[MEncoder-users] new doom9 codec comparission (submission)
bugfood-ml at fatooh.org
Sun Dec 11 01:49:06 CET 2005
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:
> 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.
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