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• ffmpeg library m4a moov atom not found when using custom IOContext

  26 avril 2017, par trigger_death

  I’m currently trying to implement FFmpeg into SFML so I have a wider range of audio files to read from but I get the error [mov,mp4,m4a,3gp,3g2,mj2 @ #] moov atom not found when opening an m4a file. Now this only happens when I use a custom IOContext to read the file instead of opening it from URL. This page here says I’m not supposed to use streams to open m4a files but is an IOContext considered a stream ? Because I have no way to open it as a URL as that’s how SFML works.

  // Explanation of InputStream class
  
  class InputStream {
  
      int64_t getSize()
  
      int64_t read(void* data, int64_t size);
  
      int64_t seek(int64_t position);
  
      int64_t tell(); // Gets the stream position
  
  };
  
  
  
  // Used for IOContext
  
  int read(void* opaque, uint8_t* buf, int buf_size) {
  
      sf::InputStream* stream = (sf::InputStream*)opaque;
  
      return (int)stream->read(buf, buf_size);
  
  }
  
  // Used for IOContext
  
  int64_t seek(void* opaque, int64_t offset, int whence) {
  
      sf::InputStream* stream = (sf::InputStream*)opaque;
  
      switch (whence) {
  
      case SEEK_SET:
  
          break;
  
      case SEEK_CUR:
  
          offset += stream->tell();
  
          break;
  
      case SEEK_END:
  
          offset = stream->getSize() - offset;
  
      }
  
      return (int64_t)stream->seek(offset);
  
  }
  
  
  
  bool open(sf::InputStream& stream) {
  
      AVFormatContext* m_formatContext = NULL;
  
      AVIOContext* m_ioContext = NULL;
  
      uint8_t* m_ioContextBuffer = NULL;
  
      size_t m_ioContextBufferSize = 0;
  
  
  
      av_register_all();
  
      avformat_network_init();
  
      m_formatContext = avformat_alloc_context();
  
  
  
      m_ioContextBuffer = (uint8_t*)av_malloc(m_ioContextBufferSize);
  
      if (!m_ioContextBuffer) {
  
          close();
  
          return false;
  
      }
  
      m_ioContext = avio_alloc_context(
  
          m_ioContextBuffer, m_ioContextBufferSize,
  
          0, &stream, &::read, NULL, &::seek
  
      );
  
      if (!m_ioContext) {
  
          close();
  
          return false;
  
      }
  
      m_formatContext = avformat_alloc_context();
  
      m_formatContext->pb = m_ioContext;
  
  
  
      if (avformat_open_input(&m_formatContext, NULL, NULL, NULL) != 0) {
  
          // FAILS HERE
  
          close();
  
          return false;
  
      }
  
  
  
      //...
  
  
  
      return true;
  
  }

• Decoding the h.264 stream from a COM port

  18 mars, par Peter

  I would like to know if there is a reliable way to decode an H.264 NAL stream coming through a serial port using software.

  


  So far, I have managed to decode a single frame using a python script. In this script, I first write the incoming data to a file, and when the end-of-frame marker 00_00_00_01 appears, I display the frame using ffplay.

  


  import serial
import subprocess
import os
import time

ser = serial.Serial('COM3', 115200, timeout=1)
output_file = "output.264"

# Variable to store the ffplay process
ffplay_process = None

# Open the file for writing in binary mode
with open(output_file, "wb") as file:

    print("Writing bytes to output.264. Waiting for the end-of-frame marker 0x00000001.")

    buffer = bytearray()
    marker = b'\x00\x00\x00\x01'

    try:
        while True:
            if ser.in_waiting:  # If there is data in the buffer
                data = ser.read(ser.in_waiting)  # Read all available bytes
                buffer.extend(data)

                # Check if the end-of-frame marker is in the buffer
                while marker in buffer:
                    index = buffer.index(marker) + len(marker)  # Position after the marker
                    frame = buffer[:index]  # Extract the frame
                    buffer = buffer[index:]  # Keep the remaining data

                    print(f"Frame recorded: {len(frame)} bytes")
                    file.write(frame)  # Write the frame to the file
                    file.flush()  # Force writing to disk

                    # Close the ffplay window if it is already open
                    if ffplay_process and ffplay_process.poll() is None:
                        ffplay_process.terminate()
                        ffplay_process.wait()  # Wait for the process to terminate

                    # Play the recorded frame, reopening the window
                    ffplay_process = subprocess.Popen(["ffplay", "-f", "h264", "-i", output_file])

    except KeyboardInterrupt:
        print("\nRecording stopped.")
    finally:
        # Close the serial port and the ffplay process
        ser.close()


  


  However, each time a new end-of-frame marker is detected, the ffplay window closes and reopens to show the next frame. It will flicker when transferring the video. Is there a way to display the frames in the same window for seamless playback when streaming video ?

  


  Or is there a better approach or software that is more suited for this task ? I do not know where to start, so I will be glad for any hints.

  


• how to encode videos for the web and mobile phones using ffmpeg

  3 février 2012, par Arnar Yngvason

  I'm running a website where users can upload their videos and they are all trancoded to the same format (mp4 a.t.m.). Up until now I've been using zencoder (transcoding as a service). But I want to start transcoding the videos on my own server.

  What I would like to know is :

  • Which formats should I transcode to and which sizes are needed for the videos to play on most mobile phones ?
  • Do I actually need webm ?
  • Which is better : CRF or VRF ?
  • I would like the videos to have the same bitrate/quality as the originals. Can I set a max ?
  • Is there a max bitrate I should not exceed if I want to videos to play everywhere ?

  If someone would be so kind to write down the commands I need and explain how they work and what they do, I would be very thankful :)