[MPlayer-users] 3 pass encoding, resulting file 5% under when cropping

[Andrew Worsley]

  Hi, I'm trying to encode a DVD and crop out the black borders using the 3
pass method and the divx4 library. The cropping doesn't make the slightest
bit of difference to the estimate for the bitrate I need *but* the generated
file (after the 3rd pass) is only 667Mb instead of the promised 700Mb. The
2nd pass gave an avi of the right size so I have some questions:

  1. Have I miss used the commands and some how done 2 pass encoding and
  "over-encoded it or something" e.g. cropping twice or something silly.

  2. Is there a bug/problem in the estimating code when you do additional
  processing of the image (sub-titles/cropping?)

  3. Is there a way to work out what I can increase the bitrate up to get a
  full 700Mb worth of file on the 2nd pass? 

  4. What is the correct procedure with the additional options to mencoder
  when using multiple passes:
      (a) always use the full set of filter options (cropping/dvd
	     lanaguage/subtitle extraction/...) on each pass

      (b) Only bother on the 1st (2nd/3rd) pass?

  5. Is there any problem with restarting the encoding from any particular pass
  using the files from previous runs. e.g. starting from pass 2 using
  frameno.avi file, starting from pass 3 using divx2pass.log et cetera?

  6. Any comments on how much encoding the subtitles like this will burn me
  in quality? The other option was to go for the english language audio and
  no sub-titles.

  7. Is there a way to get the cvs release of the libavcodec library from
  behind a firewall (which appears to block cvs over the net access)?

* I include command summary for people's information:
* -vop cropdetect on the original DVD I get:

 crop area: X: 0..719  Y: 70..504  (-vop crop=720:434:0:70) 23.3% 51 0 0%

* .avi generated with:

mencoder -slang en -alang zh -dvd 1 -ovc frameno -o frameno.avi -vop crop=720:434:0:70

 * and gives:

Recommended video bitrate for 650MB CD: 615
Recommended video bitrate for 700MB CD: 676
Recommended video bitrate for 800MB CD: 797

Video stream:    0.800 kbit/s  (99 bps)  size: 690888 bytes  6908.960 secs  172724 frames

Audio stream:  159.773 kbit/s  (19971 bps)  size: 137993352 bytes  6909.480 secs

  * which is identical to that with out the -vop crop stuff.

  * pass 2 done with:

mencoder -slang en -alang zh -dvd 1 -o crouchingTiger.avi -oac copy  -pass 1 -ovc divx4 -divx4opts br=676 -vop crop=720:434:0:70

  * This generates a very nice looking .avi file very close to the 700Mb size
  * for the bitrate I choose
 
mencoder -slang en -alang zh -dvd 1 -o crouchingTiger.avi -oac copy  -pass 2 -ovc divx4 -divx4opts br=676 -vop crop=720:434:0:70

   * This gives the 667Mb file - doesn't appear to be quite as good quality
   * (perhaps my imagination??)

	Andrew