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| Unofficial VirtualDub Support Forums > Codec Discussion > Interlaced(i) And Progressive(p) Frames |
| Posted by: vishwak1 Feb 8 2010, 09:28 AM |
| I am new into to the codec field.I am currently trying to understand the MPEG-2 compression algorithm.As part of that , first I am trying to understand the entities of how a video is captured and digitized and stored. As part of this process , I came across that a frame is categorized as either I or a P frame. But according to me I think that a frame is Either a I or P frame depending on the way its displayed , rather than the way it is captured.Please help me in this issue and please share all your understandings. |
| Posted by: stephanV Feb 8 2010, 09:41 AM |
| I and P does not stand for interlaced and progressive in this case, but for Intra and Predicted. An I frame can be decoded on its own. A P frame requires frame(s) before it to be decoded. There are also B frames (bi-directional) which are similar to P frames except that can also require frames after to be decoded first. An MPEG2 video stream is typically coded in this order (although it doesn't have to be this way) IBBPBBPBBPBBPBBP IBBPBBPBBPBBPBBP (etc.) |
| Posted by: vishwak1 Feb 8 2010, 10:04 AM |
| Hi stephen , I just used I for Interlaced and P for Progressive as short forms. Going on I will use the complete terminology. My actual question was , When do we categorize a video as Interlaced (or) Progressive , while capturing (or) while displaying ? According to me , Interlaced and Progressive video categorization comes while displaying the video content , depending upon their display methodologies. Please provide ur suggestions.. |
| Posted by: stephanV Feb 8 2010, 11:21 AM |
| At both times. Interlacing/progressive is important to know when the video is stored and when it is displayed. |
| Posted by: vishwak1 Feb 8 2010, 01:02 PM |
| So on what basis we categorize a raw video which is captured to be Interleaved (or) Progressive? Is there any difference the way we capture a Interleaved video (or) Progressive video? |
| Posted by: stephanV Feb 8 2010, 01:25 PM |
| You know on beforehand what you are going to capture. |
| Posted by: fredgiblet Feb 8 2010, 05:44 PM | ||||
From the source, if you are capturing from VHS for instance it's going to be interlaced, if you are capturing from cable it could be either.
Not really, any capturing program should be perfectly capable of capturing either, some codecs (like XviD) offer much better performance with progressive content and have options available to increase performance on interlaced content that should be activated but other than that the procedure is usually identical. |
| Posted by: vishwak1 Feb 10 2010, 12:20 PM |
| So when we capture from the VHS , do we capture all the odd fields first and then the even fields and then combine them to construct a raw frame ?? |
| Posted by: stephanV Feb 10 2010, 12:23 PM |
| The capture card will take an odd and even field and put them in one frame and then goes on to the next odd and even field. |