transcoding question (xvid)

[acheyne]

I've been playing around with getting GBPVR to auto-transcode my recorded tv. I've found the section in the config file for configuring this, but can't seem to get the output I want.

What I'd like: - same or close quality I have with the mpeg-2 that comes off the hauppauge card, but a smaller file size.

The default settings for ffmpeg give a fairly blocky output.

Does anyone have some settings that will do this? I dont care if it takes a while for the processing to happen - I just want the final output to look good and take up less space on the drive.

Thanks!
Andrew

[pBS]

here's one to try....adjust the -qscale number to your preferences...

Code:

<Conversion name="Make DVD ready"  cmd=" -y -i {SOURCE_FILE} -sc_threshold 1000000000  -flags +cgop+ildct -target ntsc-dvd -f dvd -qscale 5 -vcodec mpeg2video -acodec mp2 -ab 128 {DEST_FILE}" targetExtension=".new.mpg" />

-qscale 2 = highest qual./big files 16=lowest qual/small files

that is if you want dvd compat. output..
for divx, same principle, constant quality gives constant results, but some files will be bigger than others..

with mpeg4, youll have to play with it, and xvid or .264 will be your best bet, tho very slow..

[zehd]

Code:

<Conversion name="Make DVD ready"  cmd=" -y -i {SOURCE_FILE} -sc_threshold 1000000000  -flags +cgop+ildct -target ntsc-dvd -f dvd -qscale 5 -vcodec mpeg2video -acodec mp2 -ab 128 {DEST_FILE}" targetExtension=".new.mpg" />

-qscale 2 = highest qual./big files 16=lowest qual/small files

+cgop is closed gop, but I haven't been able to find what it means or what it does...

+ildct and I think this is for interlace, But I don't know why you have it...

I'd love to know more about this...

[mikeh49]

I found that replacing the "-b 1250K" Xvid conversion parameter in the <CustomFFmpegConversion> section of config.xml with the -qscale parameter mentioned above worked pretty well. (The -b 1250K parameter specifies a constant bit rate of 1250K which doesn't seem to be high enough for good quality.) With a qscale of 5 I could not tell the difference from the original MPEG. I raised the value to 7.5 to get a smaller file size and still could not detect a decrease in quality. I'm monitoring the file size of the conversions and the picture quality with the idea of going back to the 5 setting. This is using the TRANSCODE button on the Video Library menu, and selecting the Xvid conversion.

I'm also using the Xvid decoder from the main Xvid site, if that makes a difference.

[acheyne]

Thanks for the responses. I'm going to try this out. I've been working with and around encoding for a couple of years now from a software development perspective, and I still find all of the terminology confusing and archaic.

I ended up having to download some torrents of shows because the default xvid transcode settings that come with GBPVR made the transcoded shows unwatchable. That's not a slight at GBPVR, but it might be worth it if someone could provide sub with some new settings for those config.xml blocks to make them more usable out of the box?

[acheyne]

Cool. The qscale parameter gives me what I want. I have about the same quality image, but the files are now less than half the size of the original.

Even with a 250Gb hard drive, we were closing in on a full drive - we keep a lot of recorded shows on the machine for the kids so we have something half decent for them to watch when it's "TV time" instead of whatever happens to be on at that time.. 86 recordings of Dora, anyone?

[Slice]

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!

[sub]

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

[zehd]

<CustomFFmpegConversion>.... section of config.xml

I'm also using the Xvid decoder from the main Xvid site, if that makes a difference.

If you are changing the settings here, then the XVid decoder you downloaded doesn't enter the picture. You are only tweaking the ffmpeg.exe settings...

[zehd]

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