What is an I-Frame Interval?
The number of frames between two consecutive Intra-Frames is referred to as I-Frame Intervals. They are an integral part of video compression techniques. I-Frames, also known as Intra-Frames, act as references for all the information that is required to display a single frame of any digital video content.
The nature of the I-Frame Interval largely determines the video's quality and the compression efficiency recorded. In longer I-Frame Intervals, the file sizes are smaller, but the compression efficiency and video quality are compromised. Shorter I-Frame Intervals, on the other hand, can improve quality but at the cost of larger file sizes. The optimal I-Frame Interval is highly variable and will depend on the content and the intended use of the recorded video.
How Do I-Frame Intervals Work?
In simple terms, I-Frame Interval works by evaluating the frequency at which the video encoder inserts I-Frames into the compression video stream.
Unlike P-Frames or B-Frames, I-Frames are encoded without using any reference to other frames used in the video stream. This is because I-Frames have all the necessary information required for a frame. As such, they basically provide a reset point that the decoder can use to decode the subsequent frames efficiently.
The I-Frame Interval, therefore, is specified directly by the video encoder being used. The encoder makes the decision on when to enter the I-Frame depending on the complexity of the video, the targeted bitrate, and the desired video quality.
Shorter I-Frame intervals result in more I-Frames being inserted into the stream. This results in better quality and large file sizes. Conversely, longer intervals result in fewer I-Frames being inserted. This means that the video quality will be lower, but the file size will also be smaller.
Scope of I-Frame Intervals
The nature of I-Frame Intervals can impact the following aspects of a video stream:
- Quality: I-Frame Intervals directly impact the quality of the compressed video. If the intervals are longer, the quality is lower due to the propagation of compression artifacts across the frames. If the intervals are shorter, the quality is improved.
- Compression Efficiency: The length of I-Frame Intervals determines the compression efficiency of the encoder.
- Encoding Complexity: The frequency of I-Frames can directly influence the encoding complexity. If there are more I-Frames, the need for computational resources will be larger. Therefore, encoding complexity will be more compared to when there are fewer I-Frames.
- Decoding Speed: The frequency of I-Frames can also dictate the speed of the decoding process. If more frames are to be decoded, the speed will definitely be slower.
- Scene Changes: I-Frame Intervals are particularly important in the case of videos where there are significant scene changes or movements. If the I-Frame Interval is too long in such situations, the video quality can suffer due to the propagation of compression artifacts across various frames.
- Bit Rate: The I-Frame Interval impacts the bit rate of the compressed video as longer intervals will result in lower bitrates and vice-versa.