Constant quality with "H264 [.MP4] mencoder"

[kaz219]

Hi,
I'm still trying the constant quality. Does anybody else out here use it?
Here is the ffmpegX command I used:

/Applications/video/ffmpegX.app/Contents/MacOS/ffmpegX -psn_0_9830401
/Library/Application Support/ffmpegX/mencoder /Users/me/Desktop/video/video.VOB -ovc x264 -nosound -ni -sws 1 -x264encopts threads=2:me=4:qp_constant=26:i4x4:keyint=120:cabac:deblock:nob_adapt:bframes=1:psnr -ofps 25 -vop scale=704:400,crop=702:576:10:0,pp=0x33,harddup -of rawvideo -o /Users/me/Desktop/video/video.VOB.ff.264

and here is the result (so far):

Pos: 448.7s  11219f ( 3%)   3fps Trem:1752min 353mb  A-V:0.000 [259:0]

I don't understand how 259kbps could correspond to a qmin of 26 in this case. I know that the first minute of the video is almost entirely black, but that's all. So, at 448.7s, the bitrate should be much higher, shouldn't it?

This is what I mentionned in another post. Sometimes the constant quality qmin=26 leads to bitrates like 1900kbps for a video around 700x400, sometimes to what I mention here.

Anyway, I'm gone to wait for this to finish, and then watch the result.

Regards,

[kaz219]

I was tempted to just remove my post, because I've been talking too fast, but then I thought it could be usefull to other people.

So, here is the deal: the video ended up with a 400kbps bitrate, but the quality was very good (global PSNR 42). The video was just old, and the sharpeness was quite low, so the encoding was able to achieve a very high compression (10 times), having constant quality and qmin=26 (qmax=standard value).

[|bond|]

constant quant as you seem to use doesnt mean constant quality

[kaz219]

ok, so what does mean "constant quant"?

[kaz219]

Ok, so after reading this, I understand that constant quantizer is different than constant quality.

So I would like to know if ffmpegX is going to include this possibility using mencoder or x264 (I still don't really get what's the difference between x264 and mencoder H.264 in the presets)? Is it planed, and if yes, when? If it's not planed, is there a technical reason?

Thanks a lot for any answer

[kaz219]

To be more precise, I'm talking about the --crf option of x264. This seems to be real — at least subjectively better — constant quality.

I would be great to have this option in ffmpegX!

[kaz219]

And on mencoder featuring x264, it would be the -qcomp parameter, as I read here.

Hope it helps.

[|bond|]

mencoder is simply a wrapper for libx264, as ffmpeg is too or the tool from the x264 project itself