[M4IF Technotes] RE: MPEG 4
Mariano Padilla
mpadilla sdi-media-usa.com
Fri Oct 19 10:41:48 EDT 2001
Again, I thank you all for your comments. Hence, if someone on the list can
answer my below questions.
Thank you much. If you do have the time to elaborate on the strict
Timestamps. Our concern is that when we provide for an MPEG-4 video time
specific "Subtitle Stream" which is controlled by a navigation file
containing time stamps for cue in and cue out, the temporal difference from
an "outside" graphic, in this case the subtitle superimposed on the Mpeg-4
video, can it create the same effect as the DVD MPEG-2 standard? With DVD
there is a variance of approximately 4 to 10 frames or more in some
instances. In NTSC, being 30 fps, it's a bit difficult to notice, but on
PAL at 25 fps it is a bit more noticeable. We've been experimenting also
with MPEG-4, and since it is not as accurate as MPEG-1 I-Frame, we notice
that a) when going back it does not stop on the exact frame, usually
re-renders the frames and you can visually see the re-rendering of frames.
b) slow playback, with sound, is extremely jerky and looses track where it
is, hence it needs to re-render the frames. Are these behaviors part of the
internal time correction as well as just the "de-compression" of the frames?
Would these behaviors affect time cueing of non-internal MPEG-4 objects?
For example, I have a graphic that is to be superimposed on a video at
exactly 00:23:20.10, would the 10th frame be a reference frame or would it
have to "de-compress" and generate from reference frames and how would this
affect the external temporal synch? Your e-mail below says the MPEG-4
timestamps can be as accurate as I wish, in this case I would need it to be
down to the frame, is this possible? Would I need to create the subtitle
stream of external tiffs as MPEG-4 BIFS in order to achieve the frame
accurate sync?
Mariano J. Padilla
Director of IT/R&D
SDI Media USA
T 323-602-5406
F 323-602-5450
www.sdi-media-usa.com
-----Original Message-----
From: Rob Koenen [mailto:rkoenen intertrust.com]
Sent: Fri, October 19, 2023 9:34 AM
To: 'Mariano Padilla'; 'Michelle Y Kim'
Cc: Rob Koenen; Scott Rose
Subject: RE: MPEG 4
I second Michelle's proposal to send to the list.
However, oit looks to me as if your issue is with the
implementation you are using, not with the standard.
Jerky playback is not something that is built into MPEG-4.
Rob
-----Original Message-----
From: Mariano Padilla [mailto:mpadilla sdi-media-usa.com]
Sent: Friday, October 19, 2023 9:25 AM
To: 'Michelle Y Kim'
Cc: Rob Koenen; Scott Rose
Subject: RE: MPEG 4
Thank you much. If you do have the time to elaborate on the strict
Timestamps. Our concern is that when we provide for an MPEG-4 video time
specific "Subtitle Stream" which is controlled by a navigation file
containing time stamps for cue in and cue out, the temporal difference from
an "outside" graphic, in this case the subtitle superimposed on the Mpeg-4
video, can it create the same effect as the DVD MPEG-2 standard? With DVD
there is a variance of approximately 4 to 10 frames or more in some
instances. In NTSC, being 30 fps, it's a bit difficult to notice, but on
PAL at 25 fps it is a bit more noticeable. We've been experimenting also
with MPEG-4, and since it is not as accurate as MPEG-1 I-Frame, we notice
that a) when going back it does not stop on the exact frame, usually
re-renders the frames and you can visually see the re-rendering of frames.
b) slow playback, with sound, is extremely jerky and looses track where it
is, hence it needs to re-render the frames. Are these behaviors part of the
internal time correction as well as just the "de-compression" of the frames?
Would these behaviors affect time cueing of non-internal MPEG-4 objects?
For example, I have a graphic that is to be superimposed on a video at
exactly 00:23:20.10, would the 10th frame be a reference frame or would it
have to "de-compress" and generate from reference frames and how would this
affect the external temporal synch? Your e-mail below says the MPEG-4
timestamps can be as accurate as I wish, in this case I would need it to be
down to the frame, is this possible? Would I need to create the subtitle
stream of external tiffs as MPEG-4 BIFS in order to achieve the frame
accurate sync?
I thank you all for your comments.
Mariano J. Padilla
Director of IT/R&D
SDI Media USA
T 323-602-5406
F 323-602-5450
www.sdi-media-usa.com
-----Original Message-----
From: Michelle Y Kim [ mailto:mykim us.ibm.com <mailto:mykim us.ibm.com> ]
Sent: Fri, October 19, 2023 9:21 AM
To: 'Mariano Padilla'
Cc: Rob Koenen; Scott Rose
Subject: RE: MPEG 4
Mariano,
Since I don't know what kind of problems you're trying to solve, I can only
offer you the following very general response, and will have to echo Rob
and ask you to bring this to the reflector.
If you want to achieve frame-level synchronization of subtitles and video,
and if the video delivery is reliable, then you can achieve synchronization
without FlexTime. You can simply align video timestamps to those of BIFS
that contain subtitles. Note that presently MPEG-4 does not support text
streams. Text in MPEG-4 is delivered in BIFS as timed insertions and
deletions, where the timestamps can be as accurate as you wish. The level
of synchornization you can from MPEG-4 is at a finer granularity than SMIL
if you're coming from the SMIL experience.
But if the video delivery is non-deterministic, then FlexTime is a technic
you can use, which I can help you with, as I understand the nature of your
question better.
Regards,
Michelle
Michelle Y. Kim, Ph. D.
Manager, Composite Media Technologies
IBM T. J. Watson Research Center
30 Saw Mill River Road, Hawthorne NY, 10532
mykim us.ibm.com
phone: 914-784-7709, fax: 914-784-7455 (tie: 863-7709)
Rob Koenen <rkoenen intertrust.com> on 10/18/2001 12:43:01 PM
To: "'Mariano Padilla'" <mpadilla sdi-media-usa.com>, Rob Koenen
<rkoenen intertrust.com>
cc: Scott Rose <srose sdi-media-usa.com>, Michelle Y Kim/Watson/IBM IBMUS
Subject: RE: MPEG 4
Again I suggest that you ask these questions on the list.
But I copy Michelle Kim of IBM - there is no better expert
on flextime to be found.
Rob
-----Original Message-----
From: Mariano Padilla [ mailto:mpadilla sdi-media-usa.com
<mailto:mpadilla sdi-media-usa.com> ]
Sent: Thursday, October 18, 2023 9:38 AM
To: 'Rob Koenen'
Cc: Scott Rose
Subject: RE: MPEG 4
Rob,
Thank you. I will subscribe. Specifically we are wondering the
synchronization of subtitles on MPEG 4 stream. In the overview, written
by you, in section 8.3.2, 'The FlexTime model allows the content author to
express synchronization among MPEG-4 objects with streams or stream
segments, by assigning temporal relationships among them.' then the
following questions:
1) Are subtitle streams to be synchronized considered MPEG objects?
2) If the subtitle streams to be synchronized are MPEG objects, do
they have to behave according to the SMIL text guidelines in section 4.2.2
of your overview?
3) If 2 above is true, then does SMIL used in MPEG4 allow milisecond
or frame-accurate synchronization with the video?
4) If there is no text/SMIL synchronization of multinational
subtitles, how can synchronization of external images be achieved? Is it
similar to the MPEG2/DVD model?
Thanks again,
Mariano
-----Original Message-----
From: Rob Koenen [ mailto:rkoenen intertrust.com
<mailto:rkoenen intertrust.com> ]
Sent: Wed, October 17, 2023 5:17 PM
To: 'Mariano Padilla'; Rob Koenen
Cc: Scott Rose
Subject: RE: MPEG 4
Mariano,
you can ask me but I am not the best source for technical
details. I could forward your questions to experts. I would suggest,
however, that you subscribe yourself to the technotes mailing list
of the MPEG-4 Industry Forum (this is a public list) and ask your
question there. Then I will monitor that you indeed do get an answer.
See http://www.m4if.org <http://www.m4if.org> and in particular
http://www.m4if.org/public/publiclistreg.html
<http://www.m4if.org/public/publiclistreg.html>
Hope this helps,
Rob
-----Original Message-----
From: Mariano Padilla [ mailto:mpadilla sdi-media-usa.com
<mailto:mpadilla sdi-media-usa.com> ]
Sent: Wednesday, October 17, 2023 5:11 PM
To: 'rob intertrust.com'
Cc: Scott Rose
Subject: MPEG 4
Rob,
I got your e-mail address form the MPEG-4 standards article and I
have a couple of questions, specifically regarding section 8.3 'FlexTime'
and synchronization of subtitles. Can I address these questions to you,
or if you have someone else that can answer them for me? Please advise.
We at SDI Media USA specialize in Theatrical, DVD, Home Video and
broadcast subtitles and captions for over 40 languages. Naturally we are
looking at how subtitles are synchronized in MPEG-4.
I thank you in advanced for the time spent.
Mariano J. Padilla
Director of IT/R&D
SDI Media USA
T 323-602-5406
F 323-602-5450
www.sdi-media-usa.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: /pipermail/mp4-tech/attachments/20011019/c8e0e6b3/attachment.html
More information about the Mp4-tech
mailing list