[HWK]

Originally Posted by HWK

videofan3d, this is my second time and I noticed VBR algorithm undersize files as much as 40 % and I am using pacific rim as a example. While I expected file size to be 18GB+, it was around 10 GB or so for both stream. I have provided command line and specify bitrate in Kbit/s

[update1]

I decided redo and change bitrate to 28000, after about 55% done (calculate from number of frames done, from total frames) total size is 7.10 GB for both stream.

Originally Posted by HWK

I think I have figured out my problem, It has to do with Kilobytes and kilobits. When calculating for disc use Kilobytes, which I didn't. Where encoder wants them in Kbit/s dumb error.

Spoke to soon, error is still there, but I think I have manged to get bottom of this and that is encoder help fine need some work, instead kilobits unit it expect bit-rate to be in Kilobytes. When I enter 60000 KBps (kilobytes per second) media info report correctly about max bitrate for combine avc and mvc to be 60 MBps (megabytes per second) which can be confirmed by reading values from original and another mvc encoder.

I also tried higher and lower values for bit-rate, but for me it is doing undersize. For example I use 28000 on higher side along with 60000 max, where after 55% it is only 7.10GB for both stream and with default bit-rate of 19540 expected target size is 18.62GB combined.

Originally Posted by HWK

I re-ran test and I can confirm some kind of saturation is happening in my case. I expect final output to be around 29GB or higher. However when encoder finished it was just above 16GB for both files.

I encoded with bitrate 30298Kbps, with max at 60000Kbps. However bitrate scanner tell different story altogether.

Source: Pacific Rim

Currently, I am re-doing the test with average bitrate and max bitrate at same value and it is set to 60000Kbps. It would be interested to see what happens with output.

Originally Posted by HWK

Thanks, for the result. Good to know I am not the only one. My guess VBR need some work and in my case difference is huge though.

Originally Posted by videofan3d

Regarding bitrate:

parameters for -vbr and -cbr are passed to Intel Media libmfxsw32.dll library, which controls the whole encoding.

Intel documentation specifies that it is in Kbit/s, defined as unsigned 16-bit number, where 1 kbit means 1000 bits.

Regarding "underbitrating" for VBR: I can imagine why it happens.
Intel Media is single pass encoder. When you specify -vbr 16000 24000, it means that maximum bitrate is 24000 Kbit/s which can be easily controlled. But average 16000 Kbits/s is a bit complicated issue for encoder, because single pass encoder cannot predict complexity of the videoscene, it can only evaluate current frame or maybe current GOP. So to achieve overall VBR on given value 16000 Kbits/s is only best guess for it. Therefore encoder uses rather lower bitrate whenever possible in order to prevent potential excess in future more complex scenes. As result it may happen that overall average bitrate is lower than specified.

Originally Posted by HWK

I understand your point of view, but I use different mvc encoder and use one pass on that as well and it is able to meet target size. I can't complain it is certainly better to have two mvc encoder than one.

[update1]
I just finished encoding on 60000 bitrate and so far my findings are file size is half of projected. For example I expected to be around 56GB, but final turn out to be around 27 GB.

Solution for me double the bitrate for example if I want 1000, write 2000 in encoder file and my final output would be of 1000 Kbps. In the meantime I would also try few more disc as well and see if it is some kind of pattern which I can repeat.

I finally figured out why I was having issues with size when doing VBR. It was not fault of encoder but mine instead Basically it is the workflow which I am using is issue over here.