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can I crop a m2v file without loss?

cleantone posted 2008 Aug 27 20:11

I have been scratching my head for days trying to get something done. In short the project I am in the middle of is... I have a source DVD (video_ts) that is letterboxed. I have two goals. One was to demux and remaster the audio. I have done that. I plan to and know how to reauthor a DVD that has two audio tracks. The remastered on one and the origional on another. So far I am good to go. Ideally I would like to crop this film without recompression before reauthoring. I have the m2v file in full resolution. It could use some cropping on all four sides to loose some black bars and look more like it's origional 2.35:1 ratio. So is this possible without reencoding the m2v file? If so what is a good way to do it?

gadgetguy posted 2008 Aug 27 20:20

No. Since your goal is to author back to DVD, the resolution has to be 720x480. If you crop, you'll have to resize back to spec. You can't do that without reencoding and as you know, you can't reencode without loss.

cleantone posted 2008 Aug 27 20:26

How about a resizing or upscaling that will have minimal effect on quality?

manono posted 2008 Aug 27 20:39

You seem to have a widescreen 4:3 DVD (letterboxed) and want to crop and resize it to be able to encode it as 16:9. Whether true or not, any cropping and/or resizing requires a full reencode. How well you do the job and how much the resulting video is degraded depends at least partly on how much you know and what tools you use for the job.

gadgetguy posted 2008 Aug 27 20:45

I don't use MAC, so I don't know what tools are available there, but I prefer Lanczos for resizing. To my eyes, it gives the best results. Of course, regardless of what you use to resize there will be some loss, but only you can judge if the loss is acceptable.

Herve posted 2008 Aug 28 07:24

like said before... cleantone : I would like to crop this film without recompression before reauthoring. not possible, mpeg2 is made of "a jpeg frame and its transformation to the next jpeg frame" (so if you change something in the jpeg frame -like geometry- the remainder will be non concordant) so you must re-encode PS: 2.35:1 is a valid dvd aspect (like 1:1) but there are just a few dvdplayer able to read it (so crop a 4:3letterbox to 16:9, but not to 2.35 ;)) cleantone : How about a resizing or upscaling that will have minimal effect on quality? depending on the contents of your file. If your video is basic (not interlaced) almost every soft can produce a not bad result. If your source is interlaced: only mpegstremclip, jesdeinterlacer, avisynth and mine(see sign) can do the job bye

cleantone posted 2008 Aug 28 08:00

hmm. I don't know if it is interlaced or not. Can you find out from the source material alone? If so how?

Herve posted 2008 Aug 28 08:31

open your file in VLC, do not activate "deinterlacing filters". Do you see comb's effects during playback? if no, the contents of your file is progressive (not interlaced) bye

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