Why Many 30 FPS Videos Are Actually 29.97 FPS

Have you ever noticed that videos labeled as 30 frames per second (FPS) are often actually 29.97 FPS? If so, you're not alone. This seemingly minor discrepancy is deeply rooted in the history of television broadcasting and the technical standards that have been established over the years.

Historical Context

Television Standards: Understanding the roots of this issue begins in the mid-20th century, specifically in the 1950s when color television was introduced in the United States. This new technology needed to maintain compatibility with existing black-and-white broadcasts.

The original frame rate for black-and-white TV was 30 FPS (30 frames per second). However, the transmission rate was 60 fields per second, which was interlaced. The frame rate of 30 FPS was chosen as a compromise that could fit within the available bandwidth without causing issues.

Color Encoding: To incorporate color information while maintaining backward compatibility, the National Television System Committee (NTSC) standard made a small adjustment to the frame rate. The new frame rate of 29.97 FPS was slightly slower, more precisely 29.97002997002997 FPS, to prevent color information from interfering with the existing black-and-white signal. This adaptation ensured that color broadcasts could fit into the same bandwidth without causing technical issues.

Technical Implications

Broadcasting

Broadcasting: During the broadcasting process, video is often transmitted in a way that requires this specific frame rate to ensure proper synchronization and quality. Adhering to the 29.97 FPS standard is crucial for maintaining the quality and compatibility of broadcasts.

Editing and Production

Editing and Production: For video production, particularly for television, it is essential to maintain this frame rate. This ensures that content will play back correctly on devices and systems that adhere to NTSC standards, preventing playback issues related to timing and synchronization.

Modern Usage

Modern Usage: Even though digital video formats have evolved, many systems still support true 30 FPS. However, the legacy of 29.97 FPS persists in broadcasting and streaming contexts to maintain compatibility with historical standards. Thus, when you see videos labeled as 30 FPS, they are often produced at 29.97 FPS to avoid any playback issues related to timing and synchronization.

Note: It is important to note that there are no "partial" frames. The frame rate of 29.97 FPS is just slightly slower than 30 FPS. This discrepancy is due to the historical need to superimpose color information onto a monochrome signal, which has caused some challenges for TV engineers but remains essential for broadcast television.

The transition to color television required creating a frame rate that would fit within the existing bandwidth while maintaining compatibility with black-and-white broadcasts. This decision, made decades ago, has had a lasting impact on modern video production and broadcasting practices.