In this scenario with an animated file, inter-frame compression would be lossless, because you could recreate the original animation bit for bit with information stored in the key and delta frames.
The four delta frames store only the blocks of pixels that have changed and refer back to the key frame during decompression for the redundant information. During the video, the only regions in the frame that change are the mouth, cigar, and eyes. This is shown in Figure 1, which is a talking head video of the painter shown on the upper left. Key frames and delta frames as deployed by CD-ROM based codecs. The remaining data in each delta frame is also compressed using intra-frame techniques as necessary to meet the target data rate of the file.įigure 1. During encoding, the pixels in delta frames were compared to pixels in previous frames, and redundant information was removed. Key frames stored the complete frame and were compressed only with intra-frame compression. Inter-frame compression is much more efficient than inter-frame compression, so most codecs are optimized to search for and leverage redundant information between frames.Įarly CD-ROM based codecs like Cinepak and Indeo used two types of frames for this operation: key frames and delta frames.
Inter-frame techniques store the static background information once, then store only the changed information in subsequent frames. For example, in a talking head scenario, much of the background remains static. In contrast, inter-frame compression uses redundancies between frames to compress video. The DV codec also uses solely intra-frame compression, as does DVCPRO-HD, which essentially divides each HD frame into four SD DV blocks, all encoded solely via intra-frame compression. For example, Motion-JPEG uses only intra-frame compression, encoding each frame as a separate JPEG image. Intra-frame compression is essentially still image compression applied to video, with each frame compressed without reference to any other. Lossy compression technologies use two types of compression, intra-frame and inter-frame compression. In other words, the more you compress, the more quality you lose. Lossy codecs have one immutable trade-off–the lower the data rate, the less the decompressed file looks (or sounds) like the original. In contrast to lossless codecs, lossy codecs produce a facsimile of the original file upon decompression, but not the original file. There are some lossless video codecs, including the Apple Animation codec and Lagarith codec, but these can’t compress video to data rates low enough for streaming. Lossless codecs, like PKZIP or PNG, reproduce the same exact file as the original upon decompression. There are two kinds of codecs lossless, and lossy. There are codecs for data (PKZIP), still images (JPEG, GIF, PNG), audio (MP3, AAC) and video (Cinepak, MPEG-2, H.264, VP8). Codec BasicsĬodecs are compression technologies and have two components, an encoder to compress the files, and a decoder to decompress. Next we’ll examine how H.264 became the most widely used video codec today, and finish with a quick discussion of audio codecs. First we’ll cover the basics regarding how codecs work, then we’ll examine the different roles performed by various codecs. Though you probably know what a codec is, do you really know codecs? Certainly not as well as you will after reading this article. Many video producers also touch the DVD-ROM and Blu-ray markets, as well as broadcast, and codecs play a role there as well.
From shooting video to editing to encoding our streaming media files for delivery, codecs are involved every step of the way. Executive SummaryĬodecs are the oxygen of the streaming media market no codecs, no streaming media.
#Newest collection of video codecs for mac series#
This is an installment in our ongoing series of " What Is.?" articles, designed to offer definitions, history, and context around significant terms and issues in the online video industry.
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