better quality with XviD than x264?

[jtarrio]

Hi all,

I've been experimenting for a while with AutoGK and MeGui to encode in XviD with MP3 (128Kbps) audio and x264 with AAC (96 Kbps) audio respectively. I've encoded the same movie (The Day After Tomorrow) with both programs I have found that I get a better quality with XviD than with x264.

Here's a link to download two clips extracted from the output so you can compare:
http://www.yousendit.com/transfer.php?action=download&ufid=F22B88EE6EBCEAFC&rcpt=juan.tarrio@wanadoo.es
http://www.yousendit.com/transfer.php?action=download&ufid=06A22FFE6E726437&rcpt=juan.tarrio@wanadoo.es

It seems strange to me that x264 is giving worse results. I've used the HQ-Slow profile. For both encodes, I've adjusted the file size to 1/4 DVD, so in fact x264 had more "room" for video encoding as it used a lower bitrate audio.

I haven't used any special settings in AutoGK.

I would like to gather feedback to know if this is normal. I assumed that an AVC codec should give a much better quality for the same bitrate than an ASP codec...

Maybe I'm missing something as I'm a complete newbie...

Cheers...

[Awatef]

It may not relate to your question directly, but I would use Vorbis instead of AAC for 96kbps bitrates...

[GodofaGap]

I don't find the difference that shocking. Do you by any chance have post-processing enabled in ffdshow for h264 decoding?

[smok3]

what settings you used?

[jtarrio]

I don't find the difference that shocking. Do you by any chance have post-processing enabled in ffdshow for h264 decoding?

Well, I know the difference is not shocking, but I would have expected x264 to be much better quality at the same bitrate. Specially with HQ profile (12 hours encoding). However, XviD results are better for only 5 hours encoding time.

Oops! Post-processing was indeed on in ffdshow. I turned it off and it looks much better... I thought post-processing would be for improving image quality?

Well, it's good to learn new things...

Thank you all!

[DarkZell666]

Haha, yes postprocessing is indeed for enhancing the quality, however the postprocessing filter reads the current frame quantizer to determine how strong the picture needs processing.

But quantizers in MPEG4-ASP and AVC aren't the same values at all. AVC's quantizer's are logarithmic and ASP's are linear.

In the facts, XviD quant 2 looks pretty much like AVC quant 18.

Since ffdshow sees quant=18 or more when decoding AVC, it processes the picture like hell when it isn't needed.

Therefore you should disable postprocessing when watching AVC :) You're not the first one to fall for it, don't worry =)