[Mp4-tech] Complementary Field Pairs

[Karsten Suehring]

Hi,
the behavior in case of error is outside the scope of the H.264/AVC spec.
When transmitting video in an lossy environment, you should be using a 
transport protocol like e.g. RTP. This will allow you to detect losses 
in the stream on the system layer (e.g. by discontinuity in sequence 
numbers). In such an environment you should also have timing associated 
with each picture which should guide you to proper output times. If 
there is no timing available, it might be beneficial to use the POC of 
the fields as an indicator.
Best regards,
Karsten
Jagannathan, Shyam wrote:
> Dear Experts,
> 
>  
> 
> What qualifies a pair of fields as complementary field pairs?
> 
>  
> 
> The standard says,
> 
>  
> 
> *3.1                 **complementary field pair: *A collective term for 
> a /complementary reference field pair/ or a /complementary non-reference 
> field pair/.
> 
> *3.2                 **complementary non-reference field pair*: Two 
> /non-reference fields/ that are in consecutive /access units/ in 
> /decoding order/ as two /coded fields/ of opposite parity where the 
> first /field /is not already a paired /field./
> 
> *3.3                 **complementary reference field pair*: Two 
> /reference fields/ that are in consecutive /access units/ in /decoding 
> order/ as two /coded fields /and share the same value of the frame_num 
> /syntax element/, where the second /field/ in /decoding order /is not an 
> /IDR picture/ and does not include a memory_management_control_operation 
> /syntax element /equal to 5/./
> 
>  
> 
>  
> 
> Let us assume a case where 2 non-reference field pairs appear in 
> decoding order as below,
> 
>  
> 
>     Frame num   :      7             7         
> 
> Decoding order  :| TF - BF - BF - TF |
> 
>  
> 
>  
> 
> If the BF picture access unit in the first pair is lost in a streaming 
> network (say),
> 
>  
> 
>     Frame num   :      7             7         
> 
> Decoding order  :| TF - X - BF - TF |
> 
>  
> 
>  
> 
>  the decoder will see TF belonging to first pair and BF belonging to 
> second pair and ‘pair’ them together as *complementary non-reference 
> field pair *as per standard definition.
> 
> This disturbs the correct decoding and hence display sequence.
> 
>  
> 
> Is my understanding correct?
> 
> How should a decoder behave in such cases?
> 
> Is there a sure shot way of finding complementary field pairs?
> 
>  
> 
> Thanks and Regards,
> 
> Shyam
> 
>  
> 
> 
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