The signal degradation caused by successive re-recordings (copying). Freshly recorded material is first generation; one re-recording, or copy, makes the second generation, etc. This was of major concern in analog linear editing but much less so in a digital suite. Non-compressed component DVTRs should provide at least twenty tape generations before any adverse artifacts become noticeable, most likely due to dropouts on the tape. Even better multi-generation results are possible with disk-based systems. These can re-record millions of times without causing dropouts or errors. This means that the number of generations are effectively limitless, which is very useful when building multi-layer video, or movie, effects.
Other possible recording media candidates include solid state memories such as DRAM, which is very reliable over a huge number of read/write cycles; provided the power stays on. Static RAM, such as SD cards, is not suitable as it is not as fast as DRAM and is known to degrade over many read/write cycles.
Besides the limitations of recording, the action of processors such as decoders and coders will make a significant contribution to generation loss. The decode/recode cycles of NTSC and PAL are well known for their limitations. Caution is also needed for digital video compression (coding) systems, including MPEG, DV and JPEG, not to mention the vast number of proprietary variants, as well as the color space conversions that typically occur between computers handling RGB and video equipment using Y,Cr,Cb.