[mythtv-users] MPEG2 Editing

[Joseph A. Caputo]

Ed Wildgoose wrote:
> 
>>
>> 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.  

Ah, yes, should have mentioned... interested in Linux-only solutions.

> 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.

Thanks for the explanation... I think re-quantizing is what I want. 
I've already got a 480x480 MPEG-2 (which is SVCD resolution); I just 
want turn down the bitrate.

> 
> 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!

Yeah, dvdrhelp.com is great, but tends to be rather windows-centric. 
Actually, the website is rather platform-neutral, but since the 
overwhelming majority of tools tend to be Windows...

Thanks!

-JAC