What is PMT descriptor of H.264 encrypted streams in TS.

https://developer.apple.com/library/prerelease/ios/documentation/AudioVideo/Conceptual/HLS_Sample_Encryption/TransportStreamSignaling/TransportStreamSignaling.html#//apple_ref/doc/uid/TP40012862-CH3-SW1

As per the documentation from apple descriptor of of the sample-aes encrypted video stream should be 'zavc'

The

stream_type

0xdb

ES_info_length

private_data_indicator

'zavc'

but while parsing the encrypted sample we are getting

stream_type : 0xdb

and descriptor as "acvd"

This encrypted stream has been provided from apple and can we consider this video stream is not encrypted or the descriptor value is given wrong in specification.