VP8 Decoder (Run)

This article explains how you can use Transcoder.run to decode VP8 video in an IVF container to a raw YUV video file.

The code snippets in this article are from the dec_vp8_file Python sample.

Source Video

For source we use the foreman_qcif_vp8.ivf file from the AVBlocks Assets repository. After downloading and unzipping you will find foreman_qcif_vp8.ivf in the vid subdirectory.

Code

This code takes a compressed VP8 video file in an IVF container and decodes it to raw YUV 4:2:0 video format.

Initialize AVBlocks

The first step in any AVBlocks application is to initialize the library. This must be done before using any other AVBlocks functionality. Always call Library.shutdown() at the end of the program to clean up resources.

Library.initialize()

# Set license information. Without this AVBlocks runs in Demo mode.
# Library.set_license("<license-string>")

result = decode(input_file, output_file)

Library.shutdown()

sys.exit(0 if result else 2)

Configure Input Socket

The input socket is created from MediaInfo, which reads the VP8/IVF input file and detects the encoded video stream parameters.

def decode(input_file: str, output_file: str) -> bool:
    """Decode VP8/IVF file to YUV."""
    # Transcoder will fail if output exists (by design)
    delete_file(output_file)

    # Create output directory if it doesn't exist
    output_dir = os.path.dirname(output_file)
    if output_dir and not os.path.exists(output_dir):
        os.makedirs(output_dir)

    with MediaInfo() as media_info:
        media_info.inputs[0].file = input_file

        if not media_info.open():
            print_error("MediaInfo open", media_info.error)
            return False

        # Create input socket from media info
        in_socket = MediaSocket.from_media_info(media_info)
        media_info.close()

        # Create output socket
        out_socket = create_output_socket(output_file)

        # Create transcoder
        with Transcoder() as transcoder:
            transcoder.allow_demo_mode = True
            transcoder.inputs.add(in_socket)
            transcoder.outputs.add(out_socket)

            res = transcoder.open()
            print_error("Transcoder open", transcoder.error)
            if not res:
                return False

            res = transcoder.run()
            print_error("Transcoder run", transcoder.error)
            if not res:
                return False

            transcoder.close()

    print(f"Output: {output_file}")
    return True

Configure Output Socket

The output socket writes uncompressed video to the requested YUV file. The sample configures the output video stream as UncompressedVideo with ColorFormat.YUV420.

def create_output_socket(output_file: str) -> MediaSocket:
    """Create output socket for YUV file."""
    vsi = VideoStreamInfo()
    vsi.stream_type = StreamType.UncompressedVideo
    vsi.color_format = ColorFormat.YUV420

    pin = MediaPin()
    pin.stream_info = vsi

    socket = MediaSocket()
    socket.file = output_file
    socket.stream_type = StreamType.UncompressedVideo
    socket.pins.add(pin)

    return socket

Complete Code

Here’s the complete working example that demonstrates VP8 decoding using AVBlocks for Python.

"""
Decode VP8/IVF file to YUV.

This sample decodes a VP8/IVF video file to raw YUV format using AVBlocks.
"""

import os
import sys
import click

from avblocks import (
    Library, Transcoder, MediaInfo, MediaSocket, MediaPin,
    VideoStreamInfo, StreamType, ColorFormat, ErrorFacility
)


def delete_file(filename: str):
    """Delete a file if it exists."""
    try:
        if os.path.exists(filename):
            os.remove(filename)
    except OSError:
        pass


def print_error(action: str, error) -> None:
    """Print error information."""
    if action:
        print(f"{action}: ", end="")

    if error.facility == ErrorFacility.Success:
        print("Success")
        return

    print(f"{error.message or ''}, facility:{error.facility} code:{error.code} hint:{error.hint or ''}")


def create_output_socket(output_file: str) -> MediaSocket:
    """Create output socket for YUV file."""
    vsi = VideoStreamInfo()
    vsi.stream_type = StreamType.UncompressedVideo
    vsi.color_format = ColorFormat.YUV420

    pin = MediaPin()
    pin.stream_info = vsi

    socket = MediaSocket()
    socket.file = output_file
    socket.stream_type = StreamType.UncompressedVideo
    socket.pins.add(pin)

    return socket


def decode(input_file: str, output_file: str) -> bool:
    """Decode VP8/IVF file to YUV."""
    # Transcoder will fail if output exists (by design)
    delete_file(output_file)

    # Create output directory if it doesn't exist
    output_dir = os.path.dirname(output_file)
    if output_dir and not os.path.exists(output_dir):
        os.makedirs(output_dir)

    with MediaInfo() as media_info:
        media_info.inputs[0].file = input_file

        if not media_info.open():
            print_error("MediaInfo open", media_info.error)
            return False

        # Create input socket from media info
        in_socket = MediaSocket.from_media_info(media_info)
        media_info.close()

        # Create output socket
        out_socket = create_output_socket(output_file)

        # Create transcoder
        with Transcoder() as transcoder:
            transcoder.allow_demo_mode = True
            transcoder.inputs.add(in_socket)
            transcoder.outputs.add(out_socket)

            res = transcoder.open()
            print_error("Transcoder open", transcoder.error)
            if not res:
                return False

            res = transcoder.run()
            print_error("Transcoder run", transcoder.error)
            if not res:
                return False

            transcoder.close()

    print(f"Output: {output_file}")
    return True


@click.command()
@click.option('-i', '--input', 'input_file',
              help='Input VP8/IVF file',
              type=click.Path(exists=True))
@click.option('-o', '--output', 'output_file',
              help='Output YUV file',
              type=click.Path())
def main(input_file: str, output_file: str):
    """Decode VP8/IVF file to YUV."""

    # Set default options if not provided
    if not input_file or not output_file:
        script_dir = os.path.dirname(os.path.abspath(__file__))

        if not input_file:
            input_file = os.path.join(script_dir, "../../assets/vid/foreman_qcif_vp8.ivf")
        if not output_file:
            output_file = os.path.join(script_dir, "../../output/dec_vp8_file/foreman_qcif.yuv")

        print("Using default options:")
        print(f"  --input {input_file}")
        print(f"  --output {output_file}")
        print()

    # Validate options
    print(f"--input: {input_file}")
    print(f"--output: {output_file}")

    Library.initialize()

    # Set license information. Without this AVBlocks runs in Demo mode.
    # Library.set_license("<license-string>")

    result = decode(input_file, output_file)

    Library.shutdown()

    sys.exit(0 if result else 2)


if __name__ == '__main__':
    main()

How to Run

See the Python sample for details. The samples are installed as command-line tools when you install the package from the repository root with uv pip install --editable . (see Installation).

Command Line

dec-vp8-file --input <ivf file> --output <yuv file>

Examples

List options:

dec-vp8-file --help
Usage: dec-vp8-file [OPTIONS]

  Decode VP8/IVF file to YUV.

Options:
  -i, --input PATH   Input VP8/IVF file
  -o, --output PATH  Output YUV file
  --help             Show this message and exit.

Decode the input file ./assets/vid/foreman_qcif_vp8.ivf into output file ./output/dec_vp8_file/foreman_qcif.yuv:

# Linux and macOS
mkdir -p ./output/dec_vp8_file

dec-vp8-file \
    --input ./assets/vid/foreman_qcif_vp8.ivf \
    --output ./output/dec_vp8_file/foreman_qcif.yuv

# Windows
New-Item -ItemType Directory -Force -Path ./output/dec_vp8_file

dec-vp8-file `
    --input ./assets/vid/foreman_qcif_vp8.ivf `
    --output ./output/dec_vp8_file/foreman_qcif.yuv