;
avioContextBuffer = avAllocateEmptyBuffer(ioContextBufferSize);
avioContext = avio_alloc_context(avioContextBuffer.ptr,
                         ioContextBufferSize,
                    0, // bWriteable (1=true,0=false)
                        &(opaque),
                        read_packet,
                        0, // Write callback function
                        0)}; // Seek function not provided

AVFormatContext* inContext = avformat_alloc_context();
inContext->pb = avioContext;
inContext->flags = AVFMT_FLAG_CUSTOM_IO;

avformat_open_input(&inContext, "", nullptr, nullptr);
inputPacket = av_packet_alloc();


  


  // -------- Loop and read data -------
// (the second time we reach this while loop, it never enters the loop :(
//
while ((ret = av_read_frame(inContext, inputPacket)) >= 0) {
  .. do stuff with inputPacket
}


  


  // -------- read_packet function -----
// copies data into ffmpeg's internal buffer. What do I return here???
//
static int read_packet(void* opaque, uint8_t* avioContextBuffer, int ioContextBufferSize) {
  OpaqueDataWrapper* streamedData = static_cast(opaque);

  size_t bytesToRead = std::min((size_t)ioContextBufferSize, streamedData->remainingBytes());

  if (!bytesToRead) {
    // We need to wait for more data to arrive! What do I return here to tell ffmpeg to wait a while? 
    if (streamedData->streamStillOpen()) {
      return AVERROR(EAGAIN);
    } else {
      return AVERROR_EOF;
    }
  }
  ... otherwise copy the next bit of data
}


  


• How to packet encoded AAC data to flv file with ffmpeg ?

  1er juillet 2015, par Jerikc XIONG

  I have captured the Audio data from Android Microphone and encoded them by MediaCodec.

  My question is :

  How to packet encoded AAC data to flv with ffmpeg ?