Crop without Re-Encoding - version 0.0.9x r2 - Several questions?

[llee782]

Actual video content is 2.35:1. Captured content is 4:3 (black bars at top and bottom). File is 29.97 fps mpeg program stream (.mpg). I want to crop to anamorphic proportions to burn as a 16X9 DVD. I don't want to re-encode, just to crop. Here are my steps.

1. Drag .mpg file to ffmpegX window with summary segment tab selected.
2. Select DVD ffmpeg preset.
3. Select Passthrough in Video segment tab.
4. Select Autosize: DVD 16:9 in Video segment tab.
5. Set Video Bitrate to match that of original file in Video segment tab.
6. Select Passthrough in Audio segment tab.
7. Add "60" to 1st and 2nd Autocrop fields in Filters segment tab.
8. Select Deinterlace in Filters segment tab.
9. Deselect "Author as..." checkbox in Options segment tab. (I will author using a method that adds chapter menus)

An .avi file results. This file can be played successfully using VLC with the proper aspect ratio.

Even though Passthrough is selected, video bitrate is severely deprecated (more than would seem to be a result
of the cropping) if I don't include step 5. Why?

The file won't play in QuickTime Player with mpeg 2 playback component installed unless I rename it with the .mpg
name extension. Why?

Whether or not I rename the file with the .mpg name extension, it won't be recognized as a video file by Toast (8.0.1) unless
I edit the beginning of the file with a hex editor (I used Hex Fiend) so that the first 44 bytes of the file consist of the hex values

00 00 01 BA

followed by zeros.

Why is editing the first 44 bytes of the file in this manner necessary to make it compatible with Toast?

Thanks.

[ingemar]

If you want your end result on dvd as anamorphic, the source needs to be 5:4, 720x576. If you would calculate anamorphic from 576 height you'd end up with 1024 wide which does not comply to the dvd standard. Anamorphic dvd's are nice, but a little bit fake because the player stretches the 720 image to 1024 for playback, or letter boxes it on 5:4 displays. Check this article.

I tried to figure this out but I don't think its possible to truly passthough, I think the best you can do is select the same bitrate and hope for the best.

But what I really don't get is if you want the end result to be DVD, is why you first go to AVI mpeg4? That extra step will degrade quality, no matter how high a bitrate you choose. I would go from mpeg to mpeg, crop it and scale it to 720x576, ready to be moved to dvd, which I think ffmpegx can do for you under tools. One step, with the least loss in quality.

[llee782]

But what I really don't get is if you want the end result to be DVD, is why you first go to AVI mpeg4? That extra step will degrade quality, no matter how high a bitrate you choose. I would go from mpeg to mpeg, crop it and scale it to 720x576, ready to be moved to dvd, which I think ffmpegx can do for you under tools. One step, with the least loss in quality.

When you choose Passthrough in the Video segment tab, format automatically gets switched to avi in the summary segment tab. The more clips I try, the more I believe that there really doesn't seem to be a way to insure that bitrate stays up when using the Passthrough option. So my question now is how do you crop losslessly? Thanks.

[tomlee59]

I am sure that "passthrough" is not really passing through. The fact that your video bitrate changes sort of reveals that. So, first abandon the notion that you can get by without reencoding.

Just go directly to the final target format, as the previous poster wisely suggested. I am not aware of any way to crop losslessly, given the way mpeg works, unfortunately. I'd love to learn otherwise, but I just don't see how. The standard does not allow for a simple XOR mask to overlay on top of your video to produce the effect of a crop. Given how the value of every encoded pixel depends on groups of other pixels, the cropping of any pixels will have a global ripple effect. This means that you can't just "passthrough" and crop simultaneously.

[llee782]

OK, so I'm trying this:

/Users/me/Applications/ffmpegX_0.0.9x/ffmpegX.app//Contents/Resources/ffmpeg -i '/Users/me/Desktop/clip.mpg' -y -threads 2 -map 0.0:0.0 -deinterlace -target ntsc-dvd -b 7600 -aspect 16:9 -croptop 60 -cropbottom 60 -cropleft 0 -cropright 0 -s 852X480 -r ntsc -g 12 -me epzs -qmin 1 -qmax 11 -intra -acodec copy -map 0.1:0.1 /Users/me/Desktop/cropped_clip.ff.mpg

[Case]

-s 852X480

852x480 is not a valid size for DVD Video.

If you re-size, you have to re-encode. Cropping 2x 60 from 720x480 results in 720x360. To scale that back to 720x480 thus requires encoding the video again.

[llee782]

852x480 is not a valid size for DVD Video.

I know, I saw those numbers (numbers close to that, but not exact, actually) from here and it was a mistake to use them in my example. I tried several methods to optimize quality, and I that's one I tried, which of course required re-encoding again, which wasn't recommended.

If you re-size, you have to re-encode. Cropping 2x 60 from 720x480 results in 720x360. To scale that back to 720x480 thus requires encoding the video again.

So does resizing to a valid size from 852X480, as noted. I'm not cropping from 720X480, my source is 640X480. I'm trying to crop enough of the black bars at top and bottom so that when I switch from 4:3 to 16:9 dimensions, the aspect ratio of the content will remain intact.