Doom10 Forum: Digital Video Discussion

I agree for the french movies. Tough to encode and tough to understand. I won't buy them anymore.
GOP 2 1 , on the above-mentioned clip, is almost on target ( and gets worse as GOP length is increased) either because of the number of B-frames or because it affects base Q.

CQ 5 with AUTOGOP 15 and GOP 15 0 leads to different bitrate but 1-pass VBR leads to identical Base Q.

Theoretical question: If I encode at CQ=10 (no interpolation)  and encode at that bitrate at 1-pass VBR, should the base Q be 10 or not .
Did a 1-pass VBR with DVD-RB . Very impressive.

Thanks

Edit: Because you liked the movie so much, here is another clip.
Issue previously reported here (but did not know about it)
http://forum.doom9.org/showthread.php?p=1147781#post1147781

Using the GUI;(max bitrate:8000 kbps) : average bitrate at CQ=2 is lower with matrix  Fox3 ( 6979 kbps) than matrix MPEG (7445 kbps). Explanation below . CQ=3 looks OK ( Fox 3 in the 7300 kbps and MPEG in the 6800 kbps ).
http://www.sendspace.com/file/jiuc4c
http://www.sendspace.com/file/wd6fnc  (demuxed)

It looks it is due to the high average bitrate of the sequence and the quantizer of the I-frame cannot stay constant (too close to max bitrate of 8000 kbps); for CQ=2 the average quantizer is much higher with Fox3 than MPEG (that explains the relationship between bitrates at CQ=2).
For Fox3, the average quantizer is 4.72 at CQ=2 and 4.52 (smaller) at CQ=3 ( with iP_factor=1 and GOP 15 0 but similar relationship with AUTOGOP).For the interpolation of Base Q, I have no clue if one should take Q=2 or Q=4.72 ( or average of I-frame quantizer).
Or go with CQ=4,7,10 (too close to CQ=2 seems to be too much affected by max bitrate).

Edit2:Really cosmetics
a) may be start GOP length at 2 (crashes at 1)
b) CQ and VBV/birate unchecked gives in the window CQ=0 (computation is made at the appropriate CQ)
c) CQ and 1-pass allowed simultaneously in GUI
d) it seems that the info message (" Very high quantizer " for example) does not appear on the log. Would be nice when batch encoding.May be base Q in the log?

Edit3: Base Q does not take into account max bitrate.
Same Base Q (5.78) for a small clip with Fox1 targeted bitrate=6 000 kbps with max bitrate 8 000 kbps or 28 000 kbps ( I know not DVD-compliant: just to show my point).
If I use GOP 15 0 , I have " right on target " with max bitrate= 28 000 kbps but 4 980 kbps with max bitrate=8 000 kbps. Same behavior ( with much less differences) at targeted bitrate of 4 000 kbps.
The file used is the one in this post.

It looks like the relationship between size and CQ (  for CQ <4  or close to the max bitrate) depends upon the compressibility of the source.Some information about it can be gathered by doing CQ=5 and 10 before. A better approximation of the behavior close to the max bitrate can be guessed for CQ=2.

@ hank315

Got more info on the 10 031 frames clip undersizing issue
http://forum.doom9.org/showthread.php?p=1375087#post1375087

Undersized with AUTOGOP 15, GOP 15 2, GOP 15 1
Right on target with GOP 15 0,  GOP 12 0
In-between for AUTOGOP 12, GOP 12 2 , GOP 12 1
All the other settings in INI do not seems to be involved ( Yes or No ) do not change the issue.

At 50 % of the encode , the average bitrate is much closer to the targeted bitrate ( and to the 2-pass bitrate at 50 %)  with GOP 15 0 and GOP 12 0.

Thanks in advance.

Is it possible that the desired values of those two values depends on CRF(22 or 26)? I was  also wondering if those values have to stay constant, or if only the values at frame 1 have to be set and if a learning process (based on spatial complexity or whatever ) would be able to adjust them to the source and the targeted bitrate.

Thanks in advance.