Best settings for equal quality 720x480 mpeg2 to Divx?

[dvasco]

What are the best settings for equal quality 720x480 mpeg2 to Divx? There are a lot of default settings and I am not sure what I need to change. Why does it crop? etc. I want the quality to be equal. I used a Home Theater default setting and I saw a lot of artifacts. Also the audio was off.

[edDV]

I'll offer a general rule for MPeg2 vs MPeg4 bitrates.

Mpeg4 will get aproximately equal quality to MPeg2 at half to one third the bitrate. However this assumes both are encoded from the same uncompressed source. Milege varies if you are re-encoding an existing MPeg2 into MPeg4.

[FulciLives]

Try using "autoGK" and set the width to a fixed 640 and see how that works for you.

Please note that "autoGK" does a compressionability test and if this turn out to be below 90% you should stop it and make the file size larger and start over.

- John "FulciLives" Coleman

[jagabo]

Best quality: 1 pass quality based, target quantizer = 1. The file probably be bigger than your MPEG2 source though.

Target quantizer = 2 will give you video that's nearly indistinguishable from the source even if you look at enlarged still frames. But the file size will still be pretty large -- a little smaller than the MPEG2 source.

Target quantizer = 3 will give a little macroblocking if you look at enlarged still frames. It won't be noticable at normal playback speeds. The file size will be significantly smaller than the MPEG2 source.

Higher quantizer values will give more macroblocks and smaller files.

[dvasco]

I'll offer a general rule for MPeg2 vs MPeg4 bitrates.

Mpeg4 will get aproximately equal quality to MPeg2 at half to one third the bitrate. However this assumes both are encoded from the same uncompressed source. Milege varies if you are re-encoding an existing MPeg2 into MPeg4.

The source is an MPEG2 from ReplayTV. 720x480 3.5 Mbps total. 192kbps audio. What is the setting needed for that? I don't want the encoding to take more than 4 hours on an Athlon 1700+. Also I am looking for a filesize at least 20% smaller than the original.

[dvasco]

Best quality: 1 pass quality based, target quantizer = 1. The file probably be bigger than your MPEG2 source though.

Target quantizer = 2 will give you video that's nearly indistinguishable from the source even if you look at enlarged still frames. But the file size will still be pretty large -- a little smaller than the MPEG2 source.

Target quantizer = 3 will give a little macroblocking if you look at enlarged still frames. It won't be noticable at normal playback speeds. The file size will be significantly smaller than the MPEG2 source.

Higher quantizer values will give more macroblocks and smaller files.

Where is the quantizer setting located? I see an encoding preset with numbers ranging from 1 to 10. It looks like I need something between 2 and 3. A good balance between quality and filesize.

[edDV]

I'll offer a general rule for MPeg2 vs MPeg4 bitrates.

Mpeg4 will get aproximately equal quality to MPeg2 at half to one third the bitrate. However this assumes both are encoded from the same uncompressed source. Milege varies if you are re-encoding an existing MPeg2 into MPeg4.

The source is an MPEG2 from ReplayTV. 720x480 3.5 Mbps total. 192kbps audio. What is the setting needed for that? I don't want the encoding to take more than 4 hours on an Athlon 1700+. Also I am looking for a filesize at least 20% smaller than the original.

I claim no expertise in Divx, so I'm taking notes here from the others.

[jagabo]

Where is the quantizer setting located? I see an encoding preset with numbers ranging from 1 to 10. It looks like I need something between 2 and 3. A good balance between quality and filesize.

You may also have to consider a few other things. All the following is based on using quality based (target quantizer) encoding (much of it also applies to birate based encoding):

If you want every frame to be encoded with the same quality disable Bidirectional Encoding. B frames are normally encoded with a larger quantizer. Disableing bidirectional encoding will make the output file larger.

Since your source isn't square pixel you will want to resize to a 4:3 frame size (eg, 640x480) or use MPEG4's display aspect ratio (DAR) setting. I don't think Divx allows you to set the MPEG4 DAR but you can add it later with MPEG4Modifier. That is, just compress at 720x480, then use MPEG4Modifier to set the DAR to 4:3. Note that not all players will support DAR so resizing may be preferable. Use the Lanczos4 filter if you use Divx's built in resizer.

As far as speed is concerned, using Encoding Mode (on the Codec tab) higher than Balanced will take longer to encode but only give slightly smaller file sizes. For example, going from Balanced to Insane may take 4 times longer to encode but only produce a 5 percent smaller file. Since we are talking about constant quality encoding both files have the same quality, the higher setting is just able to squeeze the file size a little more and still maintain that quality. As far as I can tell this setting only controls the motion search precision.

If your source is interlaced you have to consider that too. Enable the interlaced setting in Divx. Many players don't really know what to do with interlaced video though. It may not display to your liking. The other option is to inverse telecine (if possible) or deinterlace. Ypu're walking into a mine field...

If you can use Xvid instead, it will give smaller file sizes at similar settings and it supports the MPEG4 DAR properly. But again, whatever player you use may not support DAR.

[dvasco]

I just finished encoding a 30 minute show with Dr. Divx at HighDef extreme quality. The quality is decent, fillesize is 37% of original, encode time was 2 hours on Athlon 1700+ and the audio was dead on.

This was in the log:
12-12-2006 10:22:00 Info No changes to C:\DOCUME~1\Diego\LOCALS~1\Temp/Dr.DivX OSS/ddx00.xml/aud-0.mp3 are necessary

12-12-2006 10:22:01 Info [mpeg] Input #0, mpeg, from 'F:\DVD\El Cid\The Colbert Report_rtvconvert QS_cc.mpg':
12-12-2006 10:22:01 Info [mpeg] Duration: 00:29:59.3, start: 0.200000, bitrate: 3842 kb/s
12-12-2006 10:22:01 Info [mpeg] Stream #0.0[0x1e0], 29.97 fps(r): Video: mpeg2video, yuv420p, 720x480, 7413 kb/s
12-12-2006 10:22:01 Info [mpeg] Stream #0.1[0x1c0]: Audio: mp2, 48000 Hz, stereo, 192 kb/s
12-12-2006 10:22:01 Info [avi] Output #0, avi, to 'C:\DOCUME~1\Diego\LOCALS~1\Temp/Dr.DivX OSS/ddx00.xml/vid-0.avi':
12-12-2006 10:22:01 Info [avi] Stream #0.0, 29.97 fps(r): Video: divx, yuv420p, 624x464, q=2-31, 900 kb/s
12-12-2006 10:22:01 Info Stream mapping:
12-12-2006 10:22:01 Info Stream #0.0 -> #0.0
12-12-2006 10:22:01 Info [divx] codec parameters: '-bvn1 900000 -vbv 9708400,6291456,4718592 -profile=4 -dir "C:\DOCUME~1\Diego\LOCALS~1\Temp/Dr.DivX OSS/ddx00.xml/" -use_presets=1 -preset=4 -nf -thread_delay=1 -enhance_texture=1 '

[dvasco]

Correction: It was High Def Balanced, now I remeber stopping the extreme quality since it was going to take too long.

[dvasco]

Where is the quantizer setting located? I see an encoding preset with numbers ranging from 1 to 10. It looks like I need something between 2 and 3. A good balance between quality and filesize.

You may also have to consider a few other things. All the following is based on using quality based (target quantizer) encoding (much of it also applies to birate based encoding):

If you want every frame to be encoded with the same quality disable Bidirectional Encoding. B frames are normally encoded with a larger quantizer. Disableing bidirectional encoding will make the output file larger.

Since your source isn't square pixel you will want to resize to a 4:3 frame size (eg, 640x480) or use MPEG4's display aspect ratio (DAR) setting. I don't think Divx allows you to set the MPEG4 DAR but you can add it later with MPEG4Modifier. That is, just compress at 720x480, then use MPEG4Modifier to set the DAR to 4:3. Note that not all players will support DAR so resizing may be preferable. Use the Lanczos4 filter if you use Divx's built in resizer.

As far as speed is concerned, using Encoding Mode (on the Codec tab) higher than Balanced will take longer to encode but only give slightly smaller file sizes. For example, going from Balanced to Insane may take 4 times longer to encode but only produce a 5 percent smaller file. Since we are talking about constant quality encoding both files have the same quality, the higher setting is just able to squeeze the file size a little more and still maintain that quality. As far as I can tell this setting only controls the motion search precision.

If your source is interlaced you have to consider that too. Enable the interlaced setting in Divx. Many players don't really know what to do with interlaced video though. It may not display to your liking. The other option is to inverse telecine (if possible) or deinterlace. Ypu're walking into a mine field...

If you can use Xvid instead, it will give smaller file sizes at similar settings and it supports the MPEG4 DAR properly. But again, whatever player you use may not support DAR.

I finally got to a point where I can try it this way. I had already started it the with the default settings for Highdef balanced before I saw your post. Thanks for the help.

[dvasco]

Does encode time change in resizing to an even smaller size? I play it all back on a standard TV with www.GBPVR.com

[jagabo]

Does encode time change in resizing to an even smaller size?

Yes. The smaller the frame the faster it will encode (assuming other settings aren't changed).

[dvasco]

Target quantizer = 2 made a filesize almost equal to the original. Going to Target quantizer = 3 made a filesize 63% of original. The quality is not as good as I would like but it good enough and the encode time is only 70 minutes for 30 min video. Not too bad.

[dvasco]

jagabo, I am going to stick with target quantizer = 2. Now I can save 50% encode time and get better quality than the default Divx settings with a 63% filesize of original. The Divx people should learn from this. Thanks a million.

[dvasco]

Now I have to find out how to have GBPVR transcode with these settings.

[FulciLives]

Have you tried "autoGK" ?

- John "FulciLives" Coleman