diff --git a/handlers/render_video.py b/handlers/render_video.py
index 25f176c..9b2f2a6 100644
--- a/handlers/render_video.py
+++ b/handlers/render_video.py
@@ -725,8 +725,11 @@ class RenderSegmentTsHandler(BaseHandler):
                 break
 
         combined_pts_factor = (1.0 / speed) * ospeed_factor
+        # 统一归零视频起始时间戳，避免源素材非 0 起始 PTS 造成封装后首帧冻结
         if combined_pts_factor != 1.0:
-            filters.append(f"setpts={combined_pts_factor}*PTS")
+            filters.append(f"setpts={combined_pts_factor}*(PTS-STARTPTS)")
+        else:
+            filters.append("setpts=PTS-STARTPTS")
 
         # 2. LUT 调色
         if lut_file:
diff --git a/tests/unit/test_render_video_effects.py b/tests/unit/test_render_video_effects.py
index 0a2aa1d..a8498f5 100644
--- a/tests/unit/test_render_video_effects.py
+++ b/tests/unit/test_render_video_effects.py
@@ -137,7 +137,22 @@ def test_ospeed_does_not_trigger_filter_complex(tmp_path):
     # 验证 setpts 滤镜
     vf_idx = command.index('-vf')
     vf_value = command[vf_idx + 1]
-    assert 'setpts=2.0*PTS' in vf_value
+    assert 'setpts=2.0*(PTS-STARTPTS)' in vf_value
+
+
+def test_default_speed_always_normalizes_pts(tmp_path):
+    handler = _create_handler(tmp_path)
+    render_spec = RenderSpec()
+    output_spec = OutputSpec(width=1080, height=1920, fps=30)
+
+    filters = handler._build_video_filters(
+        render_spec=render_spec,
+        output_spec=output_spec,
+        duration_ms=6000,
+        source_duration_sec=10.0,
+    )
+
+    assert 'setpts=PTS-STARTPTS' in filters
 
 
 def test_ospeed_combined_with_speed(tmp_path):
@@ -153,7 +168,7 @@ def test_ospeed_combined_with_speed(tmp_path):
         source_duration_sec=10.0,
     )
 
-    assert 'setpts=1.5*PTS' in filters
+    assert 'setpts=1.5*(PTS-STARTPTS)' in filters
 
 
 def test_ospeed_with_complex_effects(tmp_path):
@@ -171,7 +186,7 @@ def test_ospeed_with_complex_effects(tmp_path):
     # zoom 触发 filter_complex
     assert '[v_base]' in filters
     # setpts 在 base_chain 中
-    assert 'setpts=2.0*PTS' in filters
+    assert 'setpts=2.0*(PTS-STARTPTS)' in filters
     # zoom 正常处理
     assert "overlay=0:0:enable='between(t,1.0,3.0)'" in filters
 
@@ -188,8 +203,8 @@ def test_only_first_ospeed_is_used(tmp_path):
         source_duration_sec=10.0,
     )
 
-    assert 'setpts=2.0*PTS' in filters
-    assert 'setpts=5.0*PTS' not in filters
+    assert 'setpts=2.0*(PTS-STARTPTS)' in filters
+    assert 'setpts=5.0*(PTS-STARTPTS)' not in filters
 
 
 def test_ospeed_affects_tpad_calculation(tmp_path):
diff --git a/tests/unit/test_video_encode_args.py b/tests/unit/test_video_encode_args.py
new file mode 100644
index 0000000..527d355
--- /dev/null
+++ b/tests/unit/test_video_encode_args.py
@@ -0,0 +1,25 @@
+# -*- coding: utf-8 -*-
+
+from constant import HW_ACCEL_CUDA, HW_ACCEL_NONE, HW_ACCEL_QSV
+from handlers.base import get_video_encode_args
+
+
+def _assert_bframe_disabled(args):
+    assert '-bf' in args
+    bf_index = args.index('-bf')
+    assert args[bf_index + 1] == '0'
+
+
+def test_get_video_encode_args_disable_b_frames_for_software():
+    args = get_video_encode_args(HW_ACCEL_NONE)
+    _assert_bframe_disabled(args)
+
+
+def test_get_video_encode_args_disable_b_frames_for_qsv():
+    args = get_video_encode_args(HW_ACCEL_QSV)
+    _assert_bframe_disabled(args)
+
+
+def test_get_video_encode_args_disable_b_frames_for_cuda():
+    args = get_video_encode_args(HW_ACCEL_CUDA)
+    _assert_bframe_disabled(args)