同步、背压、延迟与质量评估：练习答案

参考实现

独立运行：

def latest_by_media_time(frames):
    return max(frames,key=lambda x:x['pts']) if frames else None
assert latest_by_media_time([{'pts':99},{'pts':33},{'pts':66}]) == {'pts':99}
assert latest_by_media_time([]) is None

还应拒绝其他会话的帧，并明确是否允许未来时间戳；PTS只有在同一时钟基准下可比较。

返回题目。

质量与恢复

独立保存 answer_quality.py，Python3.11+运行；正文完整SQLite重开实验直接保留，再添加以下时延变体。

import sqlite3,tempfile
from pathlib import Path

def edits(a,b):
    row=list(range(len(b)+1))
    for i,x in enumerate(a,1):
        new=[i]
        for j,y in enumerate(b,1):
            new.append(min(new[-1]+1,row[j]+1,row[j-1]+(x!=y)))
        row=new
    return row[-1]
reference='book room for June six'.split()
hypothesis='book room for June seven'.split()
assert edits(reference,hypothesis)/len(reference)==.2
# 大部分文字正确仍可订错日期，任务断言是独立门槛。
assert hypothesis[-1]!='six'
assert edits(['yes'],['no','no','no'])/1==3

trace={'speech_end':1.,'vad_end':1.2,'first_audio':1.6,'play_start':1.8,
       'interruption':2.,'last_old_sample':2.04}
assert abs(trace['play_start']-trace['speech_end']-.8)<1e-9
assert abs(trace['last_old_sample']-trace['interruption']-.04)<1e-9
# 真实SQLite重开：新连接不能把同一业务意图当作新动作。
with tempfile.TemporaryDirectory() as directory:
    path=Path(directory)/'operations.db'
    def open_db():
        db=sqlite3.connect(path)
        db.execute('CREATE TABLE IF NOT EXISTS operation (business_id TEXT PRIMARY KEY, argument TEXT, result TEXT)')
        return db
    def apply(db,business_id,argument):
        with db:
            db.execute('INSERT OR IGNORE INTO operation VALUES (?,?,?)',(business_id,argument,'confirmed:'+argument))
            old=db.execute('SELECT argument,result FROM operation WHERE business_id=?',(business_id,)).fetchone()
            if old[0]!=argument:raise ValueError('conflicting replay')
            return old[1]
    db=open_db();first=apply(db,'intent1','June six');db.close()
    db=open_db();assert apply(db,'intent1','June six')==first
    try:apply(db,'intent1','June seven')
    except ValueError:pass
    else:raise AssertionError('changed intent reused old confirmation')
    assert db.execute('SELECT COUNT(*) FROM operation').fetchone()[0]==1
    db.close()
print('word errors, heard latency and durable operation identity passed')

model_delay=trace['first_audio']-trace['speech_end']
trace['play_start']+=.4
assert abs(trace['play_start']-trace['speech_end']-1.2)<1e-9
assert abs(trace['first_audio']-trace['speech_end']-model_delay)<1e-9
print('playback delay isolated from model delay')

一次替换和两次插入使yes→no no no的编辑距离为3，除以一个参考词得到3。不同日期重放在同一业务键下必须失败，原账本记录保持不变。