Recherche avancée

Sur d’autres sites (7815)

• Creating a usable H.264 video file

  4 mai 2019, par Ethan McTague

  I am trying to use libavcodec to generate an mp4 video file from individual frames. Each input frame is a qt QImage, and the output file is written to using the Qt QFile class.

  I’ve done this through a VideoTarget class which opens the given ’target’ file when initialized, records frames when addFrame(image) is called, and then saves/closes the file when its destructor is called.

  The class has the following fields :

  AVCodec* m_codec = nullptr;
  
  AVCodecContext *m_context = nullptr;
  
  AVPacket* m_packet = nullptr;
  
  AVFrame* m_frame = nullptr;
  
  
  
  QFile m_target;

  And looks like this :

  VideoTarget::VideoTarget(QString target, QObject *parent) : QObject(parent), m_target(target)
  
  {
  
      // Find video codec
  
      m_codec = avcodec_find_encoder_by_name("libx264rgb");
  
      if (!m_codec) throw std::runtime_error("Unable to find codec.");
  
  
  
      // Make codec context
  
      m_context = avcodec_alloc_context3(m_codec);
  
      if (!m_context) throw std::runtime_error("Unable to allocate codec context.");
  
  
  
      // Make codec packet
  
      m_packet = av_packet_alloc();
  
      if (!m_packet) throw std::runtime_error("Unable to allocate packet.");
  
  
  
      // Configure context
  
      m_context->bit_rate = 400000;
  
      m_context->width = 1280;
  
      m_context->height = 720;
  
      m_context->time_base = (AVRational){1, 60};
  
      m_context->framerate = (AVRational){60, 1};
  
      m_context->gop_size = 10;
  
      m_context->max_b_frames = 1;
  
      m_context->pix_fmt = AV_PIX_FMT_RGB24;
  
  
  
      if (m_codec->id == AV_CODEC_ID_H264)
  
          av_opt_set(m_context->priv_data, "preset", "slow", 0);
  
  
  
      // Open Codec
  
      int ret = avcodec_open2(m_context, m_codec, nullptr);
  
      if (ret < 0) {
  
          throw std::runtime_error("Unable to open codec.");
  
      }
  
  
  
      // Open file
  
      if (!m_target.open(QIODevice::WriteOnly))
  
          throw std::runtime_error("Unable to open target file.");
  
  
  
      // Allocate frame
  
      m_frame = av_frame_alloc();
  
      if (!m_frame) throw std::runtime_error("Unable to allocate frame.");
  
  
  
      m_frame->format = m_context->pix_fmt;
  
      m_frame->width = m_context->width;
  
      m_frame->height = m_context->height;
  
      m_frame->pts = 0;
  
  
  
      ret = av_frame_get_buffer(m_frame, 24);
  
      if (ret < 0) throw std::runtime_error("Unable to allocate frame buffer.");
  
  }
  
  
  
  void VideoTarget::addFrame(QImage &image)
  
  {
  
      // Ensure frame data is writable
  
      int ret = av_frame_make_writable(m_frame);
  
      if (ret < 0) throw std::runtime_error("Unable to make frame writable.");
  
  
  
      // Prepare image
  
      for (int y = 0; y < m_context->height; y++) {
  
          for (int x = 0; x < m_context->width; x++) {
  
              auto pixel = image.pixelColor(x, y);
  
              int pos = (y * 1024 + x) * 3;
  
              m_frame->data[0][pos] = pixel.red();
  
              m_frame->data[0][pos + 1] = pixel.green();
  
              m_frame->data[0][pos + 2] = pixel.blue();
  
          }
  
      }
  
  
  
      m_frame->pts++;
  
  
  
      // Send the frame
  
      ret = avcodec_send_frame(m_context, m_frame);
  
      if (ret < 0) throw std::runtime_error("Unable to send AV frame.");
  
  
  
      while (ret >= 0) {
  
          ret = avcodec_receive_packet(m_context, m_packet);
  
          if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
  
              return;
  
          else if (ret < 0) throw std::runtime_error("Error during encoding.");
  
  
  
          m_target.write((const char*)m_packet->data, m_packet->size);
  
          av_packet_unref(m_packet);
  
      }
  
  }
  
  
  
  VideoTarget::~VideoTarget()
  
  {
  
      int ret = avcodec_send_frame(m_context, nullptr);
  
      if (ret < 0) throw std::runtime_error("Unable to send AV null frame.");
  
  
  
      while (ret >= 0) {
  
          ret = avcodec_receive_packet(m_context, m_packet);
  
          if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
  
              return;
  
          else if (ret < 0) throw std::runtime_error("Error during encoding.");
  
  
  
          m_target.write((const char*)m_packet->data, m_packet->size);
  
          av_packet_unref(m_packet);
  
      }
  
  
  
      // Magic number at the end of the file
  
      uint8_t endcode[] = { 0, 0, 1, 0xb7 };
  
      m_target.write((const char*)endcode, sizeof(endcode));
  
      m_target.close();
  
  
  
      // Free codec stuff
  
      avcodec_free_context(&m_context);
  
      av_frame_free(&m_frame);
  
      av_packet_free(&m_packet);
  
  }

  When used, the class seems to work, and data is written to the file, except I am unable to play back the resulting file in any application.

  My main suspect is these lines :

      // Prepare image
  
      for (int y = 0; y < m_context->height; y++) {
  
          for (int x = 0; x < m_context->width; x++) {
  
              auto pixel = image.pixelColor(x, y);
  
              int pos = (y * 1024 + x) * 3;
  
              m_frame->data[0][pos] = pixel.red();
  
              m_frame->data[0][pos + 1] = pixel.green();
  
              m_frame->data[0][pos + 2] = pixel.blue();
  
          }
  
      }

  The libavcodec documentation was extremely vague regarding the layout of image data, so I effectively had to guess and be happy with the first thing that didn’t crash, so chances are I’m writing this incorrectly. There’s also the issue of size mismatch between my pixel color data calls (giving int values) and the 24-bits-per-pixel RGB format I have selected.

  How do I tweak this code to output actual, functioning video files ?

• avfilter/graphparser : allow specifying filter@id as filter instance

  17 mai 2017, par Muhammad Faiz

  avfilter/graphparser : allow specifying filter@id as filter instance
  See http://lists.ffmpeg.org/pipermail/ffmpeg-user/2017-April/035975.html
  
  Parsed_filter_X could remain and user can override it with custom one.
  Example :
  
  ffplay -f lavfi "nullsrc=s=640x360,
  
  sendcmd='1 drawtext@top reinit text=Hello ; 2 drawtext@bottom reinit text=World',
  
  drawtext@top=x=16:y=16:fontsize=20:fontcolor=Red:text='',
  
  drawtext@bottom=x=16:y=340:fontsize=16:fontcolor=Blue:text=''"
  Reviewed-by : Paul B Mahol <onemda@gmail.com>
  
  Signed-off-by : Muhammad Faiz <mfcc64@gmail.com>
  

  • [DH] doc/filters.texi
  • [DH] libavfilter/graphparser.c

• unable to successfully close ffmpeg stream in node.js

  25 septembre 2022, par K. Russell Smith

  i'm trying to write a node video app that generates frames using the canvas api (via node-canvas, the project's only npm dependancy right now), and writes it to ffmpeg via a stream to generate a video :

  


  const { createCanvas } = require('canvas');
const { spawn } = require('child_process');
const fs = require('fs');
const canvas = createCanvas(1280, 720);

const ffmpeg = spawn('ffmpeg', [
    '-y',
    '-f', 'rawVideo',
    '-vcodec', 'rawVideo',
    '-pix_fmt', 'rgb24',
    '-s', `${ canvas.width }x${ canvas.height }`,
    '-r', '40',
    '-i', '-', '-f', 'mp4',
    '-q:v', '5',
    '-an', '-vcodec', 'mpeg4', 'output.mp4',
]);

const ctx = canvas.getContext('2d');
ctx.font = '30px Prime';
ctx.fillStyle = 'blue';
ctx.textAlign = 'center';
ctx.textBaseline = 'middle';
ctx.fillText('Hello Canvas', canvas.width / 2, canvas.height / 2);

for (let i = 0; i < 250; ++i)
{
    console.log(i);
    ffmpeg.stdin.write(Buffer.from(ctx.getImageData(0, 0, canvas.width, canvas.height).data));
}
ffmpeg.stdin.end();


  


  unfortunately, when i run it, the program throws this after writing the frames :

  


  node:events:368
      throw er; // Unhandled 'error' event
      ^

Error: write EPIPE
    at WriteWrap.onWriteComplete [as oncomplete] (node:internal/stream_base_commons:98:16)
Emitted 'error' event on Socket instance at:
    at emitErrorNT (node:internal/streams/destroy:164:8)
    at emitErrorCloseNT (node:internal/streams/destroy:129:3)
    at processTicksAndRejections (node:internal/process/task_queues:83:21) {
  errno: -32,
  code: 'EPIPE',
  syscall: 'write'
}

Node.js v17.1.0


  


  what am i doing wrong ?