framewright

A drop-in replacement for cv::VideoCapture and cv::VideoWriter that gives you frame-precise seeking, color space control, HDR10 writing, and lossless encoding.

What framewright adds over OpenCV

Reading

Feature	OpenCV	framewright
Frame-precise seeking	Forward only, not frame-accurate	Forward and backward, keyframe-accelerated
Color space control	Opaque, implementation-defined	Explicit BT.709/BT.601 selection, full/limited range override
Color metadata	Not exposed	getColorSpace(), getColorRange(), getPixelFormat(), getCodecID()
Zero-copy frames	No	readRef() avoids per-frame clone
Untagged content	Implementation-defined matrix	Sensible defaults (BT.709 for HD, BT.601 for SD)

Writing

Feature	OpenCV	framewright
HDR10 output	Not supported	HEVC 10-bit with BT.2020, PQ, mastering display metadata
Lossless encoding	Not supported	FFV1 (RGB, no YUV loss), H.264 qp=0 with 4:4:4
10-bit SDR	Not supported	HEVC Main10 with BT.709 for high-precision intermediates
Color space control	Opaque	Explicit BT.709/BT.2020, full/limited range
QuickTime compatibility	Varies	hvc1 codec tag for Safari/QuickTime HDR playback

Verified accuracy

Measured by reading BT.709-tagged lossless test videos with both libraries (OpenCV 4.13.0 and framewright on macOS). Both produce identical pixel values when metadata is present — framewright adds control, not a different answer:

cmake -B build -DFRAMEWRIGHT_BUILD_EXAMPLES=ON && cmake --build build
./build/compare_readers your_video.mp4

Migrating from OpenCV

framewright is a drop-in replacement. The API follows the same conventions (BGR cv::Mat frames):

Reading

// OpenCV
cv::VideoCapture cap("video.mp4");
cv::Mat frame;
cap.read(frame);

// framewright — same API, more capabilities
framewright::VideoReader reader;
reader.open("video.mp4");
cv::Mat frame;
reader.read(frame);

// seek backward (not possible with cv::VideoCapture)
reader.seek(0);
reader.read(frame);

// inspect color metadata
std::cout << "Color space: " << reader.getColorSpace() << std::endl;
std::cout << "Pixel format: " << av_get_pix_fmt_name(reader.getPixelFormat()) << std::endl;

Writing

// OpenCV
cv::VideoWriter w("out.mp4",
    cv::VideoWriter::fourcc('a','v','c','1'),
    30, cv::Size(1920, 1080));
w.write(frame);

// framewright — same pattern, more control
framewright::VideoWriter w;
w.open("out.mp4", AV_CODEC_ID_H264, 1920, 1080, {30, 1});
w.write(frame);
w.release();

Property mapping

OpenCV	framewright
cap.get(CAP_PROP_FRAME_WIDTH)	reader.getWidth()
cap.get(CAP_PROP_FRAME_HEIGHT)	reader.getHeight()
cap.get(CAP_PROP_FPS)	reader.getFPS()
cap.get(CAP_PROP_FRAME_COUNT)	reader.getFrameCount()
cap.get(CAP_PROP_POS_FRAMES)	reader.getCurrentFrameNumber()

Quick start

C++

#include <framewright/framewright.h>

// Read with correct BT.709 color conversion
framewright::VideoReader reader;
reader.open("input.mp4", /*force_bt709=*/true);

cv::Mat frame;
while (reader.read(frame)) {
    // frame is BGR cv::Mat with correct pixel values
}

// Write HDR10 HEVC
framewright::VideoWriterOptions opts;
opts.pix_fmt = AV_PIX_FMT_YUV420P10LE;
opts.is_10bit = true;

framewright::VideoWriter writer;
writer.open("output.mp4", AV_CODEC_ID_HEVC, 3840, 2160,
            {60000, 1001}, opts);  // 59.94 fps
writer.write(hdr_frame);  // CV_16UC3 BGR
writer.release();

Python

import framewright

reader = framewright.VideoReader()
reader.open("input.mp4", force_bt709=True)
for frame in reader:  # numpy (H, W, 3) uint8 BGR
    print(frame.shape, frame.dtype)

writer = framewright.VideoWriter()
writer.open("output.mp4", codec="h264", width=1920, height=1080, fps=30)
writer.write(frame)
writer.release()

Building

As a dependency (CMake FetchContent)

include(FetchContent)
FetchContent_Declare(
    framewright
    GIT_REPOSITORY https://github.com/kmatzen/framewright.git
    GIT_TAG main
)
FetchContent_MakeAvailable(framewright)

target_link_libraries(your_target PRIVATE framewright::framewright)

Standalone

mkdir build && cd build
cmake .. -DFRAMEWRIGHT_BUILD_EXAMPLES=ON
make -j$(nproc)

Python

pip install framewright

Requirements

• C++17 compiler
• OpenCV 4.0+
• FFmpeg 4.2+ (libavformat, libavcodec, libswscale, libavutil)

Logging

By default, framewright only logs errors. To see informational output:

framewright::setLogLevel(framewright::LogLevel::Info);     // See everything
framewright::setLogLevel(framewright::LogLevel::Error);    // Errors only (default)
framewright::setLogLevel(framewright::LogLevel::Quiet);    // Silence all output

API

framewright::VideoReader

Method	Description
open(filename, force_bt709, force_full_range)	Open a video file with optional color space overrides
read(frame)	Read the next frame as BGR cv::Mat (cloned, always safe)
readRef(frame)	Read the next frame without copying (valid until next read)
seek(frame_number)	Seek to a frame (forward and backward)
getPixelFormat(), getCodecID()	Source format info
getColorSpace(), getColorRange()	Color metadata
getFPS(), getWidth(), getHeight()	Video properties

framewright::VideoWriter

Method	Description
open(filename, codec_id, w, h, fps, opts)	Open output with full codec control
write(frame)	Write a BGR frame (CV_8UC3 or CV_16UC3)
setHDR10Metadata(metadata)	Set mastering display / content light level
release()	Flush and finalize the file

framewright::VideoWriterOptions

Field	Default	Description
bitrate	25000000	Target bitrate in bits/sec
pix_fmt	YUV420P	Output pixel format
is_10bit	false	HDR10 mode (BT.2020 + PQ)
full_range	false	Full range (0-255) vs limited (16-235)
use_444	false	4:4:4 chroma (no subsampling)
lossless	false	Mathematically lossless encoding

Supported codecs: H.264, H.265/HEVC (8-bit and 10-bit), FFV1 (lossless RGB).

License

MIT