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View Full Version : Video size confusion???


go4saket
20th November 2007, 12:30
Hi Guys!

As per my knowledge, a normal CRT TV has 640x480 Pixels. Now, when I watch a video that is smaller, say 320x240 pixels or larger, say 800x600 pixels, how is it that the whole TV screen is properly covered as if the real picture is 640x480 pixels. Does this mean that the player re-encodes the whole video on the fly. If this is the case, I am sure there would surely be a degradation in quality.

Moreover, as I convert my home shooted videos into XVID format using AGK, how mush MB of space should I allot to per minute of video for a good quality outpur. Should I keep it in fixed aspect ratio of 640x480 or should I keep it in auto.

Please help.

Thank you.

burfadel
20th November 2007, 13:14
I thought for NTSC the resolution was 720x480 and for PAL 720x576?

go4saket
20th November 2007, 14:31
That is for DVD and what I am talking about is the native resolution of a TV.

Brother John
20th November 2007, 15:03
An analog TV doesn’t have a native resolution that can be measured in pixels. A TV has a certain amount of discrete lines (vertical res). Horizontally it’s just an analog waveform without any clear discrete division.

The usual corresponding square pixel (btw, DVD pixels are not square) digital resolutions for an SD TV are 768×576 (PAL) and 640×480 (NTSC)*. What your player does is decode the digital signal and then transform it into an analog signal that the TV can understand. Some lossy resizing might be involved, but you’ll never be able to spot any difference. However, there’s never any “re-encoding on the fly” going on.

* Let’s ignore ITU-R BT.601 for simplicity’s sake.

Zach
21st November 2007, 01:31
The usual corresponding square pixel (btw, DVD pixels are not square) digital resolutions for an SD TV are 768×576 (PAL) and 640×480 (NTSC)*.

<...>

* Let’s ignore ITU-R BT.601 for simplicity’s sake.

Whoa... hang on there. I have never heard of 640x480 being cited as a valid resolution under any NTSC DVD specification. Where are you getting that from?

720 x 480 (Full-D1)
352 x 480 (Half-D1)
352 x 240 (VCD standard)
etc.

Edit: For instance, my DVR records everything at 704x480. NTSC DVDs are always 720x480. So again, where are you getting this 640x480 from? I'm just curious.

Brother John
21st November 2007, 01:58
Read again! I wasn’t talking about DVD. I was talking about corresponding square pixel resolutions.