H.264 vs MxPEG

April 2014 CCTV, Surveillance & Remote Monitoring

Thanks to Hollywood, H.264 has become the world’s most popular compression codec, used by YouTube, iTunes, Adobe and most of the security industry. One asks, why then does Mobotix stick with its proprietary codec MxPEG when it appears that H.264 is dominating the market?

The answer to this question lies in the purpose for the use of the camera. MxPEG was developed specifically for security applications where detail in each frame of the video is important. Therefore one has the advantage of freezing each image into picture perfect quality, rather than having footage which only looks good whilst it’s playing. The below explanation on the different types of codec used explains this principle.

A codec (enCOder/DECoder) is a standard of how video is compressed (encoded) and then decompressed for viewing (decoded). Commonly known codecs in the industry are M-JPEG, MPEG-2 (used on DVD), MPEG-4, H.254 (used on Blu-Ray and YouTube).

Lossy codecs: Many of the more popular codecs in the software world are lossy, meaning that they reduce quality by some amount in order to achieve compression. Often, this type of compression is virtually indistinguishable from the original uncompressed sound or images, depending on the codec and the settings used. Smaller data sets ease the strain on storage and bandwidth, but do require more processing power on both ends.

Lossless codecs: There are also many lossless codecs which are typically used for archiving data in a compressed form while retaining all of the information present in the original stream. If preserving the original quality of the stream is more important than eliminating the correspondingly larger data sizes, lossless codecs are preferred. This is especially true if the data is to undergo further processing (for example editing) in which case the repeated application of processing (encoding and decoding) on lossy codecs will degrade the quality of the resulting data such that it is no longer identifiable (visually, audibly or both). Using more than one codec or encoding scheme successively can also degrade quality significantly. The decreasing cost of storage capacity and network bandwidth has a tendency to reduce the need for lossy codecs for some media.

Inter-frame compression: This is where a frame in a video compression stream is expressed in terms of one or more neighbouring frames. The 'inter' part of the term refers to the use of inter frame prediction. This kind of prediction tries to take advantage from temporal redundancy between neighbouring frames allowing it to achieve higher compression rates.

Intra-frame compression: This is where various lossless and lossy compression techniques are performed relative to information that is contained only within the current frame, and not relative to any other frame in the video sequence. In other words, no temporal processing is performed outside of the current picture or frame. Non-intra coding techniques are extensions to these basics. It turns out that this block diagram is very similar to that of a JPEG still image video encoder, with only slight implementation detail differences.

Most security cameras nowadays have both H.264 (inter-frame compression) and M-JPEG (intra-frame compression) available.

H.264 is an inter-frame compression which offers good motion video with savings on bit-rate and storage, but in a security application, when the video is frozen on a single frame, there is often lack of detail and sharpness. This becomes increasingly noticeable on high-resolution footage. Inter-frame compression is very CPU hungry and when it is necessary to decode multiple streams, computing power needs to be increased. This is why workstations are normally quite expensive. H.265, H.264’s successor offering higher than 1080p resolution will again require even more processing power.

M-JPEG is an intra-frame compression that offers good detail on each frame but this comes at the cost of storage and bandwidth, yet it is a lot lighter on processing power. Bandwidth is more commonly the biggest bottleneck to take into consideration when designing a solution. M-JPEG is popular for analytics as the detailed frames are crucial for it to work effectively.

MxPEG uses a combination of the two compressions and was designed to be closely related to JPEG. It should add inter-frame compression where motion JPEG only makes use of JPEG’s intra-frame compression. This is done on a tile basis preserving the quality of each frame. This offers reduced bandwidth, storage and processing requirements.

Therefore it is quite evident that while H.264 may be ideal for movies, it has incorrectly been interpreted to be so in the security industry. Despite the fact that the MxPEG does not offer the most efficient compression if large parts of the image are changing, (e.g., when the camera is mounted on a constantly moving PTZ head), this is normally avoided anyway as it is wasted recording. MxPEG does offer the advantage of far better image detail on every frame, which is crucial for security applications. In addition to this, it offers similar savings in bandwidth and storage as H.264 as well as far less processing power requirements. Therefore from a security perspective it is evident that the MxPEG is the better alternative.

For more information, contact Haiko Wöstmann, ProDIS, +27 (0)12 753 4491, haiko@prodis.co.za




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