[Mp4-tech] Re: PCR Discontinuity Issues

[Mohit Agarwal]

Thanks Song,
I have a doubt regarding Continuity Counter(cc).
Consider the following Base case and a variant mentioned at end of mail.
<cc=0> <pcr_flag == 0, discontinuity_indicator = 0> // old system time
<cc=1>   <pcr_flag == 0, discontinuity_indicator = 1> // new system time
begin
<cc=2> <pcr_flag == 1, discontinuity_indicator = 1> //  new PCR set.
<cc=3> <pcr_flag == 0, discontinuity_indicator = 0> 
Acc to 2.4.3.5 of H.222.0 there can be a CC error in Case of PCR_PID Packet
also,but
This err will occur only in packet in which system discontinuity will occur.
What I think this CC error is totally dependent on the Network.If there are
some attenuations in the 
Network then only can a packet be dropped.This CC err can occur in any
packet.
Now consider the case when the Packet containing the new PCR set gets
dropped.Then How will
Demuxer will come to know of the new time base.Will it to wait till next
discontinuity in PCR to occur,then new 
Time base to arrive or there is some way???
<cc=0> <pcr_flag == 0, discontinuity_indicator = 0> // old system time
<cc=1>   <pcr_flag == 0, discontinuity_indicator = 1> // new system time
begin
/////////////<cc=2> packet gets dropped
<cc=3> <pcr_flag == 0, discontinuity_indicator = 0> 
Regards
Mohit
-----Original Message-----
From: Amit Upadhyay [mailto:aupadhyay neomagic.com] 
Sent: Tuesday, July 18, 2023 11:24 AM
To: magarwal neomagic.com
Subject: FW: [Mp4-tech] Re: PCR Discontinuity Issues
-----Original Message-----
From: mp4-tech-bounces lists.mpegif.org
[mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Song
Sent: Monday, July 17, 2023 7:56 AM
To: mp4-tech lists.mpegif.org
Subject: [Mp4-tech] Re: PCR Discontinuity Issues
Dear Mohit Agarwal
I think which packet contains the valid pcr value should be checked with
PCR_flag in adaptation_field. If PCR_flag set 1, the PCR can be used.
So I think that the sequence can be modified with the following.
...
    <pcr_flag == 1, discontinuity_indicator = 0> 
    <pcr_flag == 0, discontinuity_indicator = 0> // old system time
   <pcr_flag == 0, discontinuity_indicator = 1> // new system time begin
  <pcr_flag == 1, discontinuity_indicator = 1> //  new PCR set.
    <pcr_flag == 1, discontinuity_indicator = 0>  ...
Best Regards.
Song
> 
> Message: 4
> Date: Fri, 14 Jul 2023 15:54:46 +0530
> From: "Mohit Agarwal" <magarwal NeoMagic.com>
> Subject: [Mp4-tech] [MPEG2-SYSTEMS]PCR Discontinuity Issues
> To: <mp4-tech lists.mpegif.org>
> Message-ID: <004601c6a72f$bc76c680$841fa8c0 pcmagarwal>
> Content-Type: text/plain; charset="us-ascii"
> 
> Hi,
>  
> I have a doubt regarding  discontinuity indicator in the case of pcr 
> packets, mentioned in section 2.4.3.5- discontinuity_indicator of 
> H.222.0
>  
> What I interpret from the Standard is:
>  
> <valid_pcr, discontinuity_indicator = 0>  <valid_pcr, 
> discontinuity_indicator = 0>  <invalid_pcr, discontinuity_indicator =
> 1> //do not use this value  <valid_pcr, discontinuity_indicator = 1>
> //use this value  <valid_pcr, discontinuity_indicator = 0>
>    .
>    .
>    .
>  
>  
> The standard also mentions that there can be more than two packets 
> with discontinuity indicator =1.
> But the question in this case is that how does one differentiate which 
> packet contains the valid pcr value???
>  
>  
> Thanks
> Mohit Agarwal

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