[MEncoder-users] new doom9 codec comparission (submission)

[Corey Hickey]

Doom9 Feedback Hotline wrote:
>>The video you're encoding is 196160 frames long. My source is 196070
>>frames. I don't know where the discrepancy arises. Does avisynth alter
>>the length at all? Were there more than one release of The Matrix and I
>>got a different one?
> 
> 
> I don't know where the discrepancy comes from either, I guess it could be 
> caused by the way mencoder handles NTSC (pulldown and everything). 
> Considering numbers of users and Don's nack for perfection (he wrote 
> DGIndex, the standard for mpeg2 decoding on Windows), I'm reasonably certain 
> that I'm getting exactly the number of frames the source had before pulldown 
> was applied.

The source I was using was entirely progressive, so the tests I ran
didn't use any pulldown (it wouldn't have done anything).

> My AviSynth script is as follows:
> 
> mpeg2source("D:\DVDs\THE_MATRIX_16X9LB_N_AMERICA\VIDEO_TS\matrix.d2v")
> crop(0,60,-2,-64)
> LanczosResize(640,272)
> 
> So really all I do is crop away the black bars and resize
> 
> 
>>I'm fairly sure the low bitrate on the second pass is because of the low
>>bitrate on the first. As you can see, it ended up being only 479.429
>>kbit/sec. Since I found that vqscale value specifically for the source I
>>have and the target bitrate (which is unchanged), the only thing I can
>>think of is that for some reason the video you are providing to your
>>mencoder requires fewer bits to encode at that quantizer than the video
>>I tested. If you don't have a different source DVD, than perhaps your
>>downscaling lost more detail/noise than mine did.
> 
> 
> Lanczos should be as presize a resizer as it gets. What does mencoder use 
> for resizing and how does it decode the video? What kind of color space is 
> used? Going the AviSynth route I have no colorspace conversions whatsoever 
> but I don't know what mencoder does if it decodes the data from a DVD.

By default, MEncoder uses an internal copy of libmpeg2 version 0.4.0b
with slight modifications. As far as I know (just from looking at the
output messages), the video is YV12 all the way.

>>Without being able to test your source directly, I would suggest using
>>vqscale=1.5 instead of vqscale=2.15. Don't take that to be my final
>>answer, though; I'm hoping to get some insight from other people on
>>mencoder-users. vqscale=1.5 is based on looking at a graph I have of
>>quantizer vs bitrate for snow, and erring on the low side (1.8 is my
>>closest guess, but 1.5 should be safe).
> 
> 
> Well, you can use AviSynth with Wine, and decode the AviSynth script via 
> avs2yuv.. I think dgindex also works on Linux if you don't have a windows 
> box to test.

I would try to do that, but I really don't have time right now... :(
I'll see if I can tomorrow, but it might be too late for you.

-Corey