DV vs Standard Def on an HD handycam?

your question is vague and relies on generalities that have crucial bearing on the comparison you are trying to draw. first, a typical HD cam works strictly with square pixels, for example 1080x1920 HD is a 16:9 aspect image if the individual pixels are 1:1 aspect. So when you switch to SD mode, it generates a 480x640 pixel image that is 4:3 or "full screen". the MPG file means it uses the MPEG2 codec, which is a universal code that WMM or any other video app understands. it does not generate a widescreen image in SD because it is impossible to generate a 16:9 aspect image using square pixels and have the line count be a multiple of 16 needed for MPEG2 coding which uses 16x16 pixel macro blocks. Your DVD cam i would assume records in standard DVD format, which is also MPEG2, but it does not use square pixels. it makes an SD image of 480x720 for both fullscreen and widescreen aspect. this is called anamorphic. on playback the display device sorts out the pixel shape to get the proper presentation. notice that 720 is a multiple of 16, so it works fine with MPEG2 encoding. DV as in miniDV also uses a 480x720 anamorphic pixel frame size but uses the DV codec, which is also a universal codec but it does not use macro blocks and is not as highly compressed as MPEG2. So a miniDV camera will produce far superior video to either your DVD cam or an HD cam dummied down to SD primarily because of the low compression. now here is the rub, a codec that produces superior video on your computer or television is not suitable for youtube programs. the internet streaming process requires video of the highest possible compression so as to minimize buffering delays. so bottom line, quality of the source camera means very little because the requirements of youtube program delivery essentially reduces everything to minimal quality level anyway.

Your question makes no sense.