Video Freeze Rate

Frequent pauses during video playback can make even the best content frustrating to watch. For developers, these interruptions point to deeper video delivery and playback issues.

One metric that helps track and address this problem is video freeze rate.

What Is Video Freeze Rate?

Video freeze rate is a key performance indicator (KPI) used to measure the smoothness and efficiency of video playback. It quantifies the amount of time during which a video fails to render when it should be progressing.

A high rate means frequent stalls and pauses during video playback, negatively impacting user satisfaction. Conversely, a low rate is a great indicator of smooth and mostly stutter-free video playback.

You can apply this metric to any video delivery method, including streamed content and on-device playback.

Though any video-enabled app can benefit from a lower rate, the impact is most apparent when measuring the video quality of real-time communication platforms. Features like live streaming or live video calls are sensitive to freezes because they cannot buffer ahead of time. Even the smallest freeze can result in disrupted conversation, missed information, or a break in audience engagement.

While developers have long used more traditional metrics like buffering ratio and startup time, video freeze rate is a relatively new KPI that became more common alongside live streaming.

The advantage of using it with other metrics is that it offers a more granular view of playback interruptions. It allows developers and platform operators to find issues that might not appear through traditional metrics alone.

It does come with the downside of a lack of widespread standardization. This can cause different measurements for the same test case. However, if the context of when a video is "frozen" or "playing" is standardized within an organization, this issue is resolved.

Calculating Video Freeze Rate

The formula for calculating video freeze rate is:

Video freeze rate = (Sum of video freezing duration per unit time / Total video duration per unit time) × 100%

Although not universal, the traditional unit of measuring this rate is milliseconds/minute.

In this context, a video being "frozen" refers to the cumulative time during which the video playback is paused. Micro stutters and extended freezes count towards the time the video is frozen. In contrast, frame rate drops, skipped frames, jitters, or the like do not count because the video remains playing, even if not optimally.

Microsoft cites an acceptable video freeze rate of 25 milliseconds/minute for a client-side system.

As mentioned, live-streamed video is more sensitive to video freeze. Though there is no standardized threshold for an acceptable rate in live-streamed video, it should ideally be around one percent to have minimal effect on user experience.

It is important to note that most video freezes happen due to network restrictions, and both of these acceptable thresholds are suggested with a bottleneck-free, low-latency network connection.

What Causes Video Freezing? 

Many factors can cause a high rate, with each affecting video quality in different ways. It is important to understand how these issues are connected to video interruptions to pinpoint problems in your system.

Network Conditions

An unstable internet connection is one of the main causes. High latency, low bandwidth, jitter, and packet loss all play a part in hindering the flow of video packets. This forces the player to pause while more content loads. Limitations caused by network conditions do not play a role when video is stored and played back locally.

Device Performance

Using an underpowered device to playback streamed and on-device video results in a high rate. The hitches in the quality scale are determined by how much information is being fed to your device, such as the resolution, bitrate, and codec of the video being played back. These issues usually stem from weak CPUs, insufficient RAM, or thermal throttling.

Video Player Issues

If a video player isn't properly optimized, it can cause several issues, leading to a high rate. An ill-equipped video player causes mishandled rendering, which in turn causes dropped frames and playback interruptions. Decoding issues and mistimed buffer management can also lead to more frozen videos.

Video Bitrate

An unnecessarily high video bitrate can cause bottlenecks in the network bandwidth and device performance. This makes buffering and stuttering more likely. This issue usually stems from constant bitrate video streams.

Storage Issues

If video stored on-device has a high freeze rate, it can be caused by limitations with your storage device. Fragmented disk storage and slow read speeds cause delays in frame retrieval. This results in slower loading speeds, which ultimately causes the played video to have hitches or freezes.

CDN Performance

On the server side, content delivery networks (CDNs) can cause problems that relate to video freezes. Overloaded servers can cause latency in delivering video segments, which worsens at peak traffic hours. The latency of streamed data causes freezes and interruptions.

Best Practices for Lowering Video Freeze Rate

Here are best practices developers can use to reduce freeze rates:

Implementing Adaptive Bitrate Streaming (ABR)

Adaptive bitrate streaming adjusts the video quality based on the current network conditions. When there is a drop in bandwidth, ABR protocols like HLS or MPEG-DASH automatically adjust the resolution and bitrate of a video to circumvent freezes.

Unlike constant bitrate streaming, these protocols segment videos into small chunks, allowing seamless switches in quality levels that ensure smooth playback.

Optimizing Video Encoding

An efficient codec can reduce the data needed to deliver acceptable video quality.

Codecs like H.264, HEVC (H.265), and AV1 compress videos efficiently while keeping high quality. Lowering the amount of data transferred using these codecs decreases the likelihood of buffering or freezing. Choosing the right codec also lessens the processing load on client devices.

Improving Server and CDN Infrastructure

CDNs cache video data geographically closer to end users, reducing latency and improving download speeds. Load balancing across different servers helps distribute traffic efficiently, preventing server overloads.

Proper CDN configuration is key for global or large-scale video platforms to reduce freezing rates.

Optimizing the Video Player

Tuning your video player to maintain a healthy buffer level is important. This means keeping it high enough to absorb minor network inconsistencies without causing excessive memory use.

Features like hardware-accelerated decoding go a long way in improving performance and reducing frame drops as well. Graceful error handling allows playback to recover from packet loss or decoding issues.

Monitoring and Analyzing Playback Metrics

Using Quality of Experience (QoE) monitoring tools like Mux, Conviva, or Bitmovin Analytics enables real-time tracking of playback performance metrics, including this one. These insights help developers identify issues and continuously optimize the viewing experience.

Frequently Asked Questions