What is the Keyframe Interval?
Keyframes, also known as I-frames, are frames in a video that contain complete image information and serve as reference points for decoding subsequent frames. In contrast, non-keyframes, also known as P-frames and B-frames, only contain partial image information and rely on information from preceding keyframes and other frames to be decoded.
How Does Keyframe Interval Work?
The keyframe interval setting determines how often a keyframe is inserted in the video stream. A shorter interval means more keyframes will be inserted, resulting in higher-quality video and larger file sizes. A longer interval means fewer keyframes will be inserted, resulting in lower-quality video and smaller file sizes.
The keyframe interval setting is often expressed in terms of the number of frames between keyframes. For example, a keyframe interval of 30 means that a keyframe is inserted every 30 frames.
When a video stream is encoded, the encoder algorithm divides the video into a series of frames and decides which frames should be designated as keyframes. Keyframes are inserted into the video stream at regular intervals according to the keyframe interval setting. When a video is decoded, the decoder algorithm uses the keyframes as reference points to decode the subsequent frames in the video stream.
Factors for Setting The Right Keyframe Interval
To set the right keyframe interval, there are several factors you should consider:
- Video content: The type of content in your video can influence the choice of keyframe interval. For example, if you have a video with fast-moving action, a shorter keyframe interval may be necessary to avoid motion artifacts, whereas for a video with little movement, a longer keyframe interval may be sufficient.
- Bitrate: The bitrate of your video encoding also plays a role in determining the optimal keyframe interval. A higher bitrate can support more frequent keyframes, resulting in the higher-quality video, while a lower bitrate may require a longer keyframe interval to maintain video quality.
- Resolution: The resolution of your video can also affect the choice of keyframe interval. Higher-resolution videos may require more frequent keyframes to avoid visual artifacts, whereas lower-resolution videos may not require as frequent keyframes.
- Playback device: The device on which your video will be played back is also a factor to consider. Different playback devices have different capabilities and requirements and may require different keyframe intervals for optimal playback.
- Encoding complexity: The complexity of your video encoding can also impact the choice of keyframe interval. More complex encoding, such as using multiple reference frames or advanced compression techniques, may allow for longer keyframe intervals without sacrificing video quality.