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I have a Sony Alpha A5000 camera, and it has quite limited video recording options. In AVCHD format, there are basically two options: 50i and 25p. I do know the basic difference between these two scan types, interlaced and progressive.

Here comes the main confusion. When I transfer the files from my camera to my desktop, and view the details in Mediainfo, both of them show

Frame rate: 25.00 Scan type: Interlaced

However, the 50i video file shows Scan type, store method: Separated fields, whereas 25p video shows Scan type, store method: Interleaved fields.

The question here is that how these file outputs are different? Is one preferred over the another? Any help is appreciated!

Google Drive links for these files:

https://drive.google.com/file/d/1DrnLUHsSHIwvvz8N_ZBOv5Jgg6SEAq8m/view?usp=sharing https://drive.google.com/file/d/1GDvInvgUQDY7Gl4Pzv89QxalnFZh0bOF/view?usp=sharing

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They're kind of the same thing [not exactly, but kind of…]

Progressive scan imaging starts at the first line & works its way - progressively, i.e. line by line - down the screen, meaning for a 1080p signal it must draw 1080 lines for every frame [25 times a second, in your case].

Interleaved scan uses only half the screen - it only scans each alternate line, so for a 1080i image is only has to send 540 lines. The next frame fills the other half of the lines.

Therefore, interleaving can send two frames in the time progressive takes to send one & using approximately the same data bandwidth to achieve it.

Interleaving is, however, not as sharp as progressive, because half the image has moved on since the frame before.
This allows manufacturers to claim it's actually running at 50fps. It isn't really, it's running a data-saving method of 'pretending' it's running at 50 fps, whilst still only drawing the entire screen at 25fps.

This is how the two are 'kind of' the same thing.

Use 25fps progressive every time over any claimed 'double frame cheat'.

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  • This is how I also understand it. However regardless of selecting 50i or 25p from the camera, Mediainfo says that the video is interlaced. Maybe the information there is incorrect then? I'll be sticking to 25p scanning in the future. :)
    – jte
    Commented Jun 24, 2022 at 18:16
  • The Media info is somewhat confusing/confused. A progressive stream should be just that, one whole frame at a time. When an Interlaced scan is presented, it can be separate, or already interleaved [ie it's presented with the 2 'half' scans already merged into one 'proper' frame. Maybe the camera always does 50i & the change is whether it presents separate 'halves' or interleaved. I can't find any accurate info on this.
    – Tetsujin
    Commented Jun 25, 2022 at 8:14

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