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• Ffmpeg - 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
}


  


• Encoding raw nv12 frames with ffmpeg

  3 août 2012, par nirjhor

  I am trying to encode raw frames in nv12 format. Frame rate is 15. I am using avcodec to encode. My capture device has a callback function which is activated when a raw viewfinder frame is available. I am copying the raw viewfinder frame and making a AVFrame from the data. Then I supply the frame to avcodec_encode_video as described in the api sample but somehow I am not getting expected result. I am using posix thread. I keep the raw frames on a buffer. Then my encoder thread collects data from the buffer and encodes it. The speed of encoding is too slow (h264 and mpeg1 -tested). Is it a problem with my threading or something else ? I am at loss. The output is mysterious. The whole encoding process is a single function and single threaded but I find a bunch of frame encoded at a time. How exactly does the encoder function ?Here is the code snippet for encoding :

  while(cameraRunning)
  
  {
  
      pthread_mutex_lock(&lock_encoder);
  
      if(vr->buffer->getTotalData()>0)
  
      {
  
          i++;
  
          fprintf(stderr,"Encoding %d\n",i);
  
          AVFrame *picture;
  
          int y = 0,x;
  
          picture = avcodec_alloc_frame();
  
          av_image_alloc(picture->data, picture->linesize,c->width, c->height,c->pix_fmt, 1);
  
          uint8_t* buf_source = new uint8_t[vr->width*vr->height*3/2];
  
          uint8_t* data = vr->buffer->Read(vr->width*vr->height*3/2);
  
          memcpy(buf_source,data,vr->width*vr->height*3/2);
  
          //free(&vr->buffer->Buffer[vr->buffer->getRead()-1][0]);
  
          /*for (y = 0; y < vr->height*vr->width; y++)
  
          {
  
              picture->data[0][(y/vr->width) * picture->linesize[0] + (y%vr->width)] = buf_source[(y/vr->width)+(y%vr->width)]x + y + i * 7;
  
              if(yheight*vr->width/4)
  
              {
  
                  picture->data[1][(y/vr->width) * picture->linesize[1] + (y%vr->width)] = buf_source[vr->width*vr->height + 2 * ((y/vr->width)+(y%vr->width))]128 + y + i * 2;
  
                  picture->data[2][(y/vr->width) * picture->linesize[2] + (y%vr->width)] = buf_source[vr->width*vr->height +  2 * ((y/vr->width)+(y%vr->width)) + 1]64 + x + i * 5;
  
              }
  
          }

  */

          for(y=0;yheight;y++) {
  
                      for(x=0;xwidth;x++) {
  
                          picture->data[0][y * picture->linesize[0] + x] = x + y + i * 7;
  
                      }
  
                  }
  
  
  
                  /* Cb and Cr */
  
                  for(y=0;yheight/2;y++) {
  
                      for(x=0;xwidth/2;x++) {
  
                          picture->data[1][y * picture->linesize[1] + x] = 128 + y + i * 2;
  
                          picture->data[2][y * picture->linesize[2] + x] = 64 + x + i * 5;
  
                      }
  
                  }
  
          free(buf_source);
  
          fprintf(stderr,"Data ready\n");
  
  
  
          outbuf_size = 100000 + c->width*c->height*3/2;
  
          outbuf = (uint8_t*)malloc(outbuf_size);
  
          fprintf(stderr,"Preparation done!!!\n");
  
          out_size = avcodec_encode_video(c, outbuf, outbuf_size, picture);
  
          had_output |= out_size;
  
          printf("encoding frame %3d (size=%5d)\n", i, out_size);
  
          fwrite(outbuf, 1, out_size, f);
  
          av_free(picture->data[0]);
  
          av_free(picture);
  
  
  
      }
  
      pthread_mutex_unlock(&lock_encoder);
  
  }

• Live555 truncates encoded data of FFMpeg

  22 novembre 2019, par Harshil Makwana

  I am trying to stream H264 based data using Live555 over RTSP.

  I am capturing data using V4L2, and then encodes it using FFMPEG and then passing data to Live555’s DeviceSource file, in that I using H264VideoStreamFramer class,

  Below is my codec settings to configure AVCodecContext of encoder,

  codec = avcodec_find_encoder_by_name(CODEC_NAME);
  
  if (!codec) {
  
      cerr << "Codec " << codec_name << " not found\n";
  
      exit(1);
  
  }
  
  
  
  c = avcodec_alloc_context3(codec);
  
  if (!c) {
  
      cerr << "Could not allocate video codec context\n";
  
      exit(1);
  
  }
  
  
  
  pkt = av_packet_alloc();
  
  if (!pkt)
  
      exit(1);
  
  
  
  /* put sample parameters */
  
  c->bit_rate = 400000;
  
  /* resolution must be a multiple of two */
  
  c->width = PIC_HEIGHT;
  
  c->height = PIC_WIDTH;
  
  /* frames per second */
  
  c->time_base = (AVRational){1, FPS};
  
  c->framerate = (AVRational){FPS, 1};
  
  c->gop_size = 10;
  
  c->max_b_frames = 1;
  
  c->pix_fmt = AV_PIX_FMT_YUV420P;
  
  c->rtp_payload_size = 30000;
  
  if (codec->id == AV_CODEC_ID_H264)
  
      av_opt_set(c->priv_data, "preset", "fast", 0);
  
  av_opt_set_int(c->priv_data, "slice-max-size", 30000, 0);
  
  /* open it */
  
  ret = avcodec_open2(c, codec, NULL);
  
  if (ret < 0) {
  
      cerr << "Could not open codec\n";
  
      exit(1);
  
  }

  And I am getting encoded data using avcodec_receive_packet() function. which will return AVPacket.

  And I am passing AVPacket’s data into DeviceSource file below is code snippet of my Live555 code :

  void DeviceSource::deliverFrame() {
  
      if (!isCurrentlyAwaitingData()) return; // we're not ready for the data yet
  
  
  
      u_int8_t* newFrameDataStart = (u_int8_t*) pkt->data;
  
      unsigned newFrameSize = pkt->size; //%%% TO BE WRITTEN %%%
  
      // Deliver the data here:
  
      if (newFrameSize > fMaxSize) { // Condition becomes true many times
  
          fFrameSize = fMaxSize;
  
          fNumTruncatedBytes = newFrameSize - fMaxSize;
  
      } else {
  
          fFrameSize = newFrameSize;
  
      }
  
      gettimeofday(&fPresentationTime, NULL); // If you have a more accurate time - e.g., from an encoder - then use that instead.
  
      // If the device is *not* a 'live source' (e.g., it comes instead from a file or buffer), then set "fDurationInMicroseconds" here.
  
      memmove(fTo, newFrameDataStart, fFrameSize);
  
  }

  But here, sometimes my packet’s size is getting more than fMaxSize value and as per LIVE555 logic it will truncate frame data, so that sometimes I am getting bad frames on my VLC,

  From Live555 forum, I get to know that encoder should not send packet whose size is more than fMaxSize value, so my question is :

  How to restrict encoder to limit size of packet ?

  Thanks in Advance,

  Harshil