2-Pass VBR range limit for H.264 encoding?

[Winsordawson]

Does anyone know if the range of a 2-pass VBR has a limit? For example, I read on this site that the target and max bitrate for a NTSC VHS in h.264 is 5.5 and 8 Mbps, respectively. If I set the target bitrate as 3.5 Mbps, but leave the maximum bitrate at 8 mbps, will the NLE know where to allocate bits and produce the same quality as a 2-pass VBR that has a target/maximum of 5.5/8? I don't care if it would take longer to render. Thank you.

http://www.digitalfaq.com/forum/vide...4-produce.html

[lordsmurf]

This question doesn't make sense.

MPEG has max bitrate for the DVD-Video spec, but that's really about it.
Blu-ray (BDMV/BDAV) has limits as well.

H.264 has no such limit, and what you've written is very arbitrary. Perhaps certain devices have limits, but I've never encountered anything that chokes on anything below 15mbps (SD res). H.264, especially x264, has different methods on VBR, more than MPEG did.

Encode time mostly depends on bitrate, and encode options with H.264/x264.

[Winsordawson]

I am trying to save space by reducing the bitrate to a non-noticeable extent. If I have footage with a bitrate of 18Mbps, and want to convert it to h.264 to save space, usually I would output small parts at various bitrates to see if the quality changes much. But I wondered if I could just use 2-pass VBR and leave the target bitrate low but keep the max bitrate high to allow for scenes that require more bits, such as those with a lot of movement. I noticed that when I do this, the video quality stays pretty poor, even with a high max bitrate.

[lordsmurf]

You need to learn to use Hybrid. Size is not just about the bitrate, but the other settings. I want to make a guide for this, but am waiting until the site facelift is done. Even for the bitrate, you should use CRF mode instead, not VBR outright (2-pass or not).

It's also about resolution, bits to pixels, and 720p with a good bitrate is better than a starved 1080p.

I need to see a sample of what you're working with as source to shrink.

[Winsordawson]

Thanks. What do you mean by "hybrid" in terms of Premiere Pro? Is there no benefit to 2-pass VBR?

I have different videos, so bitrate will vary. But I have read that the main factor is the amount of motion. So I usually encode with a High profile and use the following calculation, with 1 = low motion, 2 = medium motion, and 4 = high motion:

1280 × 720 @24fps, medium motion (rank 2):
1280 × 720 × 24 × 2 × 0.07 = 3,096,576 bps = ~ 3000 kbps
If the motion is high (rank 4), it’s about 6000 kbps.

"In other words, to estimate the optimal H.264 bit rate value that would give what is considered “good quality” results for a given video, you could multiply the target pixel count by the frame rate; then multiply the result by a factor of 1, 2 or 4, depending on its motion rank; and then multiply that result by 0.07 to get the bit rate in bps (divide that by 1,000 to get a kbps estimate or by 1,000,000 to get a Mbps estimate)."

I have attached the document where I got this from.

[lordsmurf]

Hybrid: http://www.selur.de

[Winsordawson]

Thanks, so I would export from Premiere as Pro Res or DNX and then use Hybrid to convert to h.264? Either way, I would still be unsure of what bitrate to use. How does it compare to Adapter?

https://macroplant.com/adapter