[mythtv-users] MPEG2 Editing

[Ed Wildgoose]

>
> Can anybody provide a good guide to converting high-bitrate MPEG-2 
> recordings to SVCD-compliant MPEG-2 with avidemux2?  I realize that I 
> could just set up an SVCD-compliant recording profile, but sometimes I 
> don't know I want to archive something until after the fact.  Plus, I 
> think it might result in better quality to initially encode at a 
> higher bitrate, then re-encode to a lower bitrate.  Is it necessary to 
> completely re-encode in order to lower the bitrate, or is there a 
> quicker way?  And what is 're-quantizing' that I've heard mentioned?
>

Try www.dvdrhelp.com for windows advice.  In linux, try the trancode 
website and mailing list.  There is a LOT of good stuff there - in 
particular look for the thread titled something like "big vhs to svcd 
howto".  Lots in there

In short to create SVCD's you can either use a template set of params 
from the transcode site, or else open it up in avidemux2, choose the 
SVCD resize option, and hit save...  Never done it, but it looks easy...

To avoid having to wait 24+ hours while it resizes and recompresses your 
video, (mpeg2 encoding is SLOWWWW) you can investigate re-quantizing.  
The idea here is that the slow bit of encoding is calculating all the 
mpeg2 motion vectors.  Once you have worked out which bits of the scene 
look like the previous scene, just shifted a bit, then you compress the 
remainder using a jpeg type algorithm.  The trick is to keep the motion 
vectors the same, but turn up the compression on the jpeg type 
compression bit.  Quality deteriorates only slightly, and speed is 
pretty much as fast as you can read it from disk....  Very cool. 

As far as I know though you can't resize the picture.... This likely 
means that you can't convert your recordings to svcd unless you just 
happen to have used an svcd recording size...  Hence you will need to do 
a full re-encode.

Use tools like tcrequant from transcode, or avidemux2 to do requant 
stuff.  Personally I didn't make tcrequent from the latest transcode 
work properly, but avidemux2 works ok for me. 

Under windows, use dvd2svcd to do really excellent re-encodes to svcd.  
You will need a commercial encoder from "somewhere" to use this tool 
though.  Best of breed tool though.

Perhaps someone could sketch this up into some sort of a howto for the 
website?  Do check www.dvdrhelp.com for a very good resource though!

Ed W