What bitrate for 1/2 D1 captures?

[Richard_G]

I'm capturing terrestrial Digital TV using an external receiver into an ATI AIW Radeon 7500 card to archive to DVD-R instead of keeping them on video tape. I want to be able to fit around 2 hours on each DVD-R disk. I normally capture at 720 x 576 (25fps, PAL) using a constant bitrate of 6000kbs, but I then have to drop the bitrate to around 4500kbs to fit 2 hours onto a disk. This is OK for most things but if the content has lots of fast movement I get noticeable mpeg artifacts (blocking, blurred movement, etc). This doesn't appear on the original captures at 6000kbs.

In the past (when I had a slower system) I've tried capturing at 1/2 D1 (352 x 576) and any loss in quality was barely noticeable. Logic would say that if I capture at 352 x 576, I have half the amount of data so I can use a bitrate of 3000kbs and the artifacts would be the same as my full frame captures. I could even up the bitrate to 4000kbs and still be able to fit 2 hours on a DVD-R but the quality should (in theory at least) be better.

Anyone use this resolution? If so, what bitrate is going to give me best quality?

[spectroelectro]

I've done short experiments in NTSC with half D1 as you describe. However, from the couple of test DVD-Rs I burnt I ascertained that the better solution was to encode to MPEG-2 using VBR instead of CBR. Cutting the average bitrate of a VBR-encoded MPEG-2 files encoded with TMPGEnc seems to have surprisingly little effect -- I can see no visible difference moving the average bitrate from 4500 to 6000 provided that he max bitrate is set high enough, viz., 8000 or 9000. Of course VBR makes the length of video you can store on a DVD-R program-dependent, so you might not want to use this solution.
I have found a slight but barely noticeable degradation in video detail by going from full D1 to half D1 (in NTSC that means going from 720 x 480 to 352 x 480). Practically speaking I have found it to be of negligible importance in watching the resultant DVDs.
(So why do I keep burning DVDs with 720 x 480 resolution? Solely to preserve maximum standalone DVD playback compatibility, as my current DVD player shan't last forever.)
If encoding time is the issue preventing you from going to VBR as opposed to CBR, think about either investing in a faster computer (P4 2.4 Ghz bare bones boxes can be had for under $300 in the states) or investing in the inexpensive MainConcept MPEG-2 software encoder. The MainConcept software encoder runs almost 4 times as fast as TMPGenc and produces encoded MPEG-2 VBRs of nearly identical size (only slightly larger) and with nearly as good quality (not quite as good, but close).

[i_am_dave]

I agree with spectroelectric. There is no reason to go to 1/2 D1. You can easily encode 2 hours of video at DVD quality using TMPGenc. Just select 2-pass VBR. There are bitrate calculators in the tools section of this forum that will calculate your average bitrate for you. I would use this, shoose around 2000 for the minimum and 8000 for the maximum.

[Richard_G]

Thanks for the replies. I've kept away from vbr because the resultant file size is content dependant. A particular setting may be fine for one thing but not for another. I've used two different methods of achieving the result. As I said, I'll capture at 6000kbs cbr and then import the file into Ulead DVD Workshop. I can then either adjust the bitrate until I end up with a 4.3Gb file and let it get on with it (encoding speed isn't particularly important as I usually set it up and go to bed or set it up and go to work). An alternative I've tried is to let DVD Workshop do the multiplexing and create and save the vob files to hard drive at the same 6000kbs cbr as the capture. This takes hardly any time at all. I then end up with vob files that are around 5.5Gb (for 2 hours worth of video) which I import into DVDShrink and re-encode to get them down to 4.3Gb and burn to DVD-R.

I can't see any difference in quality between the two methods, the latter is quicker but needs me to be there. Letting DVD Workshop do the job means I can set it up and when I come back to it later, I've got a finished DVD.

I know DVD Workshop will allow me to select vbr but I'm not sure how much control it will let me have (I can set a max rate but not sure if I can set an average). If I was to start using different tools for different bits of the process, I would have to be there. When I'm there I have numerous other things I need to do on the pc (editting my own video, keeping my wifes business accounts, running my own business and keeping my accounts, letters, emails, reading the forums on dvdrhelp.com, and all the other stuff that a pc gets used for these days).

I too have noticed virtually no difference in quality between full D1 and 1/2 D1 in playback. What difference that is there is nothing like as noticeable as mpeg artifacts (on particularly bad bits, even my wife notices them!). Hence the question in the first place. Playback compatibility is likely to be less of an issue as each newer generation of players seem able to cope with more and more formats. I'm likely to change the one I have soon anyway. My current player will play VCD, SVCD, XSVCD and DVD-R but won't touch DVD-RW. It's a good job blank disks are so cheap!

[Jukka]

VBR shouldn't give you variable length files if your encoder has an average bitrate.

In TMPGEnc + use 2-pass VBR, set the average to the bitrate that would fit 2 hours on a DVD, then set the min and max as necessary (but not too radically). Whilst the spikes will have low / high bitrates the average will still be such that it fits on 1 disc (because you used a bitrate calc for 2 hours). CBR is just a special VBR but with min = max = ave.

Hope this helps,

Jukka

[lordsmurf]

If your source is only VHS or television, anything over 352x480 is really unnecessary.

The max bitrate for 352x480 is 4.0 MB/s or 4000k. It's the same as 8000k or 8.0 MB/s at 720x480.

I'd take a 352x480 4.0 MB/s CBR or VBR encode any day over a 720x480 6.0 or 5.0 encode, no matter if it's CBR or VBR. Anything under 7.0 is just too darned low, and will normally resulting in loss of dark areas and macroblocking.

That said, however, some cards and encoders simply perform poorly at 352x480 Half D1, so I can see where this argument comes from.

[Richard_G]

I'd take a 352x480 4.0 MB/s CBR or VBR encode any day over a 720x480 6.0 or 5.0 encode, no matter if it's CBR or VBR. Anything under 7.0 is just too darned low, and will normally resulting in loss of dark areas and macroblocking.

Thanks Lordsmurf, that's exactly the information I was looking for. 1/2 D1 at 4Mbs should give me over 2 hours on a DVD-R and has got to be better than full D1 at 4.5Mbs. The logic said it should be equivant quality to full D1 at 8Mbs, I just didn't know if it was that simple.

The source is digital TV captured via S-video so is better quality than normal analogue TV and far better than VHS. That's why I'm capturing and saving to DVD-R, I want to retain the quality and not drop it down to VHS standard.

Thanks everyone, I'll give it a try next time there is something I want to capture.

[Metaluna]

If your source is only VHS or television, anything over 352x480 is really unnecessary.

The max bitrate for 352x480 is 4.0 MB/s or 4000k. It's the same as 8000k or 8.0 MB/s at 720x480.

I've been encoding VHS captures at 352x480 and 5000k bitrate in TMPGEnc for a while now (just because I always have plenty of room on the disc so I figured why not). Are you saying that these are non-compliant MPEG2 streams? I've not had any problems with compatibility so far but I don't have access to that many players to try out.

[lordsmurf]

Are you saying that these are non-compliant MPEG2 streams?

No, just wasted bitrate.

[ronnylov]

EDIT: Sorry I posted a question that already was answered.
Deleted.

[MrKGB]

I always use 1/2 DVD for cable captures.
I use CCE for encoding, in single pass VBR mode, and I can fit about 5 hrs of video on DVD with very good quality.
I like single pass VBR mode because it is very fast and gives predictable quality, but not predictable size, which is exactly what i want.
I don't really care about size considering that I can fit 5 hrs on DVD