Keyframe interval

Keyframe interval, also known as the I-frame interval, is a fundamental concept in video encoding and streaming. It plays a crucial role in determining the quality and size of a video file. 

What is keyframe interval?

A keyframe, in the context of video encoding, is a frame in a video file that can be independently decoded without referring to any other frame. The keyframe interval, therefore, refers to the frequency at which these keyframes are inserted in a video stream.

Think of keyframes as the anchors of your video. They provide a reference point for the frames that follow, until the next keyframe appears. The frames between two keyframes are known as delta frames or interframes. These frames only contain the changes from the previous frame, which helps to reduce the overall file size.

Importance of keyframe interval

The keyframe interval has a significant impact on the quality and size of your video file. A shorter keyframe interval results in a higher quality video, but it also increases the file size. Conversely, a longer keyframe interval reduces the file size but can lead to a decrease in video quality.

Furthermore, the keyframe interval also affects the seekability of a video. Since keyframes are the only frames that can be independently decoded, seeking to a specific point in a video requires decoding from the nearest keyframe. Therefore, a shorter keyframe interval improves the seekability of a video.

Setting the keyframe interval

The optimal keyframe interval depends on the content of the video. For videos with a lot of motion and changes, a shorter keyframe interval is recommended. This ensures that the video maintains a high quality throughout.

On the other hand, for static videos or videos with little motion, a longer keyframe interval can be used without significantly impacting the video quality. This helps to reduce the file size and bandwidth requirements for streaming the video.

Impact on video streaming

The keyframe interval plays a crucial role in video streaming. It affects the viewer's experience in terms of video quality, buffering, and seekability.

For live streaming, a shorter keyframe interval is often used to ensure a high-quality stream. However, this increases the bandwidth requirements and may lead to buffering issues for viewers with slower internet connections.

For video on demand (VOD) services, a longer keyframe interval can be used to reduce the file size and bandwidth requirements. However, this can affect the seekability of the video and may lead to a slight decrease in video quality.