Video Stalls

Introduction

When a video stalls it creates a bad experience for viewers.

As a developer, video producer, or content provider, it is critical to understand the frequency and duration of stalls in a video stream in order to help improve the viewer's experience.

Background

A stall becomes obvious when the viewer sees a spinning wheel icon. Typically, this occurs when the buffer has emptied before the current video segment has finished playing, causing playback to be halted until further video segments are loaded in the buffer.

Once the buffer has enough video stored, the video starts playing again. New segments of the video continue to be downloaded, and if chosen by the player based on a manifest file, they are put into the buffer. As long as the download rate keeps pace with the bit rate everything is fine and the playback will continue smoothly. However, if the buffer is drained, playback halts again, and will not continue until the buffer has a sufficient number of video segments to continue.

The Issue

As mentioned above, stalling creates a bad experience for viewers and is one of the worst things that can happen with a video stream.

When streaming using UDP, common with live events, video file transfer is completed over a connectionless transmission model with a minimum of protocol mechanism. This solves some issues but creates others.

With the move to Adjustable Bitrate streaming for Video On Demand (VOD) and using TCP, stalling can be decreased, but developers, video producers, and content providers must be vigilant.

Delivering video smoothly is an investment. It is critical if you want to keep people engaged. Viewers are becoming less tolerant of stalls, and they will give up on viewing a video without much regret. It isn’t only the viewer who misses out when video streaming is poor - it is the developer, video producer, or content provider.

Best Practice Recommendation

The Best Practice Recommendation is to eliminate all video stalling whenever possible.

The Video Optimizer can detect stalls and report summary statistics on the following:

• The frequency of video stalls
• The duration of video stalls

By measuring the frequency and duration of stream stalling, this Video Optimizer test can help you understand the issue and address it.

Video and other types of rich media are on the rise in mobile apps and in the future we plan on offering more guidance on streaming and other video technology in our Mobile Development Best Practices recommendations.