fix(subtitle): preserve more VAD context by default

Signed-off-by: zhifu gao <[email protected]>

examples/subtitle/README.md

@@ -22,6 +22,9 @@ python generate_subtitle.py audio.wav --device cpu
 
 # Preserve raw model sentence boundaries
 python generate_subtitle.py audio.wav --segment-mode sentence
+
+# Use shorter VAD segments when memory is limited
+python generate_subtitle.py audio.wav --max-single-segment-time 30000
 ```
 
 ## Output Example (SRT)
@@ -44,6 +47,7 @@ python generate_subtitle.py audio.wav --segment-mode sentence
 | `--segment-mode` | readable | Cue grouping: readable or raw sentence boundaries |
 | `--model` | SenseVoiceSmall | ASR model |
 | `--device` | cuda | Device: cuda or cpu |
+| `--max-single-segment-time` | 60000 | Maximum VAD segment length in milliseconds; reduce it when memory is limited |
 | `--spk` | off | Add speaker labels |
 | `--lang` | auto | Language hint |
 | `-o` | input.srt | Output path |
@@ -52,6 +56,10 @@ Readable mode joins only adjacent short or continuation cues within bounded
 gap, duration, length, and speaker limits. It does not rewrite recognized text
 or punctuation.
 
+The default 60-second VAD limit gives subtitle generation more context at
+speech boundaries. For memory-constrained machines, lower it explicitly (for
+example, `--max-single-segment-time 30000`).
+
 ## Install
 
 ```bash

examples/subtitle/generate_subtitle.py

@@ -73,6 +73,13 @@ def main():
     )
     parser.add_argument("--model", default="iic/SenseVoiceSmall")
     parser.add_argument("--device", default="cuda")
+    parser.add_argument(
+        "--max-single-segment-time",
+        type=int,
+        default=60000,
+        metavar="MS",
+        help="Maximum VAD segment length in milliseconds (default: 60000)",
+    )
     parser.add_argument("--spk", action="store_true", help="Include speaker labels")
     parser.add_argument("--lang", default="auto")
     args = parser.parse_args()
@@ -88,7 +95,7 @@ def main():
     from funasr import AutoModel
 
     kwargs = {"model": args.model, "vad_model": "fsmn-vad", "punc_model": "ct-punc",
-              "vad_kwargs": {"max_single_segment_time": 30000},
+              "vad_kwargs": {"max_single_segment_time": args.max_single_segment_time},
               "device": args.device, "disable_update": True}
     if args.spk:
         kwargs["spk_model"] = "cam++"

tests/test_generate_subtitle.py

@@ -68,6 +68,7 @@ def test_generate_subtitle_requests_sentence_timestamps_and_writes_segmented_srt
     module.main()
 
     assert captured["model_kwargs"]["punc_model"] == "ct-punc"
+    assert captured["model_kwargs"]["vad_kwargs"] == {"max_single_segment_time": 60000}
     assert captured["generate_kwargs"]["language"] == "zh"
     assert captured["generate_kwargs"]["sentence_timestamp"] is True
     assert captured["generate_kwargs"]["output_timestamp"] is True