[mythtv-users] 68% filesize increase after transcode!

[Dave Sherohman]

On Sat, Sep 24, 2005 at 10:51:52PM -0600, Greg Grotsky wrote:
> Dave, I tried transcoding the same episode to MPEG4 and it came out 40%
> larger than the original MPEG2 transmission.

That's certainly odd...  The only things I can think of are that
either it's something to do with your working (IIRC) working with HD
or else your incoming video stream is a much more highly-compressed
mpeg2 than that produced by my PVR-500's encoder.

> I don't know why anyone would
> use these methods if they want to keep their videos the same dimensions as
> they are broadcast, since it looks like they actually ballon in size instead
> of shrink. :( I guess if I was scaling them down as well I'd see a size
> decrease but is it worth it?

I'm not resizing.  My video source is analog cable and both the
original mpeg2 capture and the transcoded version (whether RTjpeg or
mpeg4) are 480x480.

> Both the 68% increase and 40% increase were seen using the default settings
> for both RTJPEG and MPEG4 screen settings.
> 
> Are you using the default settings?

Initially, yes.  After the initial test, I turned on interlaced DCT
encoding and interlaced motion estimation (simply because I believe
my video source to be interlaced and these options say "you probably
want this when encoding interlaced video") and observed no
significant change in resulting file size.

-- 
The freedoms that we enjoy presently are the most important victories of the
White Hats over the past several millennia, and it is vitally important that
we don't give them up now, only because we are frightened.
  - Eolake Stobblehouse (http://stobblehouse.com/text/battle.html)