[Mp4-tech] GOP concept in H.264

[Gary Sullivan]

I suggest reading the reference software manual found as document
JVT-Q042 in the 2005_10_Nice directory on the JVT document site
http://ftp3.itu.int/av-arch/jvt-site.
The standard itself does not actually include a definition of a concept
called a GOP.  When people refer to "open GOP", they are usually talking
about non-reference pictures that occur in the bitstream after an Intra
picture that are displayed prior to the Intra picture being allowed to
use pictures that precede the Intra picture in decoding order as
references for their motion compensation prediction decoding process.
You sound a bit confused about what the standard does, or perhaps it is
just a question of phrasing.  I must warn you that the reference
software is really meant for those who have a significant amount of
familiarity with video compression technology.  Regarding your confusion
over why the JM reference software might use more bits to code a video
clip than some MPEG-2 reference software, could it be that the two
encoded video clips do not have comparable decoded picture quality?
Targeting equal output video quality is a fundamental part of claims of
relative bit rate savings performance capability.
Best Regards,
Gary Sullivan
________________________________
	From: mp4-tech-bounces lists.mpegif.org
[mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of tummala kalyani
	Sent: Tuesday, November 08, 2023 8:45 AM
	To: mp4-tech lists.mpegif.org
	Subject: [Mp4-tech] GOP concept in H.264
	Hi All,
	I would like to know about GOP concept in H.264. In JM encoder
config file there is a parameter "support for open GOP". How can I use
this? I tried to 1-enable and 0-disable options. But I don't find any
difference. 
	There is provision to set I frame distance and number of B
frames. When I treid to set number of B frames more than 0 , it gives me
an error message saying that  "Number of B frames should me more than
frames skipped in the input". What is the use of Frames skipped
parameter in the encoder.cfg file in JM?
	I need bitrate vs psnr comparison graphs for H.264 codec and
MPEG-2 codec. For that I am running JM and MPEG-2 reference softwares
with foreman.yuv as input video. I found that for baseline and main
profiles H.264 codec output file size  is double to MPEG-2 file size. I
use this filesize to calculate bitrate( filesize * (frame rate / total
frames)). But according to specs. H.264 codec bitrate should be half to
that of MPEG-2. But I am getting in reverse. I am confused by this. I
think I have not understood it properly. Can some one explain me this
clearly?
-------------- next part --------------
An HTML attachment was scrubbed...
URL: /pipermail/mp4-tech/attachments/20051109/f89a301e/attachment.html