AutoGK and the case of the bloating avi's

GlenR · **4th April 2008, 07:03 PM**

I use VideoReDo to edit then convert my dvr-ms files to mpeg, the AutoGK to convert the mpegs to avi files for upload to my server. I use the default 75% Target Quality setting and find this gives a good balance of reduced file size and quality (at least for me).

Most of the stuff I record and convert is from the SD channels, but the other day SWMBO recorded some shows from 7HD (not telecast in SD) and wanted them kept, so I went through my standard process but for some reason the avi files were larger than the original mpegs.

I also did an small SD file at the same time at it behaved well, giving a substantially lower file size than the original.

Here's what I ended up with:

SD file
Duration - 3min 42sec
Aspect - 720x576 16:9
Audio - AC3
mpeg size - 192,431 kB
avi size - 50,304 kB (what I would expect)

HD files
Duration - 20min 11sec
Aspect - 1920x1088 16:9
Audio - AC3
mpeg size - 2,086,711 kB
avi size - 2,683,362 kB (28.6% LARGER)

Duration - 20min 23sec
Aspect - 1920x1088 16:9
Audio - AC3
mpeg size - 2,105,899 kB
avi size - 2,744,066 kB (30.3% LARGER)

All three files were done in the same batch with the same settings. Why have the HD ones increased in size?

Any ideas?

Ararat · **17th April 2008, 06:44 PM**

It has been known to happen SOMETIMES for me with SD videos, when they have bad compressibility (what comptest value did AutoGK give you?). The obvious way to slash file size would be to drop the width to something like 720 if you don't mind losing resolution.

Would it have something to do with 7 using Long GOP?

GlenR · **1st May 2008, 01:12 PM**

I take it no-one has any theories on why the files grow with AutoGK?

I appreciate that resizing to 720 will reduce the file size, and I fully expect a converted HD show to be bigger than a converted SD show, but how can the XviD files be bigger than the mpeg file?

arkay · **1st May 2008, 03:11 PM**

Could be a bug. Bitrate has the biggest effect on file size. Perhaps GK has not yet been optimised for HD encoding. Mind you. I have seen it with mencoder too. Sometimes the method of the compression given the particular type of video under very irregular circumstances can cause a larger file. You're not really compressing the file, you're re-encoding it to another format. That re-encoding generally results in a smaller filesize but isn't necessarily guaranteed.

Cheers,

Arkay.