New to Video Bitrates

reberclark wrote on 5/22/2008, 9:04 AM
My video imported from my camera comes in as an Mpeg-2 at a bitrate of 9.6mbps. I know nothing about how bitrate affects the final render. I can change this rate in DVD Patcher but have no idea which rate (if any) is more advantageous. On the boards I have seen 8mbps as the top rate and 6mpbs recommended as a "safe" rate. I have no idea what these rates accomplish. Please advise me. I render my video to NTSC DV Widescreen for DVDA and the Audio to AC-3 or WAV. Thanks.

Comments

Mikey QACTV7 wrote on 5/22/2008, 11:01 AM
Real basic: The higher the bitrate the better the quality of video. WARNING most DVD players will not playback higher than 8bps. So 6 bps is a safe level for playback. And the higher the bitrate the larger the file. If you use mpeg-2 video on your Vegas timeline check to see if it is upper-field or Lower-field first. If you render out another mpeg-2 you will have to set your render properties to match the video. If you are seeing a weird motion trail on your TV during playback then you need to reset the field for your render. To check the field order 1) place your mpeg 2 file in vegas. 2) right click on your file and select properties 3) you will see the field order toward the bottom.
kentwolf wrote on 5/22/2008, 12:23 PM
>>...6 bps is a safe level for playback...

Ditto.

I do everything at 6.

Higher than that, you run the risk of the DVD player choking. I even had one choke at 7.

At 6, I have never had a DYD fail to play anywhere. It still looks good too. It doesn't matter how good the video looks if the DVD player locks up.
reberclark wrote on 5/22/2008, 9:46 PM
Thanks guys. Excellent advice and well worth it.
johnmeyer wrote on 5/23/2008, 7:56 AM
How do you know the bitrate of the video from your camcorder? Many DVD patching software program report that bitrate incorrectly. The very latest GSpot finally does it correctly, by reading all the way through the file rather than reading some header. It takes a few minutes before you get your answer.

I doubt that the video from your camcorder is 9.6Mbps.

However, I must disagree about keeping your final renders as low as 6.0 Mbps. I've read hundreds and hundreds of posts similar to these, and so far believe that the problems people get are due to using bad media. The reason is that ALL DVD players are required to play at more than 10 Mbps. The following quote from this document

mpeg.org Video Data Specifications

provides the official story (sorry about the CAPS, but that is how it appears in the document):

"ALL DVD PLAYERS MUST SUSTAIN A 9.8 MBIT/SEC VIDEO DECODE RATE!!!!!!! "
At 6 Mbps, you will definitely begin to see significant encoding artifacts that were not present in the original material. From my experience, this is the "magic" point at which MPEG-2 encoding, as implemented for NTSC DVD, begins to break down. I generally encode at 7.0 - 7.5 Mbps (that would be 7,500,000 in the Average setting under the Custom button in the Render As dialog). I leave the min and max bitrates at the default settings.

I usually duplicate between 30 and 70 copies of each of my "productions." I have now had, in the past four years, exactly three returns, and I tracked down each one. Two were players that were dying, and one was a player that didn't like DVD-R (which is usually the most compatible). I keep a few DVD+R discs around, figuring something like this might eventually happen. I burned that disc (which was encoded at 7.0 Mbps, if I remember correctly) and it worked fine.

So, I can still say that I haven't had a return due to bad media or improper encoding.

riredale wrote on 5/23/2008, 8:18 AM
Agreed. I sometimes encode at 8 (not including the audio) and never have issues.

At the other end, with careful use of an excellent multi-pass MPEG2 encoder such as CinemaCraft, I can easily bust the 6 barrier without any artifacts. A "4" average for video is about as low as I ever go, which works out to be about 2:20 on single-layer.
johnmeyer wrote on 5/23/2008, 8:33 AM
At the other end, with careful use of an excellent multi-pass MPEG2 encoder such as CinemaCraft, I can easily bust the 6 barrier without any artifacts. A "4" average for video is about as low as I ever go, which works out to be about 2:20 on single-layer.

I'll agree right back at 'ya. With two-pass and -- if you really want to get into it -- an external encoder with custom encoding matrices, and all sorts of tricked out settings -- it is possible to get pretty good results are very low bitrates.

Years ago, before my first DVD burner, I started encoding VCD (yuch!), then SVCD, and later XVCD, which were done at absurdly low bitrates. The VCDs all look terrible because 320x240 MPEG-1 progressive has no chance of looking good. However, I am amazed at how good those SVCD and XVCD discs look.

I've done some DVD encoding way down close to 2.0 Mbps average. With off-the-air material, (not movies but sitcoms, etc.) it can look pretty darned good. I've done the Masters golf tournament the past three years. The final day is over four hours long (although this year I did finally put that on a dual layer).

However, at these ultra-low bitrates, if the program material contains a dissolve or use smoke, or has a nice shot outside with a big clear blue sky, it ain't gonna be pretty for a few seconds ...
reberclark wrote on 5/23/2008, 10:45 AM
Thanks for the follow ups. I really can't say I "know" that my mpegs are coming in at 9.6mbps. You are right that DVD Patcher is just reading and giving me header info (that is where I am getting it). This has given me much more to research. Thank you for the additional info!
johnmeyer wrote on 5/23/2008, 11:22 AM
Here's where you can get GSpot. Just download and run (no installation required):

GSpot

Drop your video on the GSpot window, and then on the right side, watch the "kbps" readout. For a big MPEG file, it will take 30-60 seconds (or longer) to reach a final answer, because it has to scan the entire file. However, in a few seconds you will see a number that will be pretty close the final number.

[Edit]

P.S. If you use single pass VBR encoding in Vegas, the actual average bitrate that Vegas puts out actually doesn't come very close to what you set. Call it a bug, or just sloppy programming. However, if you use 2-pass, the resulting average bitrate will be within a few digits of exactly what you set. This is not to say that you should use 2-pass all the time: generally I don't use it unless the bitrate is below 6,000,000.



bStro wrote on 5/23/2008, 12:12 PM
I can change this rate in DVD Patcher but have no idea which rate (if any) is more advantageous.

For the record, since I don't think this was mentioned in the thread, you can't really change the bitrate using DVD Patcher. The bitrate is the (approximate) number of bits that the encoder will dedicate to each second of video. The only way to change the bitrate would be to re-encode the video.

DVD Patcher just changes the information in the header of the file. In fact, I believe this goes for everything that DVD Patcher "changes" -- you're not really changing the content, just the header. In effect, DVD Patcher is "lying" in order to make something -- be it another program or a DVD player -- believe that the file is something it's not.

For example, if I try to give DVD Architect a video that has a resolution of 480x480, it will want to re-encode it to a standard resolution like 720x480. But I know that at least one of my DVD players can play a 480x480 video just fine -- if only I can slide it past DVD Architect. So, I use DVD Patcher to change the header so that DVD Architect thinks the file is already 720x480. But after I prepare the DVD files but before I burn them to disc (at which point DVD Architect isn't "looking" anymore), I use DVD Patcher again to give the file the correct header -- otherwise, my player will freak out a bit.

But that's not really going to help for something like bitrate. The issue with a high bitrate is that a DVD player will have trouble keeping up with the data being retrieved from the disc. (It's more of a problem with burned DVDs than pressed DVDs because they're a little harder to read.) And no matter what the file's header says, it's still the actual bitrate that your DVD player will have to deal with.

Rob
johnmeyer wrote on 5/23/2008, 1:14 PM
bStro is exactly correct. Also, I too use DVD Patcher to take my old 480x480 SVCDs and put them on DVD without re-encoding by temporarily patching the header so the file will "lie" to DVDA and make it "happy" with the non-standard file. The only issue is that the target DVD player still has to be capable of playing SVCDs, which not every player can do.

Actually, someone told me -- can't remember if it was an email or in this forum -- that the newest DVD players no longer play SVCD. Don't know if that is generally true or not ...
Chienworks wrote on 5/23/2008, 1:55 PM
There's probably a good deal of truth to that. All three of my old DVD players died recently (on Christmas eve of all times, what are the odds?). I replaced them with some new Magnavox models. The old players would take just about any disc i stuffed in them and play almost any media that was on them, regardless of format or type. The new ones will play only standard video DVDs and audio CDs. They ignore everything else.
hazzardm wrote on 5/27/2008, 4:55 AM
Thanks so much for this insight!
My mothers DVD player would not play anything I produced for her. After setting the bit-rate to constant 6 Mbps, they now play fine!
Widetrack wrote on 5/27/2008, 7:19 AM
Sorry if I'm missing something basic, but doesn't the bitrate of your rendered file depend on how you set it at rendering time? And can't you render any video at any bitrate Vegas supports?

My understanding has been that you could even render using source material that has a lower rate than your final render. The low-rate material won't get any better-looking, but it would play back at whatever bitrate your final render is set to deliver. Is this correct?

I just posted a related question under the assumption that this is true, and I hope I'm not laboring under a false assumption.
kentwolf wrote on 5/27/2008, 1:02 PM
>>...can't you render any video at any bitrate Vegas supports?...

Yes.

>>...but it would play back at whatever bitrate your final render is set to deliver. Is this correct?...

Yes.
kentwolf wrote on 5/27/2008, 1:06 PM
>>...After setting the bit-rate to constant 6 Mbps, they now play fine!...

This has been my experience.

I know that DVD players are *supposed* to sustain a substantially higher bit rate, but I almost wonder if it can be an issue of the laser wearing out, which I have also seen. It is my understanding that this (wearing out) is a gradual process.

I know that 6 Mbps was the (CBR) default value in the Main Concept stand-alone MPG2 encoder.
bStro wrote on 5/27/2008, 1:49 PM
Sorry if I'm missing something basic, but doesn't the bitrate of your rendered file depend on how you set it at rendering time? And can't you render any video at any bitrate Vegas supports?

Correct.

But the original poster in this thread isn't rendering out of Vegas. He's taking footage from his camera (which is already MPEG2) and putting it directly into DVD Architect. And to avoid having to re-encode it to lower the bitrate, he was hoping to use a third-party tool called DVD Patcher.

Rob