2 pass bitrate not being met

[kersey]

Hi there,

I am trying to convert an mkv file that has a bit rate of over 2000Kps into a 2 pass 1200Kps avi file but am finding that no matter what I select the conversion is always around 950+Kps.

I have attached the properties of the mkv file, the converted avi file and my video settings in the hope that someone can explain why I can not get my desired converted bitrate.

[HuggiL]

It's because of the way that 2-pass encoding works. The first pass analyses the video and by using the results of that analysis, it optimises the bitrate in the encoding done on the second pass. So some scenes may have a lower bitrate that other scenes, in essence, your video is now a variable bitrate.
I just tried a video encoded using the same settings as you and the bitrate varied from as low as 300Kbps up to bursts of 3000Kbps in busy scenes. So I think the way 2-pass works is that it calculates the file size of the video first as if it were a constant bitrate then optimises the bitrate of each scene so that it fits into that size.

If you need to have the video at 1200Kbps, try using a single-pass encoding (constant or average bitrate should work).

[kersey]

Thanks for you reply.

I understand what you are saying and it makes sense about the bit rate varying, although on other encoding programs I have used normally when I selected a 2 pass encode it usually met the desired bit rate.

Have tried an average bit rate encode with the rate set to 1500Kps and the overall result was even lower as per screen shot...strange.

In a final attempt I tried a constant bit rate but get two errors 'Rate Mode Not Supported' followed by 'Failed to load xvid. This can be caused by the absence of the library/binary'.

Any ideas to the low average bit rate encode or the error is appreciated.

[HuggiL]

My bad about average bitrate. Seems that works similar to 2-pass (less busy scenes get lower bitrate, busier scenes have high bitrate) but it skips the analysis run so it's just not as optimised as 2-pass. As for constant bitrate, I can't get it to work with Xvid as well. MPEG4 video format works with it though.

Also, which version of MediaCoder are you using? And if you use your other encoding programs on this file, does it meet your desired bitrate?

[kersey]

Am using version 0.8.28.5585. Have just noticed there's a new update so will try that.

With an alternative encoding program using the xvid codec with the same settings I get very close to the desired output.

I converted the same file as a two pass encode @ 1200Kps and got 1190Kps.

Really don't know why mediacoder won't do the same