[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 
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