Post by frayadjacent on Oct 2, 2012 0:03:10 GMT -5
Hi all,
Obsessive24 noticed some aspect ratio issues in my latest vid and offered to help me figure out the source of the problem. We both suspect that the issue is the pixel aspect ratio, but I'm still a bit confused on how all that works. I'm posting on it here so that the thread will be here if people in the future have this problem!
I have lots of screenshots that I can add to this post if need be. I took a screenshot of relevant settings for just about every point in my workflow, but I think it could be overkill to post them.
OK, so my basic workflow follows Elvira's tutorials at Foolish Passion for Final Cut users. I use Mac the Ripper to extract VOB files from DVDs, then use MPEG Streamclip to make clips. I follow this tutorial for clipping, creating .mov files using the DV/DVCPRO NTSC codec.
Now, I know from this thread on non-square pixels that DV/NTSC do not use square pixels because the frame size is required to be 720x480. If the frame aspect ratio is 16:9, that implies a pixel aspect ratio of ~1.2:1. (I.e., a frame that is 720 pixels wide and has 16 pixels on the horizontal for every 9 pixels on the vertical would have a height of 720*9/16 = 405 pixels, if the pixels were square. DV/NTSC accommodates the extra pixels in the vertical by stretching them horizontally.)
So, the clips that I import into Final Cut Express should not have square pixels right? According to Final Cut, my clips have a pixel aspect ratio called "ncst ccir 601". It looks like there is an option to change it to square, but my hunch is I shouldn't do that. My hunch is that, when I export the vid, it is supposed to convert to square pixels and use cropping and/or letterboxing to maintain the frame size.
Here is a screenshot of my export settings, following this tutorial.
As you can see, I'm trying to export a high quality vid, which I'll then convert to a web-ready vid with MPEG streamclip. In the past, I've always chosen "None" for compression, but that option suddenly is no longer available (I guess because I upgraded my operating system?). So instead I chose "Animation", and I also selected the option to preserve aspect ratio using crop. If I don't do this, the image is very visibly stretched. These are the two differences between the tutorial and what I do.
I *think* this is where things go wrong, because the exported file has dimensions of 854x480, but there are black bars on the top and bottom, even though this size frame should match the 16:9 aspect ratio with square pixels (854*9/16=480). There shouldn't be any black bars.
I think the problem is that Final Cut isn't squaring the unsquare pixels on export. I tried instead exporting with a frame size of NTSC 720x480, with the idea that I would then convert in MPEG streamclip (including cropping?), which Foolish Passions says will "magically" square the pixels. The exported 720x480 file looks fine when I open it in Quicktime but looks very *squished* when I open it in MPEG streamclip.
So now I am a little baffled, and would appreciate any help! It would also be great to hear a little more about what looks off about the aspect ratio when people view my vid. I ask because I actually can't see the problem, and I'm not sure if that's because I'm looking at it with players that are correcting the issue somehow or if it's just my untrained eye.
Thanks!
-Fray
Obsessive24 noticed some aspect ratio issues in my latest vid and offered to help me figure out the source of the problem. We both suspect that the issue is the pixel aspect ratio, but I'm still a bit confused on how all that works. I'm posting on it here so that the thread will be here if people in the future have this problem!
I have lots of screenshots that I can add to this post if need be. I took a screenshot of relevant settings for just about every point in my workflow, but I think it could be overkill to post them.
OK, so my basic workflow follows Elvira's tutorials at Foolish Passion for Final Cut users. I use Mac the Ripper to extract VOB files from DVDs, then use MPEG Streamclip to make clips. I follow this tutorial for clipping, creating .mov files using the DV/DVCPRO NTSC codec.
Now, I know from this thread on non-square pixels that DV/NTSC do not use square pixels because the frame size is required to be 720x480. If the frame aspect ratio is 16:9, that implies a pixel aspect ratio of ~1.2:1. (I.e., a frame that is 720 pixels wide and has 16 pixels on the horizontal for every 9 pixels on the vertical would have a height of 720*9/16 = 405 pixels, if the pixels were square. DV/NTSC accommodates the extra pixels in the vertical by stretching them horizontally.)
So, the clips that I import into Final Cut Express should not have square pixels right? According to Final Cut, my clips have a pixel aspect ratio called "ncst ccir 601". It looks like there is an option to change it to square, but my hunch is I shouldn't do that. My hunch is that, when I export the vid, it is supposed to convert to square pixels and use cropping and/or letterboxing to maintain the frame size.
Here is a screenshot of my export settings, following this tutorial.
As you can see, I'm trying to export a high quality vid, which I'll then convert to a web-ready vid with MPEG streamclip. In the past, I've always chosen "None" for compression, but that option suddenly is no longer available (I guess because I upgraded my operating system?). So instead I chose "Animation", and I also selected the option to preserve aspect ratio using crop. If I don't do this, the image is very visibly stretched. These are the two differences between the tutorial and what I do.
I *think* this is where things go wrong, because the exported file has dimensions of 854x480, but there are black bars on the top and bottom, even though this size frame should match the 16:9 aspect ratio with square pixels (854*9/16=480). There shouldn't be any black bars.
I think the problem is that Final Cut isn't squaring the unsquare pixels on export. I tried instead exporting with a frame size of NTSC 720x480, with the idea that I would then convert in MPEG streamclip (including cropping?), which Foolish Passions says will "magically" square the pixels. The exported 720x480 file looks fine when I open it in Quicktime but looks very *squished* when I open it in MPEG streamclip.
So now I am a little baffled, and would appreciate any help! It would also be great to hear a little more about what looks off about the aspect ratio when people view my vid. I ask because I actually can't see the problem, and I'm not sure if that's because I'm looking at it with players that are correcting the issue somehow or if it's just my untrained eye.
Thanks!
-Fray