GST clock running-time

• clock running-time

= absolute time - base time

 

 

• buffer running time

buffer timestamp 와 buffer에 앞선 SEGMETN event 필요 (valid timestamp range)

 

 

• live source

buffer를 얻은 running-time이 pipeline clock의 running-time과 정확히 일치해야 함

live source는 buffer에 ts를 넣음

 

 

• non-live source

buffer의 timestamp를 설정 (0부터 설정)

 

 

• demuxer

ts를 outging buffer에도 계산하여 ts 설정

 

 

QoS

• 버퍼가 늦게 도착 -> QoS에 문제
• 원인
  • CPU load, network 문제, 다른 I/O 등의 문제 등등

 

QoS event

• 문제 시 QOS event를 upstream으로 보내 datarate 조절에 사용
• upstream의 src pad의 event handler가 받음

 

QoS 측정

• 보통 running average로 proportion을 보고 처리
• 연속되는 두 buffer의 처리 시간으로 측정

 

단기 교정 = drop

• jitter > 0이면, 
  • negative jitter: early
  • positive jitter: late
• 현재 ts가 늦었으니, 이전것 모두 drop

 

장기 교정 = 성능 개선

• proportion을 보고
• frame drop
• 복잡도 감소
• low quality source사용
• CPU 할당 등의 처리를 수행

 

throttle mode

• 보통 sink에서 구현
• throttle interval에 설정된 jitter를 지닌 QoS event를 upstream에 전달
• upstream은 이를 보고 buffer를 skip할지 drop 할지 결정