Key considerations when selecting a video compression algorithm: Part 3

A comparison between H.264, MJPEG and other common compression schemes for surveillance video


Latency is also an important consideration. In terms of video, latency is the delay between when things happen in real time and when you see it on your monitor. The most common way to test this is to wave your hand in front of the camera and see how long it takes to see it wave on the monitor. Things that affect latency with H.264 include the profile utilized, how a manufacturer has designed the decoder, and the amount of buffer memory allocated for the video. For the same reason YouTube video is "buffered", many decoders try to "smooth" video, which can add 3 to 4 seconds of latency. Latency really doesn't matter too much for viewing recorded video, but too much latency can be unacceptable for live viewing and can make focusing a camera or using a mechanical pan/tilt/zoom camera nearly impossible. Most security professionals are accustomed to minimal latency and most video systems have latency far less than one second.

Last, pay attention to how the video is displayed on your monitor. A 1600x1200 pixel image displayed on an 800x600 monitor will always appear crisper and clearer than if you showed it on a 1600x1200 monitor. That is because the computer will "down-sample" the image to fit it on the screen and down-sampling masks many undesirable compression artifacts, making the live viewing experience better than displaying the image at 1:1. When you need to display the image at 1:1 (like during forensic analysis of video), inadequate compression techniques or sub-standard H.264 compression profiles will not meet your expectations for megapixel video quality.

 

H.264 Profiles Review

All H.264 profiles are not created equal. H.264 profiles define the maximum possible feature set of an H.264 category, but it is up to each manufacturer to decide which features they use in their implementation. Those decisions can greatly impact the video quality and bandwidth performance of any given H.264 encoder.

 

This comparison table shows 27 of 51 identified key features supported by the different H.264 Profiles. Another source which helps to convey the complexity and widely varying implementations of the standard can be found on Wikipedia's H.264 page, where you can see that out of the 13 vendors listed supporting H.264 there are 13 different implementations of the feature set.

 

Comparison chart of H.264 video compression profiles

The message here is simple: there is much more to the term "H.264" than meets the eye. As seen in the above chart there are thousands of different schemes (feature sets) and every one of them can be called H.264 even though the image quality and bandwidth and storage demands will vary greatly with the implemented features. You must know your video compression encoder and design the system accordingly.

Summary Chart for Article Series

The following chart is intended to help you design an optimal IP video surveillance system by highlighting the major differences between the H.264/temporal and MJPEG/frame-based compression schemes for considerations 1 - 7 that we have in this article series. The highlighted regions show the most important areas to take into account when designing for the most robust video surveillance system.

Comparison chart of H.264 and MJPEG video compression formats

 

Summary Recommendations

In the interests of full disclosure it is important to note that IQinVision has a complete line of H.264 and MJPEG cameras so it is not our intention to promote one over the other. We are simply providing a navigational aid through the vast amounts of misinformation in the industry and, we hope, enough information to make the best choice for your application. Just as megapixel cameras are not all things to all people, neither is H.264/temporal video compression. H.264 is a very complex subject and impossible to boil down to simple rules that fit 100 percent of all applications. Nevertheless, the following rules of thumb should help guide you in making better decisions when choosing your compression methodologies:

  • It is all about the environment and the requirement. The application should determine the selection of a video compression scheme. One size does not fit all.
  • The main benefit of H.264 is lower bandwidth and storage under appropriate conditions, which in general are well lit, high-frame-rate (15+ fps) installations with little scene motion (<20%).
  • To maximize H.264 image quality, we recommend the use of the "main profile" compression and that it is set to variable bit rate (VBR)
  • If using H.264, be sure to design the network to handle high bandwidth spikes and select a server with the necessary processing power for handling increased decoding and display loads.
  • Be sure to factor in weather and lighting conditions when calculating bandwidth and storage needs if specifying H.264 compression.
  • Select a non-temporal compression scheme like MJPEG if the camera is on a mobile platform or in a PTZ unit.