Target Bit Rates for HD

[Bman.]

You guys have been a lot of help the past couple of nights. Thanks a lot. A few more questions -


1) Is there a target bitrate I should encode at to maintain an HD video?

2) Ultimately what function of quality does the bitrate impact? Is it truly a function of sharpness / pixilation?

From Wiki:

Video

* 16 kbit/s – videophone quality (minimum necessary for a consumer-acceptable "talking head" picture using various video compression schemes)
* 128 – 384 kbit/s – business-oriented videoconferencing quality using video compression
* 1.25 Mbit/s – VCD quality (with bit-rate reduction from MPEG-1 video compression)[citation needed]
* 1374 kbit/s – VCD (Video CD) – audio and video streams multiplexed in an MPEG-PS
* 5 Mbit/s typ – DVD quality (with bit-rate reduction from MPEG-2 compression)
* 8 to 15 Mbit/s typ – HDTV quality (with bit-rate reduction from MPEG-4 AVC compression)
* 29.4 Mbit/s max – HD DVD
* 40 Mbit/s max – Blu-ray Disc


3) Where does WMV encoding rank in the scale of compression in say comparison to DivX? I made an HD video last night - 10 minutes long and landed around 300mb. (encoded at 6 mbit / 29 fps)

Thanks again-

Benjamin

[mh2360]

3) Where does WMV encoding rank in the scale of compression in say comparison to DivX? I made an HD video last night - 10 minutes long and landed around 300mb. (encoded at 6 mbit / 29 fps)

It depends on which flavour of WMV you use, generally the older the codec, the worse the compression.

WMV7 is pretty useless for anything but internet streaming.

WMV8 is no good for HD, but can be used for excellent DVD conversions, but you do need to give it almost as much bitrate as MPEG2 and put every advanced quality setting on maximum, so not much use really except maybe for Media Center compatiblilty. The upside is that it encodes many times faster than WMV9, even with all settings on maximum.

WMV9/VC-1 is pretty good for HD stuff and DVD conversions, it compares pretty well to x264, but like x264 it can take forever to encode depending on your settings.

[neomaine]

Bman,

Generally, you have to choose what is more important to you: File size or quality. Once you decide which is more important you then decide the enocoding path you want.

- If quality is more important, use a constant quality setting that gets the quality you want. From here, you can lower your level of quality for smaller size until you get that sweetspot. Usually, once you find the CQ that works for you, you just keep it.

- If file size is more important, use a lower avg bitrate. Then, keep increasing your bitrate until you find the quality you want until the file gets larger then you'd like.

I started out as a bitrate kind of guy. Put alot of work into it (1-pass, 2-pass, tweak avg...etc, etc...) and settled with an avg bit rate that worked most of time. Once I started playing with CQ, I found that I could always get the quality I wanted and found that the size, though variable, was usually acceptable.

In the end, I decided that quality was more important then size and stick to CQ settings. Though I usually use DIVX, and now playing with H264, I would imagine the same concept works across different codecs.