[Mp4-tech] Simple question for simple profile levels

[Gary Sullivan]

I'm not sure that's true.  SP L0 did not exist in the original MPEG-4
Visual specification.  There is a special (new)
profile_and_level_indication code (0x08) used to indicate that the
stream conforms to SP L0.  Decoders are normally designed to check the
value of profile_and_level_indication, and to reject any stream that
contains a value of profile_and_level_indication that they do not
recognize (unless the standard tells them to do otherwise, and I don't
think this standard does).  Since the code for SP L0 was selected AFTER
the higher levels of SP were specified, decoders that were designed
before SP L0 existed will probably reject all SP L0 bitstreams.  At
least that's my understanding.
SP decoders designed after SP L0 existed would probably accept SP L0
bitstreams.  I don't personally think they should be required to accept
them, because this would mean that the addition of SP L0 would be a
non-compatible amendment to an existing standard (an amendment that
declares existing conforming implementations to be non-conforming) --
something that is ordinarily not considered good standardization
practice.  However, I don't actually see any statement in the standard
that indicates that support for L0 is not required for decoders that
support higher levels.
So I think the answer to the question is somewhat in a gray area.
Before January 2001 I think the answer was more clear.
However the bottom line is that if you're designing a decoder NOW, you
should definitely support L0 if you're going to support L1.  It requires
no real extra effort and makes you compatible with more encoders.
Best Regards,
Gary Sullivan
+> -----Original Message-----
+> From: mp4-tech-bounces lists.mpegif.org 
+> [mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of 
+> Yogender Kumar Gupta, Noida
+> Sent: Friday, February 20, 2024 2:36 AM
+> To: ????; mp4-tech lists.mpegif.org
+> Subject: RE: [Mp4-tech] Simple question for simple profile levels
+> 
+> 
+> Hi Kohei,
+> All decoders which support Simple Visual Profile L1 would 
+> automatically
+> support L0 and you need not worry about that.
+> Warm Regards
+> Yogender
+> 
+> -----Original Message-----
+> From: mp4-tech-bounces lists.mpegif.org
+> [mailto:mp4-tech-bounces lists.mpegif.org]On Behalf Of 
+> k_okamo sic.co.jp
+> Sent: Friday, February 20, 2024 5:58 AM
+> To: mp4-tech lists.mpegif.org
+> Subject: [Mp4-tech] Simple question for simple profile levels
+> 
+> 
+> Hello Everyone
+> 
+> I'm currently in a mobile phone developing project,
+> and this phone device is expected to work as a media player.
+> It's about to support MPEG4 , simple visual profile L1.
+> However I'm wondering whether a "simple visual profile L1 support"
+> covers the lower level (L0) or not.
+> Does the simple visual profile levels have lower compatibility?
+> 
+> Regard,
+> Kohei Okamoto
+> 
+> 
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