I have an old SD PAL camcorder, which records on miniDV tapes at a resolution of 720x576 pixels.
This is the output from ffmpeg of the 4:3 recording:
Stream #0:0: Video: dvvideo, yuv420p, 720x576 [SAR 16:15 DAR 4:3], 28800 kb/s, 25 fps, 25 tbr, 25 tbn, 25 tbc
This is the output instead for the 16:9 widescreen footage:
Stream #0:0: Video: dvvideo, yuv420p, 720x576 [SAR 64:45 DAR 16:9], 28800 kb/s, 25 fps, 25 tbr, 25 tbn, 25 tbc
I noticed that the resolution is the same in both the cases, and of course the SAR is different, in one to fit the 4:3 resolution, in the second to fit 16:9. This leads me to think that the footage should be stretched to fit the aspect ratio but keep the same resolution in both cases.
However, the actual video footage is quite different. It doesn't look like they use the same resolution, but more that the 16:9 footage is cropped vertically. This would make sense logically, since the sensor is 4:3. However, shouldn't that mean that the resolution is lower? How is it possible that the footage has the same resolution while recording but a different one while reproducing?
EDIT: To clarify what I mean above, I took a screenshot of both video. As expected, both videos fit the two formats: 768x576 for 4:3 (16:15 stretch), and 1024x576 for 16:9 (64:45 stretch). Which again, is what is expected.
However, the image is evidently cropped vertically in the second case. For example, if I put a ball on the top and the bottom of the screen, it would be visible in 4:3, but would be cut out in 16:9. Video quality is also much lower in this case, as expected from an upscale. It looks like the image is first cropped at something like 720x405, and then upscaled to 1024x576.
I wonder why this happens, instead of having just the image at 720x576 stretched out to 16:9.