DVD vs PVR Picture Quality

[Bogey62]

Could someone explain to me, in semi-laymen terms, the difference between DVDs and the 721 PVR's picture quality? Is it just a matter of bandwidth or maybe a difference in compression schemes? The picture quality on HBO is horrid as compared to my C-band analog signal and a DVD played back on the TV.

Thank you. :)

[scooper]

It's a matter of compression from Dish. HBO is getting more bandwidth than most channels, but it still isn't much more than 3 Mbps. Your DVD is probably generating 5+ Mbps.

[zimm0who0net]

Does anyone know the true bitrate of a DVD? My rough, back-of-the-envelope calculation indicates that if a DVD holds roughly 3 hours of video on 5GB of storage you end up with around 3.8Mbps for an average bitrate.
That's certainly higher than the bitrate E* is sending us, but not as dramatically higher as I would have expected.

[drjake]

DVD's with more than 2 hours of video are typically dual layer. Therefore, the capacity is 9.4 gigs (8.8 gigs in real computer terms). Typical DVD bit rates go from 5.5 Mbps to 8 Mbps.

[Mike123abc]

DVD max bit rate is around 10mbit/sec. Now you have to subtract from that rate all sorts of stuff like subtitles, multiple soundtracks, etc. A sound track could be for example 384kbit/sec. Two soundtracks and a few subtitles could use up 1.5 mbit/sec leaving less than 8.5 mbit/sec peak video rate.

A DVD may have a video feed average of 3.5 Mbit/sec (what I last saw as average for most movies). But could have a peak rate of 8mbit/sec during certain scenes. DVDs also have some advantages over Dish:

1. Compression on DVDs takes weeks to do. Difficult scenes are worked over by hand (i.e. tuning compression on each frame). Pearl Harbor for example took 6 weeks for the compression to be finished. Compression on DBS has to be done in real time.

2. Many film DVDs are in 24p. This saves 25% overhead over the 30fps video has to do. The mpeg bit stream is flagged that it is 24p and your decoder does the 3:2 pull down to get it to 60 fields/sec (30 frames). DBS does not have this advantage either, plus the signal comes in interlaced so it is harder to compress.

3. DBS has has to share the bit stream with other channels. A DVD could have a 10 minute run at max bit rate for a big action scene where DBS has to share with other channels, it can adjust bit rates somewhat, but hard to maintain high rates for a long time because other channels may need to peak at the same time.

[md_paul]

My Toshiba DVD player has an info button that displays (along with other information) the current image bit rate. I've noticed that most large budget DVD movie releases have a variable bit rate depending on the action and motion on the screen that is similar to the postings above (4 - 8+ mbit/sec).
However, many more cheaply produced DVDs (mostly the one's I've purchaced for my kids) seem to play at a constant 10mbit/sec bit rate with no variance througout the entire DVD. These 10mbit/sec bit rate DVDs are usually no clearer than the 4-8mbit/sec discs. As a matter of fact, most of these videos seem inferior with noticeable compression on quite a lot of scenes. I suppose time and effort spent on quality compression like that on the big-budget hollywood DVD's really can make a larger difference in the picture quality than just the bit rate.

[Bogey62]

Wow, thanks for all the info, guys! :)

[Mark Holtz]

Don't forget, there is a lot more going on with the bitrate than just the picture. Some of the more deluxe versions of the DVD can include multiple audio tracks for commentary/foreign language, subtitles, and so on.

How long were the kids videos anyways?