Earlier this February, when age fotostock announced the opening of video for contributors in the Photographer’s blog, we were pleased to see a lively exchange of comments and opinions on one of our video requirements, that clips must be compressed in codec H.264.  We would like to follow up that debate with a little more information about video compression in general and specifically about the required codec and format for age fotostock.  We look forward to your continued comments, questions and feedback.

Why is video compressed?

The main challenge in the development of digital video was the amount of data required to represent a moving image. A digital photograph was only a few MB, but a sequence of 25 or 30 images was much more data to represent and process.  Too much, in fact…

The compression of the image in the video was absolutely necessary for the digital video work process. Without effective compression, the volume of information to process would make it impossible to do things like post video on the web.  The compression must reduce the flow of data from a video in the least destructive way possible. The goal is to compress as much as possible with a minimal loss of quality.

So digital video is compressed to economize on space, whether it’s bandwidth or media, and a codec (compressor/decompressor) does the job of encoding and decoding. By improving the techniques upon which the codec is based, we’re able to transmit higher quality video using the same bandwidth as before, in other words, more bang for your buck.  There are countless codec’s in use today, some of the most common ones are: MPEG4, Photo-JPG, DivX, MPEG-2 and H.264.

What is the advantage of codec H.264?

The H.264 codec reduces the amount of information required to reproduce the input video by recognizing the redundancies in the frames of a clip in a process generically called motion compensation. This process exploits the fact that between frames is the camera or the subject is what is moving therefore in reference to a video file that means that much of the information in one frame is repeated in the next frame, so by removing redundancies the video files reduces the size. A digital video clip compressed with codec H.264 only uses half the space of MPEG-2 to deliver the same quality video. This means you can enjoy HD video without sacrificing speed or performance.

H.264 has become a new standard for high definition video and is set to supersede some of the formats that are commonplace today such as MPEG-2, the standard for DVD video and some types of cable TV and digital broadcast.  The proof is in the use of this codec by some of the giants within the technological and multimedia world such as Apple, Microsoft, Adobe, Canon, etc (and age fotostock, of course!).

Are there any disadvantages to codec H.264?

As we’ve already explained, H.264 is a very efficient codec, able to reduce the bit rate and achieve an excellent quality and compression rates. These characteristics make the codec ideal for HD video which will be distributed on internet.  In addition, nowadays all video-editing programs include the codec, which produces good results during the editing process.

Nonetheless, if you are planning to edit your audiovisual material extensively, such as retouching, subtle color adjustments, or extracting a chroma-key, than you should try to work with the minimal compression possible.   In these cases, consider converting your H.264 compressed file to a codec with almost no compression, such as Apple Pro-Res.  Once you have finished your fine adjustments, you should encode with H.264 in order to send and handle the file.

What is the difference between a codec and a format?

A video format is the type of file used to store the information of a video clip (AVI, MPEG, MOV, WMV, FLV, etc…)  This is comparable to the file formats in images, such as JPG, TIF, GIF; BMP, etc..  Video formats are considered multimedia “containers,” because the format stores all of the information for images, audio, subtitles, etc. for a clip.

This information within the clip must be compressed so that the clip can be easily handled.  In video, the algorithm used to generate the compression is known as the codec (ex. Photo-JPEG, H.264, MPEG, DivX, etc).  For example, a Quicktime file (abbreviation .mov) is a container for information which might be compressed with any of the following codec’s (Photo-JPEG, H.264, etc…).  This differs somewhat from the world of digital imagery, where you can choose to use formats (such as TIFF) that have no compression.  A photo format such as JPEG, on the other hand, always has some level of compression included (you can determine the degree) so it more easily comparable to a digital video format.

So what is Quicktime?

As we already mentioned, Quicktime is a type of “container” file which is capable of storing a high quantity of multimedia information.  Currently, it is the video format most commonly used for multimedia purposes because it is compact and easy to handle and edit.  It is also multi-platform, compatible with Mac, Windows and several version of Unix.  Quicktime allows for an easy synchronization between audio and video and lastly is versatile with a number of additional technologies (3D, Virtual Reality, video-conferencing, etc) that not all video formats can handle.

Since the version 7.0, Quicktime has been implementing the codec H.264, as a standard codec which allows for a good quality of HD file and with lower bit rates, as previously stated.  age fotostock has chosen to work with Quicktime for all of the above reasons, namely because it is a multimedia system which can reproduce and transmit high quality content online.

What should you do if your clips are not in Quicktime (with H.264 codec)?

As we explain in the Road Atlas, you can convert both the codec and the format in the same operation using a software conversion tool. There are numerous convertors; we recommend a free one called Mpeg-Streamclip that you might know of.

Please feel free to write us with any other questions about creating and processing video or about the video submission processes for age fotostock.  If you have a lot of extra time on your hands or you would like to make sure that we didn’t just make this up, check out these additional resources.

Additional Resources on H.264 and Quicktime

H.264/MPEG-4 AVC

H.264 overview

Steve Jobs talking about H.264

H.264 vs MPEG-2 presentation

Quicktime features