Abstract: Block Flow Matching combines block-level autoregression with intra-block parallelism for efficient and high-quality Text-to-Speech (TTS). However, using a fixed block size during inference ignores the non-uniform modeling difficulty of speech, which can cause unstable velocity estimation in challenging regions. This motivates the need for a reliability metric that can guide dynamic adjustment of block size. We propose Trajectory Confidence (TC), a geometric measure derived from trajectory straightness during ODE integration, and introduce TC-Guided Dynamic Block Inference (TC-DBI), a plug-and-play strategy that truncates and regenerates unreliable regions to adapt block size without architectural changes. Experiments show that TC correlates strongly with generation errors, and TC-DBI improves robustness and perceptual quality while maintaining comparable efficiency.

Model Architecture

Main Results

We conducted our evaluations on the seed-test-zh and seed-test-en benchmarks from Seed-TTS. Since no publicly available BFM model matches our training scale, we reproduced a Block Flow Matching model (BFM) as a baseline. For a comprehensive comparison, we also include CosyVoice2, MaskGCT, and F5-TTS, covering AR and NAR paradigms.

文本 (Transcript)	CosyVoice2	F5-TTS	MaskGCT	BFM (ours)	BFM with TC-DBI (ours)
中文 (Chinese)
一个挪动一步，另一个也挪一步，可都是斜着步子兜圈子。
小丁要根据现有微信截图，要回奖金的概率。
关键是气质女神啊，一开始先买一部新车。
你要什么有什么，那里有正装也有休闲的衣服。
窗帘几乎全烧光了，挂窗帘的棍被烧得通红，四边全是火焰。
英文 (English)
It is operated by the New York City Department of Parks and Recreation.
While at Cambridge he also gained experience in using the telegraph.
Next was "The Last King of Scotland", which won an Oscar for best actor.
Dense clouds of smoke or dust can be seen through a powerful telescope.
The bridge is located just west of Commodore Park.

Ablation Study: Impact of Confidence Threshold τ

To further examine how trajectory confidence translates into inference gains, we evaluate TC-DBI under different thresholds τ.

文本 (Transcript)	Fixed Block Size	τ = 0.65	τ = 0.70	τ = 0.75	τ = 0.80
中文 (Chinese)
身穿绿衣裳，肚里水汪汪，生的儿子儿多，个个黑脸膛。
当我们做体验时，我们到底在做什么。
如果您不愿意开刀的话，那就只能使用缓慢排水法。
这薄壳被外面的水泡软，被雪和泥土温暖，被阳光射透。
小黑狗摆摆尾巴说，我身上没有汗腺，可舌头上有许多汗腺的呢。
英文 (English)
For the full history, see List of Southern Conference men's basketball champions.
There is also a genetic test that can be done for this disorder.
He last served as a member of parliament from the opposition.
In May of the same year he was made Chaplain to the King.
‘Coming, Sir,’ replied Sam, running upstairs.