Compressed data cannot be accessed in the same manner than uncompressed data. The particular contents of a compressed file is commonly depending on preceding or surrounding contents. A direct manipulation is not possible. The only way is to decode the concerned part and to encode it again after the editing had taken place.

This permanent coding expenditure does not only require additional resources, it also leads to losses if procedures with irrelevance reduction were used (MPEG, JPEG, etc.). The resulting compression artefacts will be accumulated by frequent repetition of this cyclus (decoding, editing, encoding). For a system design this is of importance and must be taken into consideration before choosing a compression procedure and/or ratio.

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