1. Analog to Digital Conversion: While DVDs store data in a digital format, copying often involves an analog step. If the source DVD player's analog output is used for copying, the signal is converted to analog, potentially introducing noise and interference that can affect the quality of the copied DVD.
2. Video Compression: DVD video is typically compressed using MPEG-2 compression. Copying often involves re-compressing the video, which can further degrade the quality. The level of degradation depends on the compression algorithm and bit rate used. Higher compression rates, necessary to fit the movie onto a recordable DVD, can result in more noticeable quality loss.
3. Generation Loss: Every time a DVD is copied, there is a loss of quality. This is because even digital copies are not perfect, and some information is lost during the copying process. The more generations removed from the original DVD, the more noticeable the quality degradation becomes.
4. DVD Media Quality: The quality of the blank recordable DVDs used for copying also plays a role. Lower-quality media may have more defects or be less resistant to wear, leading to potential playback issues and accelerated degradation over time.
5. Copy Protection: Some DVDs have copy protection mechanisms that can interfere with the copying process or introduce additional errors, impacting the quality of the copied movie.
6. Interlacing and Deinterlacing: Standard DVDs use interlaced video, which combines two fields to create a single frame. Copying using devices that do not properly handle deinterlacing can result in visible combing artifacts in motion sequences.
7. Up/Down Scaling: If the resolution of the copied DVD is different from the original, it may undergo upscaling or downscaling. This process can introduce additional blurring or aliasing artifacts, affecting the image quality.
In summary, while copying DVDs can be convenient for personal use, it often comes at the cost of reduced movie quality due to various factors related to analog conversions, compression, generation loss, media quality, copy protection, and video processing techniques. To ensure the best possible quality, it is generally advisable to obtain movies through legitimate sources rather than resorting to unauthorized copying.