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Thread: Shooting 50i vs 25p

  1. Default Shooting 50i vs 25p

    Hi there guys
    My current cam, Canon's Legria HF G10 (PAL) let's you shoot in either 50i or 25p. The end product is to be a blue-rayt which currently doesn't allow you to use 25p, only 25i.
    I've decided to shoot in 50i and then use vegas studio with the 50i template with the "upper field first option". My guess is that you end up with a 50i blue with markers so that the blu-reader can play it in 25p if you want deinterlaced video.
    The results are great image quality, but when played with interpolation I get a lot of unwanted motion (as if the the image stabilization was turned of). On progresive mode, I get somewhat better results but still on pans I get poor quality.
    My guess is that it all has to do with shooting at 25 frames per seconds but what do you think? Would it be better to shoot in 25p? I don't really understand all that about vertical res which apparently is the difference between i and p.
    Thx

  2. Default

    I was a bit confused about your use of the term 25I because I have always understood the number to mean the number of fields or frames. On Wikipedia they have decided this is incorrect - news to me. Anyway, I think that this issue is also what has caused you confusion. I suspect that your camera produces 50I = 50 interlaced fields per second and according to Wikipedia Blue Ray Disc supports 25 interlaced frames per second - in other words what I term 50I. Therefore, your camera already produces a suitable format for BD as you would expect.

    If you encode your video as 50I your BD player can only show it at 25P if it has built in I2P.

    By the sound of it; you may have to use the lower field first option; but I don't know what kind of interpolation you refer to.

  3. #3

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  4. Default

    Quote Originally Posted by tiliam View Post
    I was a bit confused about your use of the term 25I because I have always understood the number to mean the number of fields or frames. On Wikipedia they have decided this is incorrect - news to me. Anyway, I think that this issue is also what has caused you confusion. I suspect that your camera produces 50I = 50 interlaced fields per second and according to Wikipedia Blue Ray Disc supports 25 interlaced frames per second - in other words what I term 50I. Therefore, your camera already produces a suitable format for BD as you would expect.

    If you encode your video as 50I your BD player can only show it at 25P if it has built in I2P.

    By the sound of it; you may have to use the lower field first option; but I don't know what kind of interpolation you refer to.
    50i and 25p are both 25fps. I have confirmed that. Its seem way too complicated to me as when I get my video to blue cant have 25p from a 25p original as blue doesn't support 25p(God knows why) so I don't really know what happens when 25p gets turned into 25i and then again to 25p when you see it in progressive mode in the tv. My guess is that a lot of resolution gets lost in all those processes. Thats why I decided to shot in 50i so I could create 50i a 50i blue, however I think that maybe as Im deinterlacing the video on vegas I might be getting 25p (after deinterlace) and thus again the accursed conversion must be taking place.


  5. Default

    Quote Originally Posted by gargamel9 View Post
    50i and 25p are both 25fps. I have confirmed that.
    I'm sorry to be pedantic; but we have to ensure that we use the correct terminology to avoid misunderstandings. 50I is not 25 fps. 50I is 50 interlaced fields (from different images) per second; this is not the same as 25 progressive frames per second.

    I didn't realise that you are deinterlacing on Vegas. That means that you now have 50P (although not a genuine 50P). If you want to convert 50I to 25I then you would be better off dropping every other even and odd field. However, this "25I" can't possibly be correct because that would mean the whole frame is refreshed only 12.5 times every second which is a very low rate. Blue Ray "25I" must be what I and everyone I've ever known calls 50I.

    Woh! check the '60i vs 24p' vid!
    And this is why going to the cinema will never be the same again.

  6. Default

    Woh! I did just check and recheck and finally determined that my canon doesn't ever record in progressive mode. Both 50i and 25p are stated as interlaced by media info and I have checked frame by frame (eye check) and all those interlaced jagged edges are present in both. Apparently it is a bogus marketing trick or something and it means video is captured at progresive but the file is interlaced (I fail to see the benefit other than stating that the cam can record in progressive while not being true).
    No use capturing in 25p then now I have to find out a good deinterlace solution (better than vegas 11 at the least)

  7. #8

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    Sorry to interrupt your chat guys but I think I need to point out a couple of things. Firstly your Canon camera will shoot at 1080/50i or 1080/25p this is not a bogus marketing trick it's just different. 1080/50i means 50 interlaced fields per second. See THIS EXPLANATION for what the difference is.

    The other misconception you seem to have is that a BluRay disk will only play at 24fps. Have a look at the chart HERE for a list of frame rates.

    I shoot in both interlaced and progressive modes and found Sony Vegas will handle each format perfectly. See EXAMPLE OF INTERLACED FOOTAGE and EXAMPLE OF PROGRESSIVE FOOTAGE.

    I hope this helps you with you issues.
    Last edited by Midnight Blue; 07-02-2012 at 09:38 PM.

  8. #9

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    What factors might should be considered when choosing whether to film either in I or P ?

  9. #10
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    Quote Originally Posted by tiliam View Post
    I'm sorry to be pedantic; but we have to ensure that we use the correct terminology to avoid misunderstandings. 50I is not 25 fps. 50I is 50 interlaced fields (from different images) per second; this is not the same as 25 progressive frames per second.
    But in order to create a complete frame two consecutive fields are needed (although they will be lightly out of sync) which is why we talk of 25fps. If I film on my MiniDV standard definition camcorder, it is recording 50i but everything (Vegas, GSpot etc) shows it as 25f(rames)ps. I cannot edit one field at a time.

    Quote Originally Posted by tiliam View Post
    I didn't realise that you are deinterlacing on Vegas. That means that you now have 50P (although not a genuine 50P).
    Wrong! You will get 25P (though not a genuine 25P)

    There are some suggestions the built in Vegas deinterlacer is not the best in the world. Here's a tutorial showing the effect of using the yadif de-intelaser.

    Sony Vegas Pro - Deinterlacing Tutorial - YouTube
    Tim

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