LL-HLS PART-HOLD-BACK tag doesnot take effect

Hi, Im trying to use ios15.0 client to play LL-HLS media stream. I provide a media playlist to the player but find it seems that PART-HOLD-BACK tag, mentioned in LL-HLS, failes to task effect. In other words, the player fails to follow PART-HOLD-BACK's behavior mentioned in LL-HLS documentation when playing the media. Anyone can help me check whether there needs some change to my media playlist? Or there is something stubborn in LL-HLS protocol itself, lol.

#EXT-X-TARGETDURATION:2
#EXT-X-VERSION:9
#EXT-X-SERVER-CONTROL:CAN-BLOCK-RELOAD=YES,PART-HOLD-BACK=0.640
#EXT-X-MAP:URI="audio_sample.m4i"
#EXT-X-PART-INF:PART-TARGET=0.213
#EXT-X-MEDIA-SEQUENCE:818343598
#EXT-X-PROGRAM-DATE-TIME:2021-11-12T03:19:56.330Z
#EXTINF:2.005,
audio_sample-147301847669700-PolicyMode_llhls9_2_cmaf-0.m4a?
#EXT-X-PROGRAM-DATE-TIME:2021-11-12T03:19:58.335Z
#EXTINF:2.005,
audio_sample-147301847850180-PolicyMode_llhls9_2_cmaf-0.m4a?
#EXT-X-PROGRAM-DATE-TIME:2021-11-12T03:20:00.340Z
#EXTINF:2.005,
audio_sample-147301848030660-PolicyMode_llhls9_2_cmaf-0.m4a?
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848211140-part_0.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848211140-part_1.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848211140-part_2.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848211140-part_3.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848211140-part_4.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848211140-part_5.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848211140-part_6.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848211140-part_7.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848211140-part_8.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.064,URI="audio_sample-147301848211140-part_9.m4a?",INDEPENDENT=YES
#EXT-X-PROGRAM-DATE-TIME:2021-11-12T03:20:02.346Z
#EXTINF:1.984,
audio_sample-147301848211140-PolicyMode_llhls9_2_cmaf-0.m4a?
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848389700-part_0.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848389700-part_1.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848389700-part_2.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848389700-part_3.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848389700-part_4.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848389700-part_5.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848389700-part_6.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848389700-part_7.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848389700-part_8.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.085,URI="audio_sample-147301848389700-part_9.m4a?",INDEPENDENT=YES
#EXT-X-PROGRAM-DATE-TIME:2021-11-12T03:20:04.330Z
#EXTINF:2.005,
audio_sample-147301848389700-PolicyMode_llhls9_2_cmaf-0.m4a?
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848570180-part_0.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848570180-part_1.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848570180-part_2.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848570180-part_3.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848570180-part_4.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848570180-part_5.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848570180-part_6.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848570180-part_7.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848570180-part_8.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.085,URI="audio_sample-147301848570180-part_9.m4a?",INDEPENDENT=YES
#EXT-X-PROGRAM-DATE-TIME:2021-11-12T03:20:06.335Z
#EXTINF:2.005,
audio_sample-147301848570180-PolicyMode_llhls9_2_cmaf-0.m4a?
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848750660-part_0.m4a?",INDEPENDENT=YES
#EXT-X-PART:DURATION=0.213,URI="audio_sample-147301848750660-part_1.m4a?",INDEPENDENT=YES
#EXT-X-PRELOAD-HINT:TYPE=PART,URI="audio_sample-147301848750660-part_2.m4a?"

hello

hello

LL-HLS PART-HOLD-BACK tag doesnot take effect
 
 
Q