If you were dealing with going from 640x480->720x480 in square pixels, it would look fatter than usual. But since DVD works with non-square pixels, you have to compensate, and resize from that square pixel resolution (640x480 for 4:3, 848x480 or thereabouts for 16:9) to 720x480, and then set the according aspect flag. On a computer monitor it will look correct (unless there was something wonky going on, like I noted with the circles/ovals thing). The reason for seemingly going for both 640x480 and 720x480 is that 640x480 is 4:3, and it's also in square pixels. The -aspect 4:3 flag tells the playback software/hardware to interpret 720x480 as if it were 4:3 - in other words, on a computer it would resize it on playback to either 640x480 or 720x544 (mod16 again for playback only it means less, so it could show up as the actual 720x540 instead). Yes, you want the 4:3, because DVDs don't allow for square pixel resolutions. If it's starting to look like an oval, there's distortion happening. An easy way of telling whether this is the case is to find something in the image that you know is supposed to be a circle (the moon is a really easy one if it's there, but any sort of circle works) - if it's still a circle, you're good. This is all assuming the ratio of the original was correct. If the width is less than 640, then you'd either pillarbox it again slightly, or crop the excess off the height after resizing it proportionally to 640 width.
Or you could crop the excess so it's exactly 640x480. If the width is larger than 640, then you can proportionally scale the width to 640 and just letterbox the remaining height. To crop to actual 4:3, you'd actually want 960x720.īasically, to make it look right, you'd crop off whatever is on the sides, proportionally scale the result down to 480 pixels in height, and then it can get a little hairy if it doesn't scale to exactly 640x480. 1080 is to 720 as 720 is to 480, so that was where the 1080 comes from.It's true, of course, that 1080x720 is the same ratio as 720x480, but on a DVD there's a disconnect between stored resolution and actual aspect ratio, regardless of being 16:9 or 4:3. My original approach was to crop off enough of the left and right so that the video had the correct proportions, and then scale it down. What I want to do is take the 1280x720 16:9 input file, and transfer it down to a DVD-compatible format by trimming off the black bars on the left and right side. What exactly does the "-aspect 4:3" do, and do I need it for (non 16:9) DVD-compatible encoding? Will things play back appropriately if it isn't set? I guess I'm not sure if I want/need the 4:3 or not. Stupidly of me, I didn't realize that 720x480 wasn't 4:3. Changing the -vf to be before the -i flag doesn't seem to change anything.) (Looking at the logging output, it seems that for some reason it's doing a 1280x720->720x480 rescaling, then doing the -vf scale and crop.
(As an aside, where does the 848 in your example command come from?) The crop-then-scale approach was so the scaler was dealing with small, whole number ratios, hopefully lessening scaling artifacts.
1080 is to 720 as 720 is to 480, so that was where the 1080 comes from. (With the version of ffmpeg installed on my computer, which is listed as 0.8.3, copyright Libav developers)
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