[x264-devel] Re: [Mohsen Shaaban <mmm5554 at cacs.louisiana.edu>] RE: Re: Using I-frame instead of IDR

[Mohsen Shaaban]

Hello Liwei,

 

Actually what I wanted to do is to change the quantization parameter Qp just
to see the effect of the requantization error on the PSNR (like in the
paper). I already managed to do that by overwriting the rate control
computation n the reference software.

Thanks for your reply anyway.

 

Regards,

 

Mohsen Shaaban

 

   _____  

From: x264-devel-bounce at videolan.org [mailto:x264-devel-bounce at videolan.org]
On Behalf Of jogging song
Sent: Friday, November 17, 2006 8:08 AM
To: x264-devel at videolan.org
Subject: [x264-devel] Re: [Mohsen Shaaban <mmm5554 at cacs.louisiana.edu>] RE:
Re: Using I-frame instead of IDR

 

Hi, Shaaban 

      I haven't caught what you said.

First, you want to transcode mpeg2 bitstram to h.264 bitstream.
Second, the paper introduced an method which can reduce bit-rate of mpeg2
bitstream in frequency-domain,
    In the paper, the author just changed QP to do bit-rate reduction and
didn't use rate control. 
Third, you hope to see the effect of requantization error.
    Bitrate reduction will cause quality degrade which can be expressed with
PSNR.
    You mean you want to do bit-reduction with rate control?
Best Regards. 
Liwei Song 

 

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----- Forwarded message from Mohsen Shaaban <HYPERLINK
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From: Mohsen Shaaban <HYPERLINK
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To: HYPERLINK "mailto:x264-devel at videolan.org"x264-devel at videolan.org
Subject: RE: [x264-devel] Re: Using I-frame instead of IDR 
Date: Thu, 16 Nov 2006 12:51:31 -0600
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Hello Loren,

First, I'm a member of x264-devel but I do not know how to post questions
from within the x264-devel mailing list. Can you please tell me how to do
that?

Second, I have a question about H.264 transcoding from MPEG-2 bitstream, I
hope you can help me.

I want to do some experiments on the MPEG-2 bitstream before Transcoding, so
I want to see the effect of requantization error on the stream and I read in

one paper that you can do that by having a fixed triplet quantization
scaling (fixed scaling value Qi, Qp, Qb) and my question is there any
feature in MPEG-2 TM5 reference software that you can change to do that or 
one have to change the rate control algorithm in there?

I attaching the paper for your reference (experiment shows in fig. 3 in the
paper)

I hope you have an answer or a guide for me to follow.
I appreciate it and thank you. 

Mohsen Shaaban
PhD Student in Computer Engineering
The Center for Advanced Computer Studies
University of Louisiana at Lafayette

-----Original Message-----
From: HYPERLINK
"mailto:x264-devel-bounce at videolan.org"x264-devel-bounce at videolan.org
[mailto:HYPERLINK
"mailto:x264-devel-bounce at videolan.org"x264-devel-bounce at videolan.org]
On Behalf Of Loren Merritt
Sent: Wednesday, November 15, 2006 10:42 PM
To: HYPERLINK "mailto:x264-devel at videolan.org"x264-devel at videolan.org
Subject: [x264-devel] Re: Using I-frame instead of IDR

On Wed, 15 Nov 2006, Axel Gunter wrote:
> Loren Merritt wrote:
>> On Wed, 15 Nov 2006, Axel Gunter wrote:
>> 
>>> I noticed all the I-frames introduced by the x264 code were IDR Access
>>> Units. Is there a way I can have non-IDR I-frames in x264 encoding?
>>
>> No. Why do you want non-IDR I-frames? The only reason I can think of is 
>> open-GOP B-frames, which x264 also doesn't do.
>
> I guess the compression would be better if the frames following the IDR or

> I-picture could use frames temporally before the IDR/I-picture since they 
> have more reference frames to chose from. Since IDR forces a decoder
> reference buffer flush, this isn't possible. Correct me if I am wrong.

In that case, look at --min-keyint. If a scenecut is too close to the 
previous IDR (default: 25 frames) it gets encoded as a non-IDR I-frame.
Note that this is not optimal, but the metric that would really optimize
for compression ratio isn't possible to measure in 1 pass, and I haven't 
written a 2 pass scenecut/IDR algorithm yet.

--Loren Merritt

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