Maximum Bitrate - How Does it Work?

[GParent]

I read the FAQ and did some searches. Still have questions about Max Bitrate.

First, this is what Jim Taylor says in his DVD FAQ:

"Maximum video bit rate is 9.8 Mbps. The "average" video bit rate is around 4 Mbps but depends entirely on the length, quality, amount of audio, etc. This is a 31:1 reduction from uncompressed 124 Mbps video source (or a 25:1 reduction from 100 Mbps film source). Raw channel data is read off the disc at a constant 26.16 Mbps. After 8/16 demodulation it's down to 13.08 Mbps. After error correction the user data stream goes into the track buffer at a constant 11.08 Mbps. The track buffer feeds system stream data out at a variable rate of up to 10.08 Mbps. After system overhead, the maximum rate of combined elementary streams (audio + video + subpicture) is 10.08. MPEG-1 video rate is limited to 1.856 Mbps with a typical rate of 1.15 Mbps."
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I'm creating DVDs with LPCM audio which generates a 1.5 Mbps stream. If my video max is 9.8 Mbps, and I have no subpicture, the total that could potentially be reached is 11.3 Mbps, which exceeds the formula.

What will setting DVD Compliant do for me if CCE is not aware of my audio stream. It seems it would need prior knowledge of my audio bitrate and subpicture bitrate, to guarantee the video encoded stream does not exceed the true maximum. Also, what is the true maximum. Jim Taylor is just giving the official DVD specs because he probably helped write them, but the average DVD player may be under spec'd or over spec'd.

If I'm using LPCM and no subpicture, should I just set a max bitrate to 8.0 Mbps, and that would guarantee the total would be under 9.8 Mbps, in a safe zone. Also, would it also be best to uncheck DVD Complant in CCE 2.66, beacuse it would just allow CCE to over ride the 8 Mbps max I set.

There is an unbelieveable amount of wrong headed thinking about this in other newsgroups and forums. I'm sure some of my thoughts are wrong. I'm here to get it straight.

Thanks,

Gary

[Clown shoes]

I may be wrong Gary, but I believe that the DVD compliant setting is just a ceiling, preventing the bit rate from exceeding 9,800. I have produced quite a few comercial DVDs and never had a problem using this flag. Even when PCM wavs were required. I just set a max bit rate of 8,000 and ran a few passes.

Clown Shoes

[GParent]

Right now,I am playing a DVD where the MPEG has the Max Bitrate set at 8000_Kbps, and the LPCM is fixed at 1536_Kbps = 9536_Kbps < 9800_Kbps.

Although I no longer have it in my possession, I can remember the same project showing an occasional jump to a video bitrate of 9800_Kbps. In that case, I had the max set to 8000_Kbps, but the DVD Compliant flag was on.

When I played that previous project, I would occasionally see the Video bitrate jump to 9800_Kbps. This convinced me to back off and ignore DVD Complant and just set my own maximum.

Note that the project I worked on is only a 60 minute video and there is no problem of fit, therefore the bitrate can be high.

I was just wondering if anyone else has had a similar experience?

In addition, the 9.8_Mbps ceiling is just for video. Therefore, it is within spec to have a very high video stream rate, with the proviso that your audio rate is not LPCM. Why? Do the math. A 1536_Kbps LPCM audio stream would put you over the overall max of 10.8_Mbps. The lesson is to make the audio compressed (eg. AC3), or use LPCM but ensure the maximum never exceeds approximately 9_Mbps, a good ceiling.

Gary

[GParent]

Correction to my last sentence, in the previous message.

The lesson is to make the audio compressed (eg. AC3), or use LPCM but ensure the maximum VIDEO BITRATE never exceeds approximately 9_Mbps, a good ceiling.

[symonjfox]

I don't understand why you want to keep audio in LPCM? You can encode it in MP2 @ 384 kbs if you want, and it sounds like LPCM and you have no problems with bitrates ...

[GParent]

>>I don't understand why you want to keep audio in LPCM? You can encode it in MP2 @ 384 kbs if you want, and it sounds like LPCM and you have no problems with bitrates ...<<

I made a music DVD for commercial mastering and sale. I didn't have the software to create a licensed Dolby 2.0 audio, so I went with the cheapest way that I felt was a common denominator on every player for the US market (Region 1). I picked LPCM, an uncompressed format that is a no brainer, it works on all DVD players I tried, and I feel it will do the same on others.

Regards MP2, I don't feel comfortable going with that format, and the risk of having potential problems.

[r6d2]

If I were you, I'd abide by the specs. Set the Max to: Max_by_Specs - Audio_bitrate - Muxing_Overhead.

Set the AVG to whatever value to need to fill the disk. As Clown Shoes said, the max is an upper limit not no be trespassed by the encoder, even though it may actually do it at certain frames.

Any MPEG-2 encoder has the duty of adjusting the output video stream VBV in order to play your encode on any compliant device.

[symonjfox]

Originally posted by GParent
[BI made a music DVD for commercial mastering and sale. I didn't have the software to create a licensed Dolby 2.0 audio, so I went with the cheapest way that I felt was a common denominator on every player for the US market (Region 1). I picked LPCM, an uncompressed format that is a no brainer, it works on all DVD players I tried, and I feel it will do the same on others.[/B]

Maybe you're right. I read somewhere in the forum that NTSC DVD Players may have trouble if there's only an MP2 Audio Track. I don't know other particulars, because I live in PAL world and it works great in my Standalone DVD Player.

[GParent]

In CCE, I set the following:

(1) MAX = 8000
(2) AVG = 7000
(3) MIN = 1500

When I run INFO STATUS on Power DVD 5.0, it shows that the bitrate realtime readout stays in the high 6500-7900 and never goes over 8000.

When I created the DVD using DVD Lab, the built-in bitrate viewer, verified the MAX = 8000 and AVG = 7000.


UNFORTUNATELY THERE IS A PROBLEM WITH TECO Bitrate Viewer:

Perhaps I am not using the following popular utility properly. When I run the same MPEG through TECO's Bitrate Viewer, version 1.5.054, I get different results that are not accurate:

PEAK = 6855
AVG = 5363


Num. of picture read: 31
Stream type: MPEG-2 MP@ML VBR
Resolution: 720*480
Aspect ratio: 4:3 Generic
Framerate: 29.97
Nom. bitrate: 8000000 Bit/Sec
VBV buffer size: 112
Constrained param. flag: No
Chroma format: 4:2:0
DCT precision: 10
Pic. structure: Frame
Field topfirst: Yes
DCT type: Field
Quantscale: Nonlinear
Scan type: Alternate
Frame type: Interlaced
Scene change detection: NOT FOUND
Variable GOP pattern: NOT FOUND
Notes: