H.264 Compression Delivers More With Less
There’s a new technology on the block in the digital video surveillance world and it’s getting a fair amount of attention. I’m referring to the H.264 compression standard that is starting to show up in the specifications of digital and megapixel cameras and also as the subject of several online articles and blogs.
So what do we know about this new technology? How does it compare to the various MPEG and JPEG compression formats? And, how is it going to affect us?
Lessons in H.264First of all, the H.264 compression standard is not new. It was ratified by the joint MPEG/VCEG (Video Coding Experts Group) committee in 2003 as an extension of MPEG4, and was named MPEG4 Part 10 – although it is more generally known as H.264 AVC (Advanced Video Codec). The new compression algorithm was initially used most commonly in communication applications such as videoconferencing and was then subsequently adopted by the broadcast and computer industries.
Essentially, H.264 compression technology compares a frame of video (R - reference frame) to the preceding coded frame (I - index frame) and then codes only the differences in the R frame. It continues doing this until a new I frame refreshes the scene. Think of a video surveillance camera focused on a gaming table wherein the green felt tabletop does not change but there is movement of the cards and motion by the dealer and the players. The camera would only process the changes in the frame; namely the movement of the cards and the motion of the individuals.
Compare and ContrastAlso common to the MPEG4 format, this technique is known as temporal compression and it significantly reduces the overall amount of data to be compressed, with very little loss of image quality. H.264 is more efficient, however, than MPEG4 in its technique, and the compressed files are somewhat smaller and of higher quality than MPEG4 files.
Another area where H.264 differs significantly from MPEG4 is in video motion processing and the difference is a visually more pleasing image with H.264. As well, H.264’s advanced processing techniques expand the use of the standard to include video surveillance applications, particularly those where more motion may be involved from either the camera itself or from the image subject. The H.264 standard includes predicting capabilities (using past, current and next frames) and enhanced motion compensation that are improved over the MPEG4 standard. Again using the gaming table as our example, the camera processor can intelligently predict movement of the cards to determine which pixels or blocks of pixels are going to be different and code accordingly.
Comparing H.264 to MPEG4 is a little like comparing apples to apples, but comparing H.264 to MJPEG (motion JPEG) is more like comparing apples to oranges. This reason for this is because MJPEG uses a frame by frame compression technique, known as spatial compression. In other words, each frame of video is compressed, independent of the surrounding frames. The compression works by taking advantage of data, which is similar in the frame, such as the green felt tabletop of the gaming table. This data varies little from pixel to pixel and therefore fewer bits need to be coded.
The MJPEG technology was derived from the JPEG compression standard and instead of compressing a single image as a JPEG file, MJPEG compresses 24-30 images per second and stores them in sequence. It is certainly a high quality compression scheme and very fast but it also suffers from problems inherent in the fact that it was originally developed to compress still images. As well, the frame-by-frame compression results in larger files than H.264 or MPEG4 files and consequently requires considerably more bandwidth.
So how will H.264 compression format affect us? As we can see from the explanation of the technology, the H.264 compression scheme reduces the amount of bandwidth required in order to transmit video files. This is momentous, in my opinion, because it takes away the excuse of not having enough bandwidth to implement an IP video surveillance system. Secondly, the reduced file sizes will drastically lower the amount of data that needs to be recorded and/or stored.
H.264 is a welcomed addition to the scene and can only help in continuing to move our industry forward.