Dual layer DVD movie quality?
November 17, 2009 3:32 AM   Subscribe

Question about burning movies onto dual-layer DVDs...is the quality better?

I have ripped both Blu-ray as well as standard DVD quality movies on my hard drive and wonder if I should get dual-layer DVDs for watching them on my (normal, analog, non-hi-def) TV. I've burned many a CD and DVD but don't really know anything about dual-layer. Is the quality better than a normal DVD burn? Which frankly can be pretty sketchy in quality.

I'm using an Intel iMac, btw
posted by zardoz to Computers & Internet (7 answers total) 2 users marked this as a favorite
A dual-layer disc stores twice as much as a single-layer disc. With a dual-layer disc, therefore, you can either choose to store more video, or store the same video with less or no compression (compared with the original video source), i.e. the quality will be the same or near the original DVD.
posted by Blazecock Pileon at 3:53 AM on November 17, 2009

A normal commercial DVD will usually be dual-layer, and will therefore need recoding with higher compression to fit on a single layer DVD-R. If you're going to burn to dual layer, there's enough room to make a block-for-block identical copy of the source DVD, and this should be indistinguishable from the original when played.

I have no experience with Blu-ray media, but if these are also available in both single and dual layer variants then the same would probably apply to those.
posted by flabdablet at 3:57 AM on November 17, 2009

The only difference is available storage space. A single layer gives you ~4.7Gb of space to store the files, whereas a dual layer gives you ~9.

So if you're ripping a single layer DVD, you'll see no quality change when burning to a single layer DVD. If you're ripping a dual layer DVD, you'll a quality change for the worse when burning to a single layer DVD. If you're ripping a dual layer to a dual layer, you'll see no change.

I personally rip only the main track from DVD's, and there are very few dual layer DVD's out there that warrant ripping the entire disc. Lots of manufacturers just fill the extra space with fluff nobody watches so they can list extra "features" on the disc sleeve.

If you were ripping blu-ray and transcoding to dvd (eww) I'd think you'd definitely want to go dual-layer DVD, because your file containers are soooooooooooooo many orders of magnitude larger for blu-ray.

And, for the record, I don't think that a DVD disc can throw true HD in the DVD file format. (Meaning you could burn a 1080 .mkv rip of a movie TO the dvd and watch it in your computer, but it won't play in your DVD player as such.)
posted by TomMelee at 3:58 AM on November 17, 2009

Also, depending on your ripping method, what ends up on your hard disk might not be as good as what was on the DVD you ripped. Generally if you're using some process whose input is a commercial DVD and whose output is an AVI or MOV file containing the main feature, you'll be causing transcoding and additional compression during the ripping process.

For my own DVD backups, I use Gnu ddrescue with lsdvd and libdvdcss2 to make block-for-block copies. These burn space but the quality is the same as that of the originals.
posted by flabdablet at 4:04 AM on November 17, 2009

DVD's are MPEG2, which don't compress very well. If you are transcoding to MPEG4 using a modern codec (xvid, x264, ffmpeg4, etc) with the appropriate settings and a high enough bitrate, it will be significantly smaller in size with no noticeable degradation in quality. They can fit on a SL-DVD with ease and room to spare. BluRay is another matter. You will lose quality simply because there is not enough room to keep the same quality while shrinking the size in half.
posted by cj_ at 4:12 AM on November 17, 2009

(Also: If you are transcoding a 1080p BluRay to fit on a SL-DVD, you really need to rescale it or it will have visible artifacts at the level of compression you will need to use in order for it to fit. Keep in mind a decent x264 transcode of a 720p source is ~6-7 gigs. A SL-DVD can only hold 4.3)
posted by cj_ at 4:23 AM on November 17, 2009

For your non-HD set, I wouldn't bother with dual layer discs, and depending on your connection type (composite/svideo/component), you might not even see any visual difference. Also, dual-layer discs cost about 5x more than single layer discs.

If you ever upgrade your set, you should be reencoding your Blu-ray rips to AVCHD.
posted by wongcorgi at 4:50 PM on November 17, 2009

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