transcoding question (xvid)

[acheyne]

Post the final xvid settings you guys are happy with and I'll update the default profiles for the next release.

Thanks, sub!

[acheyne]

So, if you want to use a qscale value, you should remove the bitrate (-b) value?

I believe the qscale value implies a varying bitrate so that the overall quality of the encoded video stays constant. So, during high action scenes, the bitrate will go up so that less detail is lost, but during scenes with little movement, the bitrate will go down.

I have no idea what happens if you specify both - potentially the (-b) value gets treated as a max value so you wont get exactly the results you want?

[acheyne]

This is what I'm using now:

Code:

<Conversion name="XviD-SmallFiles" cmd="-y -i {SOURCE_FILE} -f avi -ab 224 -ac 2 -acodec mp3 -vcodec mpeg4 -qscale 6 -vtag XVID {DEST_FILE}" targetExtension=".avi">-y -i {SOURCE_FILE} -f avi -ab 224 -ac 2 -acodec mp3 -vcodec mpeg4 -b 2000k -vtag XVID {DEST_FILE}</Conversion>

Basically, I just replace the -b parameter with the -qscale parameter and found a value that worked for me.

I have not tried any of the other encoders outside of XVid.

[acheyne]

Excellent, be trying this tonight myself, was never happy with the xvid transcode quality and whenever I went at that line I always messed things up!

Ahh, the kids shows, once they learn to say "Daddy can you record this" your hard drive will never be the same again!

It's already bad enough with my wife filling things up with Oprah and the Gilmore Girls!

[dneprrider]

86 recordings of Dora, anyone?

69 episodes of JAG I still have to watch.... these numbers have the making of an interesting thread. Who has the most episodes of something saved?

[mikeh49]

Sub, I'd recommend changing "-b 1250K" to "-qscale 5" in the Xvid line of config.xml. (I also changed -vcodec to "mpeg4" because I saw that somewhere on a forum, not sure it makes any difference.) This should take care of user quality concerns (but maybe create file size concerns.) Using qscale, the converted file size varies quite a bit, apparently depending on input file content. (I generally record at your "High" setting.) I've found it difficult to predict a "compression ratio." But, I'm happy with the recovered disk space and the picture quality. Maybe someone else has a constant bitrate value that provides a good picture; qscale did the job for me, so I didn't do any further investigation.

I made the previous comment about using the Xvid decoder in case that had any influence on picture quality. I use the Purevideo decoder for mpeg2 files.

[sub]

Ok, thanks for the info guys.

[zehd]

Thanks to this thread I've been playing with the qscale instead of bitrate too.

I have noticed while 2 being the best, and 31 being the worst , the lowest that I could go is 7. That was a notch above 8 where I started to see blocking.

Now, on a TV it's possible that one could go even lower, but on a computer monitor, I think 7 gives great compression.

I have added support for this parameter into ZProcess, and it even shaves a couple seconds off, making the transcode go even faster...

This is really cool. I really glad you guys started playing with this...

[HtV]

I have noticed while 2 being the best, and 31 being the worst , the lowest that I could go is 7. That was a notch above 8 where I started to see blocking.

Since when is 7 above 8? It was a bit confusing but I got it at last.

[acheyne]

Thanks to this thread I've been playing with the qscale instead of bitrate too.

I have noticed while 2 being the best, and 31 being the worst , the lowest that I could go is 7. That was a notch above 8 where I started to see blocking.

Now, on a TV it's possible that one could go even lower, but on a computer monitor, I think 7 gives great compression.

I have added support for this parameter into ZProcess, and it even shaves a couple seconds off, making the transcode go even faster...

This is really cool. I really glad you guys started playing with this...

I run GBPVR into a 27" CRT TV and qscale at 7 was too blocky. 6 seemed to be a good number.. still some jaggies once in a while in action scenes, but no more so than you see in most DVD's.

I'm glad we got some answers in this thread. Before posting, I tried searching through the forums and found several threads that started out asking basically the same question, but never went anywhere!