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Time to First Frame: A Critical Metric for Video Call Experience

Time to First Frame: A Critical Metric for Video Call Experience

In the realm of video conferencing and streaming, “Time to First Frame” (TTFF) holds immense significance as a crucial metric that gauges the user’s initial experience with video content. It represents the time elapsed between initiating a video call and the appearance of the first video frame on the screen. Users often perceive this metric as “latency,” which is pivotal in shaping their overall engagement and satisfaction.

Importance of TTFF

TTFF has a profound impact on user experience in several ways:

  • First Impression and Engagement: A quick TTFF creates a positive first impression, while a slow one may lead to frustration and abandonment. Users expect a seamless and immediate playback experience, and any delay in the appearance of the first frame can negatively affect their engagement.
  • User Abandonment: Studies indicate viewers start abandoning online videos if they don’t load properly within 2 seconds. Users have limited patience when waiting for videos to load, and a prolonged TTFF may cause them to abandon the video altogether, leading to a loss of audience and potential revenue.
  • Perceived Performance: TTFF is a vital determinant of the perceived performance of a video call. Users often equate slow loading times with poor overall performance, even if the subsequent playback is smooth. On the other hand, a quick TTFF can create the impression of high-quality and well-optimized content.

The 2-Second Rule

the 2 second rule

Research has established a critical threshold of 2 seconds for TTFF. If a video call’s connection time exceeds two seconds before playback commences, audiences begin to drop off. Moreover, each additional second of delay results in an approximate 6% incremental loss of viewers.

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Causes of Latency

causes of latency

TTFF is influenced by several factors that contribute to latency in video calls:

  • Capture: Converting live images to digital signals introduces a delay of at least one frame’s duration (e.g., 1/30th of a second for 30fps).
  • Preprocess: Tasks like noise reduction, image stabilization, and color correction add latency as the video frames are modified.
  • Encode: Encoding live video into a compressed internet-ready format introduces latency ranging from milliseconds to an entire frame duration.
  • Transmit: Encoded video transmission to a video distribution system (VDS) incurs latency affected by media bitrate, internet connection quality, and distance to the VDS.
  • Jitter Buffer: To account for variations in network delay, a jitter buffer temporarily stores incoming video packets, introducing a small amount of additional latency.
  • Decode: Decompressing media on various devices adds latency.
  • Post-Process: This step involves applying enhancements or special effects to video frames, further contributing to latency.
  • Render: Displaying the decoded and post-processed video frames on the recipient’s device involves rendering, which is affected by device capabilities and optimization.

Strategies for Improving TTFF

In real-time audio and video communication technology, “instant TTFF” is usually achieved through the following engineering and technical implementations:

DNS Resolution Optimization: When using a player based on the FFmpeg implementation, all DNS resolution requests are obtained by calling the getaddrinfo method, which helps to improve video playback speed.

Video Encoding Technology: The principle of H.264 and the technology of group coding can make the so-called second-opening technology simple. As long as the sender starts sending from the I frame of the latest GOP to the receiver, the receiver can usually decode the complete image and display it immediately.

End-to-End Latency Reduction: Real-time, end-to-end latency within 1 second, the core technology revolves around reducing latency. In audio and video systems, the delay mainly comes from the network layer, that is, the network transmission delay from the device to the server.

Full-Link Technical Solution: On-demand end-to-end generally refers to the full-link technical solution that the video goes through from uploading to playback, involving the main technical modules such as upload SDK, video processing and management, CDN distribution, and on-demand SDK of the final playback end. In each link, many related technical optimizations and iterations of key functions have been made to achieve a “zero-time-consuming” first-frame video experience.

Real-Time Computing and Data Processing: The core of real-time computing includes real-time data acquisition and real-time data computing. The requirements for high performance and concurrency are second-level responses. Combining the open-source computing platform, self-developed SDK, and the real-time computing framework developed by the receiving system, it can realize the second-level response of real-time computing.

Optimizing the Transmission Mechanism: The optimization practice of real-time video calling and live streaming with a first-frame time of less than 400ms involves optimizing the transmission mechanism to achieve ultra-low real-time audio and video latency.

ZEGOCLOUD’s Approach to Latency Reduction

ZEGOCLOUD has invested heavily in optimizing each aspect of the video calling process to minimize TTFF and deliver a superior call experience. Through years of technical refinement, the company has achieved a millisecond-level TTFF probability of 90% in global real-time video calling scenarios.

zegocloud time to first frame

ZEGOCLOUD’s approach involves:

  • Capture & Render: ZEGOCLOUD uses bilinear downsampling for clearer video at the same resolution, saving time in encoding and transmission.
  • Preprocessing: Optimizations include echo cancellation, noise suppression, and low-light enhancement, with algorithms designed for high efficiency.
  • Encode & Decode: ZEGOCLOUD’s proprietary Z264 codec allows lower bitrate transmission without sacrificing quality.
  • Transmit: A custom transport protocol enables precise packet transmission and efficient congestion handling.
  • Jitter Buffer: Time Scale Modification (TSM) technology effectively balances smoothness and latency.
  • Post-Processing: Advanced audio and video optimization algorithms ensure a seamless user experience.


Time to First Frame is a critical metric that significantly impacts user satisfaction and engagement in video calls. By implementing strategies to minimize TTFF, app owners can create a seamless, immersive video experience that fosters user loyalty and drives business success. ZEGOCLOUD’s proven expertise in latency reduction provides a compelling solution for developers seeking to deliver exceptional video call experiences.

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