Video Encoder

renderkit.processing.video_encoder.VideoEncoder

Video encoder for creating MP4 files using FFmpeg.

Source code in src/renderkit/processing/video_encoder.py

class VideoEncoder:
    """Video encoder for creating MP4 files using FFmpeg."""

    def __init__(
        self,
        output_path: Path,
        fps: float,
        codec: str = "libx264",
        bitrate: Optional[int] = None,
        quality: Optional[int] = 10,
        macro_block_size: int = 16,
    ) -> None:
        """Initialize video encoder.

        Args:
            output_path: Path to output video file
            fps: Frame rate
            codec: Video codec (FFmpeg name like 'libx264', 'libx265', 'libaom-av1')
            bitrate: Video bitrate in kbps (optional)
            quality: Video quality (0-10), 10 is best (optional, used only if bitrate is None)
            macro_block_size: Macro block size for codec compatibility (default: 16)
                             Frame dimensions will be rounded up to multiples of this value
        """
        self.output_path = output_path.absolute()
        self.fps = fps
        self.codec = codec
        self.bitrate = bitrate
        self.quality = quality
        self.macro_block_size = macro_block_size
        self._writer = None
        self._width: Optional[int] = None
        self._height: Optional[int] = None
        self._adjusted_width: Optional[int] = None
        self._adjusted_height: Optional[int] = None
        self._ffmpeg_report_path: Optional[Path] = None
        self._ffreport_prev: Optional[str] = None
        self._ffreport_set: bool = False

    def _configure_ffmpeg_report(self) -> Optional[Path]:
        """Enable ffmpeg report logging (on by default)."""
        value = os.environ.get("RENDERKIT_FFMPEG_LOG", "1")
        if value.lower() in {"0", "false", "no", "off"}:
            return None
        if value.lower() in {"1", "true", "yes", "on"}:
            stamp = datetime.now().strftime("%Y%m%d-%H%M%S")
            path = Path(tempfile.gettempdir()) / f"renderkit-ffmpeg-{stamp}.log"
        else:
            path = Path(value).expanduser()
        path.parent.mkdir(parents=True, exist_ok=True)

        if "FFREPORT" in os.environ:
            self._ffreport_prev = os.environ["FFREPORT"]
        else:
            self._ffreport_prev = None
        escaped_path = _escape_ffreport_path(path)
        os.environ["FFREPORT"] = f"file={escaped_path}:level=48"
        self._ffreport_set = True
        return path

    def _restore_ffmpeg_report_env(self) -> None:
        if not self._ffreport_set:
            return
        if self._ffreport_prev is None:
            os.environ.pop("FFREPORT", None)
        else:
            os.environ["FFREPORT"] = self._ffreport_prev
        self._ffreport_set = False

    def _read_ffmpeg_report_tail(self, max_lines: int = 80) -> Optional[str]:
        if self._ffmpeg_report_path is None:
            return None
        if not self._ffmpeg_report_path.exists():
            return None
        try:
            content = self._ffmpeg_report_path.read_text(errors="ignore")
        except Exception:
            return None
        lines = [line for line in content.splitlines() if line.strip()]
        if not lines:
            return None
        tail = "\n".join(lines[-max_lines:])
        return f"FFMPEG REPORT (tail) [{self._ffmpeg_report_path}]:\n{tail}"

    @staticmethod
    def _make_divisible(dimension: int, divisor: int = 16) -> int:
        """Round up dimension to be divisible by divisor for codec compatibility.

        Args:
            dimension: Original dimension
            divisor: Divisor (typically 16 for macro block size)

        Returns:
            Dimension rounded up to nearest multiple of divisor
        """
        return ((dimension + divisor - 1) // divisor) * divisor

    def __enter__(self) -> "VideoEncoder":
        """Context manager entry."""
        return self

    def __exit__(self, exc_type, exc_val, exc_tb) -> None:
        """Context manager exit - close video writer."""
        self.close()

    def initialize(self, width: int, height: int) -> None:
        """Initialize the video writer with frame dimensions.

        Args:
            width: Frame width
            height: Frame height

        Raises:
            VideoEncodingError: If encoder cannot be initialized
        """
        self._width = width
        self._height = height

        # Adjust dimensions to be divisible by macro_block_size for codec compatibility
        # This prevents ffmpeg from needing to auto-resize frames.
        self._adjusted_width = self._make_divisible(width, self.macro_block_size)
        self._adjusted_height = self._make_divisible(height, self.macro_block_size)

        if self._adjusted_width != width or self._adjusted_height != height:
            logger.warning(
                f"Frame dimensions adjusted from {width}x{height} to "
                f"{self._adjusted_width}x{self._adjusted_height} for codec compatibility"
            )

        # Ensure output directory exists
        self.output_path.parent.mkdir(parents=True, exist_ok=True)

        # Map UI/OpenCV-style codecs to FFmpeg codecs
        codec_map = {
            "avc1": "libx264",
            "hevc": "libx265",
            "mp4v": "mpeg4",
            "XVID": "mpeg4",
        }
        ffmpeg_codec = codec_map.get(self.codec, self.codec)
        available_encoders = get_available_encoders()
        ffmpeg_codec, fallback_warning = select_available_encoder(ffmpeg_codec, available_encoders)
        if fallback_warning:
            logger.warning(fallback_warning)
        if available_encoders and ffmpeg_codec not in available_encoders:
            available = ", ".join(sorted(available_encoders))
            raise VideoEncodingError(
                f"Requested FFmpeg encoder '{ffmpeg_codec}' is not available. "
                f"Available encoders: {available}"
            )

        ffmpeg_log_level = "warning"
        self._ffmpeg_report_path = self._configure_ffmpeg_report()
        if self._ffmpeg_report_path is not None:
            ffmpeg_log_level = "info"
            logger.info("Logging to file: %s", self._ffmpeg_report_path)

        # Set default FFmpeg parameters for broad compatibility and web optimization
        # -movflags +faststart enables progressive loading for web playback
        # Add explicit SDR color tags for predictable playback across platforms
        ffmpeg_params = [
            "-movflags",
            "+faststart",
            "-color_primaries",
            "bt709",
            "-color_trc",
            "bt709",
            "-colorspace",
            "bt709",
        ]

        bitrate: Optional[str] = None

        # Bitrate takes precedence over quality tuning when provided.
        if self.bitrate is not None:
            bitrate = f"{self.bitrate}k"
            if ffmpeg_codec == "libaom-av1":
                ffmpeg_params.extend(["-cpu-used", "6"])
            logger.debug("%s tuning: bitrate=%s", ffmpeg_codec, bitrate)
        # Codec-specific tuning and quality mapping (used only when bitrate is not provided).
        elif ffmpeg_codec in ["libx264", "libx265"]:
            # Map quality (0-10) to CRF (35-18)
            # 10 -> 18 (Excellent), 0 -> 35 (Low quality)
            # Default to 23 if not specified
            crf = 18 + (10 - self.quality) * 1.7 if self.quality is not None else 23
            ffmpeg_params.extend(["-crf", f"{int(crf)}"])
            logger.debug(f"{ffmpeg_codec} tuning: crf={int(crf)}")

        elif ffmpeg_codec == "libaom-av1":
            # AV1 is extremely slow by default. Use -cpu-used 6 for better speed.
            # Map 0-10 quality to CRF 50-20 (lower is better)
            crf = 20 + (10 - self.quality) * 3 if self.quality is not None else 32
            ffmpeg_params.extend(["-crf", f"{int(crf)}", "-cpu-used", "6"])
            # libaom-av1 needs bitrate=0 to enable CRF mode in FFmpeg
            bitrate = "0"
            logger.debug(f"AV1 tuning: crf={int(crf)}, cpu-used=6")

        elif ffmpeg_codec == "mpeg4":
            # Map quality (0-10) to -q:v (31-2)
            # Higher -q:v is lower quality.
            qv = 2 + (10 - self.quality) * 2.9 if self.quality is not None else 4
            ffmpeg_params.extend(["-q:v", f"{int(qv)}"])
            logger.debug(f"MPEG-4 tuning: q:v={int(qv)}")

        # Apply final FFmpeg parameters
        if self._ffmpeg_report_path is not None:
            ffmpeg_params.extend(["-report", "-loglevel", "info"])
        try:
            self._writer = _RawFfmpegPipeWriter(
                self.output_path,
                self._adjusted_width,
                self._adjusted_height,
                self.fps,
                ffmpeg_codec,
                "rgb24",
                "yuv420p",
                ffmpeg_params,
                ffmpeg_log_level,
                bitrate,
            )
            logger.debug(
                f"Initialized FFmpeg pipe writer: {width}x{height} @ {self.fps}fps, "
                f"codec={ffmpeg_codec}, quality={self.quality}, bitrate={bitrate}, "
                f"params={ffmpeg_params}"
            )
        except RuntimeError as e:
            msg = str(e)
            self._restore_ffmpeg_report_env()
            if "ffmpeg" in msg.lower():
                raise VideoEncodingError(
                    "FFmpeg backend not found. Ensure a bundled FFmpeg is available or ffmpeg is on PATH."
                ) from e
            raise VideoEncodingError(f"Failed to initialize video encoder: {e}") from e
        except Exception as e:
            self._restore_ffmpeg_report_env()
            raise VideoEncodingError(f"Failed to initialize video encoder: {e}") from e

    def write_frame(self, buf: oiio.ImageBuf) -> None:
        """Write an ImageBuf frame to the video."""
        if self._writer is None:
            raise VideoEncodingError("Video encoder not initialized. Call initialize() first.")

        spec = buf.spec()
        if spec.width != self._adjusted_width or spec.height != self._adjusted_height:
            buf = ImageScaler.scale_buf(
                buf,
                width=self._adjusted_width,
                height=self._adjusted_height,
                filter_name="lanczos3",
            )
            spec = buf.spec()

        pixels = buf.get_pixels(oiio.FLOAT)
        if pixels is None or pixels.size == 0:
            raise VideoEncodingError("Failed to extract pixel data from ImageBuf.")
        if pixels.ndim == 1:
            frame = pixels.reshape((spec.height, spec.width, spec.nchannels))
        else:
            frame = pixels

        frame_f32 = frame.astype(np.float32, copy=False)
        frame = np.clip(frame_f32, 0.0, 1.0)
        frame = (frame * np.float32(255.0)).astype(np.uint8)

        # FFmpeg rawvideo expects RGB (standard)
        # If RGBA, drop alpha channel
        if len(frame.shape) == 3 and frame.shape[2] == 4:
            frame = frame[:, :, :3]
        elif len(frame.shape) == 3 and frame.shape[2] == 1:
            frame = np.repeat(frame, 3, axis=2)
        # If Grayscale, ensure 3D
        elif len(frame.shape) == 2:
            frame = np.stack([frame] * 3, axis=-1)

        try:
            self._writer.append_data(frame)
        except Exception as e:
            report_tail = self._read_ffmpeg_report_tail()
            if report_tail:
                raise VideoEncodingError(
                    f"Failed to write frame to video: {e}\n\n{report_tail}"
                ) from e
            raise VideoEncodingError(f"Failed to write frame to video: {e}") from e

    def close(self) -> None:
        """Close the video writer."""
        if self._writer is not None:
            try:
                self._writer.close()
                logger.info("Video encoding completed.")
            except Exception as e:
                logger.error(f"Error closing video writer: {e}")
            finally:
                self._writer = None
        self._restore_ffmpeg_report_env()

    def is_initialized(self) -> bool:
        """Check if encoder is initialized."""
        return self._writer is not None

__enter__()

Context manager entry.

Source code in src/renderkit/processing/video_encoder.py

def __enter__(self) -> "VideoEncoder":
    """Context manager entry."""
    return self

__exit__(exc_type, exc_val, exc_tb)

Context manager exit - close video writer.

Source code in src/renderkit/processing/video_encoder.py

def __exit__(self, exc_type, exc_val, exc_tb) -> None:
    """Context manager exit - close video writer."""
    self.close()

__init__(output_path, fps, codec='libx264', bitrate=None, quality=10, macro_block_size=16)

Initialize video encoder.

Parameters:

Name	Type	Description	Default
output_path	Path	Path to output video file	required
fps	float	Frame rate	required
codec	str	Video codec (FFmpeg name like 'libx264', 'libx265', 'libaom-av1')	'libx264'
bitrate	Optional[int]	Video bitrate in kbps (optional)	None
quality	Optional[int]	Video quality (0-10), 10 is best (optional, used only if bitrate is None)	10
macro_block_size	int	Macro block size for codec compatibility (default: 16) Frame dimensions will be rounded up to multiples of this value	16

Source code in src/renderkit/processing/video_encoder.py

def __init__(
    self,
    output_path: Path,
    fps: float,
    codec: str = "libx264",
    bitrate: Optional[int] = None,
    quality: Optional[int] = 10,
    macro_block_size: int = 16,
) -> None:
    """Initialize video encoder.

    Args:
        output_path: Path to output video file
        fps: Frame rate
        codec: Video codec (FFmpeg name like 'libx264', 'libx265', 'libaom-av1')
        bitrate: Video bitrate in kbps (optional)
        quality: Video quality (0-10), 10 is best (optional, used only if bitrate is None)
        macro_block_size: Macro block size for codec compatibility (default: 16)
                         Frame dimensions will be rounded up to multiples of this value
    """
    self.output_path = output_path.absolute()
    self.fps = fps
    self.codec = codec
    self.bitrate = bitrate
    self.quality = quality
    self.macro_block_size = macro_block_size
    self._writer = None
    self._width: Optional[int] = None
    self._height: Optional[int] = None
    self._adjusted_width: Optional[int] = None
    self._adjusted_height: Optional[int] = None
    self._ffmpeg_report_path: Optional[Path] = None
    self._ffreport_prev: Optional[str] = None
    self._ffreport_set: bool = False

close()

Close the video writer.

Source code in src/renderkit/processing/video_encoder.py

def close(self) -> None:
    """Close the video writer."""
    if self._writer is not None:
        try:
            self._writer.close()
            logger.info("Video encoding completed.")
        except Exception as e:
            logger.error(f"Error closing video writer: {e}")
        finally:
            self._writer = None
    self._restore_ffmpeg_report_env()

initialize(width, height)

Initialize the video writer with frame dimensions.

Parameters:

Name	Type	Description	Default
width	int	Frame width	required
height	int	Frame height	required

Raises:

Type	Description
VideoEncodingError	If encoder cannot be initialized

Source code in src/renderkit/processing/video_encoder.py

def initialize(self, width: int, height: int) -> None:
    """Initialize the video writer with frame dimensions.

    Args:
        width: Frame width
        height: Frame height

    Raises:
        VideoEncodingError: If encoder cannot be initialized
    """
    self._width = width
    self._height = height

    # Adjust dimensions to be divisible by macro_block_size for codec compatibility
    # This prevents ffmpeg from needing to auto-resize frames.
    self._adjusted_width = self._make_divisible(width, self.macro_block_size)
    self._adjusted_height = self._make_divisible(height, self.macro_block_size)

    if self._adjusted_width != width or self._adjusted_height != height:
        logger.warning(
            f"Frame dimensions adjusted from {width}x{height} to "
            f"{self._adjusted_width}x{self._adjusted_height} for codec compatibility"
        )

    # Ensure output directory exists
    self.output_path.parent.mkdir(parents=True, exist_ok=True)

    # Map UI/OpenCV-style codecs to FFmpeg codecs
    codec_map = {
        "avc1": "libx264",
        "hevc": "libx265",
        "mp4v": "mpeg4",
        "XVID": "mpeg4",
    }
    ffmpeg_codec = codec_map.get(self.codec, self.codec)
    available_encoders = get_available_encoders()
    ffmpeg_codec, fallback_warning = select_available_encoder(ffmpeg_codec, available_encoders)
    if fallback_warning:
        logger.warning(fallback_warning)
    if available_encoders and ffmpeg_codec not in available_encoders:
        available = ", ".join(sorted(available_encoders))
        raise VideoEncodingError(
            f"Requested FFmpeg encoder '{ffmpeg_codec}' is not available. "
            f"Available encoders: {available}"
        )

    ffmpeg_log_level = "warning"
    self._ffmpeg_report_path = self._configure_ffmpeg_report()
    if self._ffmpeg_report_path is not None:
        ffmpeg_log_level = "info"
        logger.info("Logging to file: %s", self._ffmpeg_report_path)

    # Set default FFmpeg parameters for broad compatibility and web optimization
    # -movflags +faststart enables progressive loading for web playback
    # Add explicit SDR color tags for predictable playback across platforms
    ffmpeg_params = [
        "-movflags",
        "+faststart",
        "-color_primaries",
        "bt709",
        "-color_trc",
        "bt709",
        "-colorspace",
        "bt709",
    ]

    bitrate: Optional[str] = None

    # Bitrate takes precedence over quality tuning when provided.
    if self.bitrate is not None:
        bitrate = f"{self.bitrate}k"
        if ffmpeg_codec == "libaom-av1":
            ffmpeg_params.extend(["-cpu-used", "6"])
        logger.debug("%s tuning: bitrate=%s", ffmpeg_codec, bitrate)
    # Codec-specific tuning and quality mapping (used only when bitrate is not provided).
    elif ffmpeg_codec in ["libx264", "libx265"]:
        # Map quality (0-10) to CRF (35-18)
        # 10 -> 18 (Excellent), 0 -> 35 (Low quality)
        # Default to 23 if not specified
        crf = 18 + (10 - self.quality) * 1.7 if self.quality is not None else 23
        ffmpeg_params.extend(["-crf", f"{int(crf)}"])
        logger.debug(f"{ffmpeg_codec} tuning: crf={int(crf)}")

    elif ffmpeg_codec == "libaom-av1":
        # AV1 is extremely slow by default. Use -cpu-used 6 for better speed.
        # Map 0-10 quality to CRF 50-20 (lower is better)
        crf = 20 + (10 - self.quality) * 3 if self.quality is not None else 32
        ffmpeg_params.extend(["-crf", f"{int(crf)}", "-cpu-used", "6"])
        # libaom-av1 needs bitrate=0 to enable CRF mode in FFmpeg
        bitrate = "0"
        logger.debug(f"AV1 tuning: crf={int(crf)}, cpu-used=6")

    elif ffmpeg_codec == "mpeg4":
        # Map quality (0-10) to -q:v (31-2)
        # Higher -q:v is lower quality.
        qv = 2 + (10 - self.quality) * 2.9 if self.quality is not None else 4
        ffmpeg_params.extend(["-q:v", f"{int(qv)}"])
        logger.debug(f"MPEG-4 tuning: q:v={int(qv)}")

    # Apply final FFmpeg parameters
    if self._ffmpeg_report_path is not None:
        ffmpeg_params.extend(["-report", "-loglevel", "info"])
    try:
        self._writer = _RawFfmpegPipeWriter(
            self.output_path,
            self._adjusted_width,
            self._adjusted_height,
            self.fps,
            ffmpeg_codec,
            "rgb24",
            "yuv420p",
            ffmpeg_params,
            ffmpeg_log_level,
            bitrate,
        )
        logger.debug(
            f"Initialized FFmpeg pipe writer: {width}x{height} @ {self.fps}fps, "
            f"codec={ffmpeg_codec}, quality={self.quality}, bitrate={bitrate}, "
            f"params={ffmpeg_params}"
        )
    except RuntimeError as e:
        msg = str(e)
        self._restore_ffmpeg_report_env()
        if "ffmpeg" in msg.lower():
            raise VideoEncodingError(
                "FFmpeg backend not found. Ensure a bundled FFmpeg is available or ffmpeg is on PATH."
            ) from e
        raise VideoEncodingError(f"Failed to initialize video encoder: {e}") from e
    except Exception as e:
        self._restore_ffmpeg_report_env()
        raise VideoEncodingError(f"Failed to initialize video encoder: {e}") from e

is_initialized()

Check if encoder is initialized.

Source code in src/renderkit/processing/video_encoder.py

def is_initialized(self) -> bool:
    """Check if encoder is initialized."""
    return self._writer is not None

write_frame(buf)

Write an ImageBuf frame to the video.

Source code in src/renderkit/processing/video_encoder.py

def write_frame(self, buf: oiio.ImageBuf) -> None:
    """Write an ImageBuf frame to the video."""
    if self._writer is None:
        raise VideoEncodingError("Video encoder not initialized. Call initialize() first.")

    spec = buf.spec()
    if spec.width != self._adjusted_width or spec.height != self._adjusted_height:
        buf = ImageScaler.scale_buf(
            buf,
            width=self._adjusted_width,
            height=self._adjusted_height,
            filter_name="lanczos3",
        )
        spec = buf.spec()

    pixels = buf.get_pixels(oiio.FLOAT)
    if pixels is None or pixels.size == 0:
        raise VideoEncodingError("Failed to extract pixel data from ImageBuf.")
    if pixels.ndim == 1:
        frame = pixels.reshape((spec.height, spec.width, spec.nchannels))
    else:
        frame = pixels

    frame_f32 = frame.astype(np.float32, copy=False)
    frame = np.clip(frame_f32, 0.0, 1.0)
    frame = (frame * np.float32(255.0)).astype(np.uint8)

    # FFmpeg rawvideo expects RGB (standard)
    # If RGBA, drop alpha channel
    if len(frame.shape) == 3 and frame.shape[2] == 4:
        frame = frame[:, :, :3]
    elif len(frame.shape) == 3 and frame.shape[2] == 1:
        frame = np.repeat(frame, 3, axis=2)
    # If Grayscale, ensure 3D
    elif len(frame.shape) == 2:
        frame = np.stack([frame] * 3, axis=-1)

    try:
        self._writer.append_data(frame)
    except Exception as e:
        report_tail = self._read_ffmpeg_report_tail()
        if report_tail:
            raise VideoEncodingError(
                f"Failed to write frame to video: {e}\n\n{report_tail}"
            ) from e
        raise VideoEncodingError(f"Failed to write frame to video: {e}") from e