**Lossy compression**: Reducing video quality involves lossy compression, which discards some of the video data to decrease file size, but this process is irreversible, meaning the original quality cannot be restored.
**Bitrate and resolution**: Two main factors affect video file size: bitrate (the amount of data per unit of time) and resolution (the number of pixels per frame).
Reducing either or both can decrease file size.
**Constant Rate Factor (CRF)**: CRF is a quality setting in video compression that balances quality and file size.
A lower CRF value results in a higher quality video, but larger file size, and vice versa.
**H.264 and H.265**: These are two common video compression formats that provide efficient compression.
H.265 is more efficient, resulting in smaller file sizes, but requires more processing power.
**Container formats**: File formats like MP4, AVI, and MOV are containers that hold video and audio data.
Changing the container format can affect file size, but not necessarily video quality.
**GOP (Group of Pictures)**: GOP is a sequence of frames in a video.
Increasing the GOP size can reduce file size, but may affect video quality during fast-motion scenes.
**Keyframes**: Keyframes are frames in a video that serve as reference points for compression.
Increasing the keyframe interval can reduce file size, but may affect video quality during scene changes.
**Audio compression**: Audio compression, such as AAC or MP3, can significantly affect overall file size.
Using a more efficient audio codec or reducing audio quality can decrease file size.
**Chroma subsampling**: This technique reduces color data in video frames to decrease file size.
However, it can affect video quality, especially in scenes with complex colors.
**Quantization**: This is a lossy compression technique that reduces the precision of video data, resulting in a smaller file size, but potential loss of video quality.
**Scale and crop**: Scaling a video down and cropping it to remove unwanted areas can reduce file size while maintaining quality.
**Variable Bitrate (VBR)**: VBR is a compression method that adjusts bitrate based on the complexity of each frame.
This can result in smaller file sizes without sacrificing quality.
**Container format limitations**: Some container formats, like MP4, have limitations on the number of streams, resolution, and bitrate, which can affect compression efficiency.
**Two-pass encoding**: This is a compression method that analyzes the video data in a first pass and then applies compression in a second pass, resulting in more efficient compression.
**Hardware acceleration**: Using hardware acceleration, like GPU acceleration, can significantly speed up video compression and reduce the computational resources required, making it more efficient.