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• A way to convert bitrate/format of audio files (between upload & storage to S3)

  5 octobre 2011, par Jonathan Coe

  Currently using PHP 5.3.x & Fedora

  Ok. I'll try to keep this simple. I'm working on a tool that allows the upload & storing of audio files on S3 for playback. Essentially, the user uploads a file (currently only allowing mp3 & m4a) to the server, and the file is then pushed to S3 for storage via the PHP SDK for amazon aws.

  The missing link is that I would like to perform a simple bitrate & format conversion of the file prior to uploading the file. (ensuring that all files are 160kbs and .mp3).

  I've looked into ffmpeg, although it seems that the PHP library only allows for reading bitrates and other meta, not for actual conversion.

  Does anyone have any thoughts on the best way to approach this ? Would running a shell_exec() command that performs the conversion be sufficient to do this, or is there a more efficient/better way of doing this ?

  Thanks in advance ! Any help or advice is much appreciated.

• Streaming without Content-Length in response

  29 août 2011, par kain

  I'm using Node.js, Express (and connect), and fluent-ffmpeg.

  We want to stream audio files that are stored on Amazon S3 through http.

  We have all working, except that we would like to add a feature, the on-the-fly conversion of the stream through ffmpeg.

  This is working well, the problem is that some browsers checks in advance before actually getting the file.

  Incoming requests containing the Range header, for which we reply with a 206 with all the info from S3, have a fundamental problem : we need to know in advance the content-length of the file.

  We don't know that since it is going through ffmpeg.

  One solution might be to write out the resulting content-length directly on S3 when storing the file (in a special header), but this means we have to go through the pain of having queues to encode after upload just to know the size for future requests.
  It also means that if we change compressor or preset we have to go through all this over again, so it is not a viable solution.

  We also noticed big differencies in the way Chrome and Safari request the audio tag src, but this may be discussion for another topic.

  Fact is that without a proper content-length header in response everything seems to break or browsers goes in an infinite loop or restart the stream at pleasure.

  Ideas ?

• 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.