[MEncoder-users] Compression too great, bitrate too low on detelecined deinterlaced mpeg2video

[Reimar Döffinger]

On Wed, Dec 31, 2008 at 02:56:35PM -0600, Laine Lee wrote:
> Replacing the vbitrate specification with
> vqscale=2 in a command with no other change resulted in a lower bitrate
> which was comparable to what I was getting before making the changes to the
> vbitrate and dia-predia values. If there's another way that vqscale should
> be used in a command line similar to this, please let me know.

-lavcopts vcodec=mpeg2video:vqscale=2
no any other encoder options.

> One thing that baffles me is that the turbo option for the first pass not
> only decreased the bitrate, but it resulted in 1 of every 15 frames (my
> keyint specification is 15) being rendered with extreme blockiness in
> certain passages whether or not I included the keyint option among the lavc
> options in the first pass command string. To eliminate these unwanted
> results, I omitted the turbo option. There was a detriment to encoding time
> of course, but the bitrate went up, and the blocky 15th frames disappeared.

That is in the final video? Or have you been looking a the video after
the first pass? How the video looks after the first pass is
_irrelevant_, which is why you are often supposed to encode it into
/dev/null

> Possibly the most serious concern for me, though, is that encoding results
> for brief excerpts of the video (a minute or two) differed significantly
> from the results for the same passages when encoded with the entire file
> (110 minutes). Several of the results I am reporting here were only
> confirmed after encoding the entire 110 minutes of video several times.

That's the whole point of doing two-pass encoding, allowing the encoder
to distribute bits as it considers appropriate all over the video.