Recording the analog output has a lower quality than the original stream for 3 main reasons:
1. Marketing and psychology: Viewers want to believe they are viewing the original, not a degraded copy.
2. Unfaithful copy: Analog output and analog input introduce errors. LCDs use a variety of tricks to improve resolution such as spacial and temporal dithering. Also you can't use a normal camera to record a monitor because of aliasing (of pixels and non-genlocked frame rates).
3. Encoding noise. The encoding of the original is based on the higher quality original, and carefully optimised for the least visual artifacts. Any re-encoding also has to deal with noise introduced by the copying process, and with the noise introduced by the original encoding. This noise noticeably reduces the quality of a copy.
1. Marketing and psychology: Viewers want to believe they are viewing the original, not a degraded copy.
2. Unfaithful copy: Analog output and analog input introduce errors. LCDs use a variety of tricks to improve resolution such as spacial and temporal dithering. Also you can't use a normal camera to record a monitor because of aliasing (of pixels and non-genlocked frame rates).
3. Encoding noise. The encoding of the original is based on the higher quality original, and carefully optimised for the least visual artifacts. Any re-encoding also has to deal with noise introduced by the copying process, and with the noise introduced by the original encoding. This noise noticeably reduces the quality of a copy.