Bitrate

Cincyfilmgeek wrote on 9/30/2007, 9:25 AM

I calcaulated my bit rate for my film which is 1 hr. and 4 min and according to it my bit rate should be 8,952,000 which in my understanding you really shouldn't go above 8,000,000. Is this correct? And should I use variable or constant? And in variable what should be the bare minimum?

Thanks.
David

Comments

TGS wrote on 9/30/2007, 2:43 PM

The 8,000,000 limit is something I've only adhered to because of others suggesting it. But it may just be a problem with some older players. If you want to limit yourself to 8,000,000, then make it constant and a single pass is probably good.
As far as your bare minimum of VBR question, that's very subjective and depends on what you mean by bare minimum. Assuming you're a 'filmgeek', I think you mean the absolute best quality without loss of detail. Only your own eyes will give you that answer. My favorite 'general excellent quality' setting is, 8,000,000High, 7,000,000Avg, 4,000,000Low with 2 pass. This will give about 85 Minutes for a DVD 4.7disc 2 pass is great if you have lots of dark areas in your video and need to go below a Constant bit of 8,000,000 due to the length of the video

John_Cline wrote on 9/30/2007, 4:11 PM

The spec for DVD is that the total combined bit rate of both the audio and video streams should not exceed 9.8 mbps at any time.

Some MPEG2 encoders will "spike" occasionally exceeding the maximum which you have set, thus the unofficial 8 mbps limit for the video stream. If you are using a very high bit rate to begin with, this can be a problem. In theory, you could encode your 64 minute video at 9.6 mbps and use .AC3 audio at 192kbps and keep in just under the limit, but this is just asking for compatibility issues with both older players and some "inexpensive" (i.e. cheap) players.

If you use uncompressed 48k 16bit stereo PCM audio, which has a bit rate of 1.536 kbps, you could only use a max video bitrate of 8.2 mbps. You'd still be getting precariously close to the 9.8 mbps limit.

For your 1 hour 4 minute video, you could probably get away with 8.5 mbps CBR and use 192kbps or 256kbps .AC3 audio and keep a safe amount of wiggle room for video bit rate spikes.

John

fwtep wrote on 9/30/2007, 8:41 PM

I agree. It's safest not to set the video rate above 8mbps. And at that rate it should look great. I usually have mine at Constant Bit Rate, and with the length of your video you might be able to do that too.

By the way Cincy, I sent you an e-mail, did you get it?

Fred