diff --git a/fffw/graph/base.py b/fffw/graph/base.py
index e3e9d8b..45dac19 100644
--- a/fffw/graph/base.py
+++ b/fffw/graph/base.py
@@ -59,7 +59,14 @@ class Dest(Traversable):
 
     @property
     def meta(self) -> Optional[Meta]:
-        return self.get_meta_data(self)
+        metadata = self.get_meta_data(self)
+        if metadata is None:
+            return None
+        return self.transform(metadata)
+
+    def transform(self, *metadata: Meta) -> Meta:
+        """ Apply codec changes to stream metadata."""
+        return metadata[0]
 
     @property
     def edge(self) -> Optional["Edge"]:

diff --git a/tests/test_graph.py b/tests/test_graph.py
index b85e73b..ecf7948 100644
--- a/tests/test_graph.py
+++ b/tests/test_graph.py
@@ -1,4 +1,4 @@
-from dataclasses import dataclass
+from dataclasses import dataclass, replace
 from typing import cast
 from unittest import TestCase
 
@@ -6,6 +6,7 @@ from fffw.encoding import inputs, outputs, codecs
 from fffw.encoding.complex import FilterComplex
 from fffw.encoding.filters import *
 from fffw.graph import *
+from fffw.wrapper import param
 
 
 @dataclass
@@ -24,6 +25,15 @@ class ScaleCuda(Scale):
     hardware = 'cuda'
 
 
+@dataclass
+class FdkAAC(codecs.AudioCodec):
+    codec = 'libfdk_aac'
+    bitrate: int = param(name='b', stream_suffix=True)
+
+    def transform(self, metadata: Meta) -> Meta:
+        return replace(metadata, bitrate=self.bitrate)
+
+
 class FilterGraphTestCase(TestCase):
 
     def setUp(self) -> None:
@@ -37,10 +47,18 @@ class FilterGraphTestCase(TestCase):
             frame_rate=10.0,
             frame_count=3000
         )
+        self.source_audio_duration = 200.0
+        self.source_sampling_rate = 48000
+        self.source_samples_count = (self.source_audio_duration *
+                                     self.source_sampling_rate)
+        self.source_audio_bitrate = 128000
         self.audio_metadata = audio_meta_data(
-            duration=200.0,
-            sampling_rate=48000,
-            samples_count=200 * 48000)
+            duration=self.source_audio_duration,
+            sampling_rate=self.source_sampling_rate,
+            samples_count=self.source_samples_count,
+            bit_rate=self.source_audio_bitrate,
+        )
+        self.target_audio_bitrate = 64000
 
         self.source = inputs.Input(
             input_file='input.mp4',
@@ -49,7 +67,7 @@ class FilterGraphTestCase(TestCase):
         self.output = outputs.output_file(
             'output.mp4',
             codecs.VideoCodec('libx264'),
-            codecs.AudioCodec('libfdk_aac'))
+            FdkAAC(bitrate=self.target_audio_bitrate))
         self.input_list = inputs.InputList((self.source,))
         self.output_list = outputs.OutputList((self.output,))
         self.fc = FilterComplex(self.input_list, self.output_list)
@@ -361,3 +379,26 @@ class FilterGraphTestCase(TestCase):
             s | Upload(device=cuda) | UniversalFilter()
         except ValueError:  # pragma: no cover
             self.fail("hardware validation unexpectedly failed")
+
+    def test_codec_metadata_transform(self):
+        """
+        Codecs parameters applied to stream metadata when using transform.
+        """
+        with self.subTest('codec with transform'):
+            self.source.audio > self.output
+            am = cast(AudioMeta, self.output.codecs[1].meta)
+            self.assertEqual(am.bitrate, self.target_audio_bitrate)
+
+        with self.subTest('no input metadata'):
+            no_meta_input = inputs.input_file('input.mp4')
+            output = outputs.output_file('output.mp4',
+                                         codecs.AudioCodec('aac'))
+            no_meta_input.audio > output.audio
+            self.assertIsNone(output.codecs[0].meta)
+
+        with self.subTest('no transform'):
+            output = outputs.output_file('output.mp4',
+                                         codecs.AudioCodec('aac'))
+            self.source.audio > output.audio
+            am = cast(AudioMeta, output.codecs[0].meta)
+            self.assertEqual(am.bitrate, self.audio_metadata.bitrate)
diff --git a/tests/test_vector.py b/tests/test_vector.py
index bc4e8c8..3f74cf0 100644
--- a/tests/test_vector.py
+++ b/tests/test_vector.py
@@ -9,6 +9,15 @@ from tests.base import BaseTestCase
 from tests.test_ffmpeg import Volume
 
 
+@dataclass
+class AAC(AudioCodec):
+    codec = 'aac'
+    bitrate: int = param(name='b', stream_suffix=True)
+
+    def transform(self, metadata: Meta) -> Meta:
+        return replace(metadata, bitrate=self.bitrate)
+
+
 @dataclass
 class StubFilter(AudioFilter):
     filter = 'stub'
@@ -30,13 +39,14 @@ class VectorTestCase(BaseTestCase):
     def setUp(self) -> None:
         super().setUp()
         self.video_meta = video_meta_data(width=1920, height=1080)
-        self.audio_meta = audio_meta_data()
+        self.audio_meta = audio_meta_data(bit_rate=128000)
+        self.audio_bitrate = 64000
         self.source = input_file('input.mp4',
                                  Stream(VIDEO, self.video_meta),
                                  Stream(AUDIO, self.audio_meta))
         self.output1 = output_file('output1.mp4',
                                    VideoCodec('libx264'),
-                                   AudioCodec('aac'))
+                                   AAC(bitrate=self.audio_bitrate))
         self.output2 = output_file('output2.mp5',
                                    VideoCodec('libx265'),
                                    AudioCodec('libfdk_aac'))
@@ -63,7 +73,9 @@ class VectorTestCase(BaseTestCase):
         """
         with self.subTest("input meta"):
             v = self.simd.video
+            a = self.simd.audio
             self.assertEqual(v.meta, self.video_meta)
+            self.assertEqual(a.meta, self.audio_meta)
 
         with self.subTest("filter meta"):
             v = v | Scale(1280, 720)
@@ -71,9 +83,10 @@ class VectorTestCase(BaseTestCase):
             self.assertEqual(v.meta, expected)
 
         with self.subTest("codec meta"):
+            expected = replace(self.audio_meta, bitrate=self.audio_bitrate)
             simd = SIMD(self.source, self.output1)
-            x = v > simd
-            self.assertEqual(x.meta, expected)
+            a = a > simd
+            self.assertEqual(a.meta, expected)
 
     def test_vector_metadata_for_multiple_streams(self):
         """
@@ -88,7 +101,7 @@ class VectorTestCase(BaseTestCase):
         self.assert_simd_args(
             '-i', 'input.mp4',
             '-map', '0:v', '-c:v', 'libx264',
-            '-map', '0:a', '-c:a', 'aac',
+            '-map', '0:a', '-c:a', 'aac', '-b:a', '64000',
             'output1.mp4',
             '-map', '0:v', '-c:v', 'libx265',
             '-map', '0:a', '-c:a', 'libfdk_aac',
@@ -105,7 +118,7 @@ class VectorTestCase(BaseTestCase):
             '[0:a]volume=30.00[a:volume0];'
             '[a:volume0]asplit[aout0][aout1]',
             '-map', '0:v', '-c:v', 'libx264',
-            '-map', '[aout0]', '-c:a', 'aac',
+            '-map', '[aout0]', '-c:a', 'aac', '-b:a', '64000',
             'output1.mp4',
             '-map', '0:v', '-c:v', 'libx265',
             '-map', '[aout1]', '-c:a', 'libfdk_aac',
@@ -122,7 +135,7 @@ class VectorTestCase(BaseTestCase):
             '[0:a]asplit[a:asplit0][aout0];'
             '[a:asplit0]volume=30.00[aout1]',
             '-map', '0:v', '-c:v', 'libx264',
-            '-map', '[aout0]', '-c:a', 'aac',
+            '-map', '[aout0]', '-c:a', 'aac', '-b:a', '64000',
             'output1.mp4',
             '-map', '0:v', '-c:v', 'libx265',
             '-map', '[aout1]', '-c:a', 'libfdk_aac',
@@ -137,7 +150,7 @@ class VectorTestCase(BaseTestCase):
             '-filter_complex',
             '[0:a]asplit[aout0][aout1]',
             '-map', '0:v', '-c:v', 'libx264',
-            '-map', '[aout0]', '-c:a', 'aac',
+            '-map', '[aout0]', '-c:a', 'aac', '-b:a', '64000',
             'output1.mp4',
             '-map', '0:v', '-c:v', 'libx265',
             '-map', '[aout1]', '-c:a', 'libfdk_aac',
@@ -154,7 +167,7 @@ class VectorTestCase(BaseTestCase):
             '[a:asplit0]volume=20.00[aout0];'
             '[a:asplit1]volume=30.00[aout1]',
             '-map', '0:v', '-c:v', 'libx264',
-            '-map', '[aout0]', '-c:a', 'aac',
+            '-map', '[aout0]', '-c:a', 'aac', '-b:a', '64000',
             'output1.mp4',
             '-map', '0:v', '-c:v', 'libx265',
             '-map', '[aout1]', '-c:a', 'libfdk_aac',
@@ -170,7 +183,7 @@ class VectorTestCase(BaseTestCase):
             '[0:a]volume=30.00[a:volume0];'
             '[a:volume0]asplit[aout0][aout1]',
             '-map', '0:v', '-c:v', 'libx264',
-            '-map', '[aout0]', '-c:a', 'aac',
+            '-map', '[aout0]', '-c:a', 'aac', '-b:a', '64000',
             'output1.mp4',
             '-map', '0:v', '-c:v', 'libx265',
             '-map', '[aout1]', '-c:a', 'libfdk_aac',
@@ -193,7 +206,7 @@ class VectorTestCase(BaseTestCase):
             '[a:asplit1]volume=30.00[a:volume1];'
             '[a:volume1]stub[aout1]',
             '-map', '0:v', '-c:v', 'libx264',
-            '-map', '[aout0]', '-c:a', 'aac',
+            '-map', '[aout0]', '-c:a', 'aac', '-b:a', '64000',
             'output1.mp4',
             '-map', '0:v', '-c:v', 'libx265',
             '-map', '[aout1]', '-c:a', 'libfdk_aac',
@@ -227,7 +240,7 @@ class VectorTestCase(BaseTestCase):
             '[v:split4][v:scale0]overlay[vout0];'
             '[v:split5][v:scale1]overlay[vout1]',
             '-map', '[vout0]', '-c:v', 'libx264',
-            '-map', '0:a', '-c:a', 'aac',
+            '-map', '0:a', '-c:a', 'aac', '-b:a', '64000',
             'output1.mp4',
             '-map', '[vout1]', '-c:v', 'libx265',
             '-map', '0:a', '-c:a', 'libfdk_aac',
@@ -255,7 +268,7 @@ class VectorTestCase(BaseTestCase):
             '[v:split2][v:scale0]overlay[vout0];'
             '[v:split3][v:scale1]overlay[vout1]',
             '-map', '[vout0]', '-c:v', 'libx264',
-            '-map', '0:a', '-c:a', 'aac',
+            '-map', '0:a', '-c:a', 'aac', '-b:a', '64000',
             'output1.mp4',
             '-map', '[vout1]', '-c:v', 'libx265',
             '-map', '0:a', '-c:a', 'libfdk_aac',
@@ -279,7 +292,7 @@ class VectorTestCase(BaseTestCase):
             '[0:v]split[v:split0][vout0];'
             '[1:v][v:split0]overlay[vout1]',
             '-map', '[vout1]', '-c:v', 'libx264',
-            '-map', '0:a', '-c:a', 'aac',
+            '-map', '0:a', '-c:a', 'aac', '-b:a', '64000',
             'output1.mp4',
             '-map', '[vout0]', '-c:v', 'libx265',
             '-map', '0:a', '-c:a', 'libfdk_aac',
@@ -310,7 +323,7 @@ class VectorTestCase(BaseTestCase):
             '[1:v][v:split0]concat[vout1];'
             '[1:a][a:asplit0]concat=v=0:a=1:n=2[aout1]',
             '-map', '[vout1]', '-c:v', 'libx264',
-            '-map', '[aout1]', '-c:a', 'aac',
+            '-map', '[aout1]', '-c:a', 'aac', '-b:a', '64000',
             'output1.mp4',
             '-map', '[vout0]', '-c:v', 'libx265',
             '-map', '[aout0]', '-c:a', 'libfdk_aac',
@@ -333,7 +346,7 @@ class VectorTestCase(BaseTestCase):
             '[1:v]scale=w=120:h=120[v:scale0];'
             '[0:v][v:scale0]overlay[v:overlay0]',
             '-map', '[vout0]', '-c:v', 'libx264',
-            '-map', '0:a', '-c:a', 'aac',
+            '-map', '0:a', '-c:a', 'aac', '-b:a', '64000',
             'output1.mp4',
             '-map', '[vout1]', '-c:v', 'libx265',
             '-map', '0:a', '-c:a', 'libfdk_aac',
@@ -365,7 +378,7 @@ class VectorTestCase(BaseTestCase):
             '-map', '[vout0]',
             '-c:v', 'libx264',
             '-map', '[aout0]',
-            '-c:a', 'aac',
+            '-c:a', 'aac', '-b:a', '64000',
             'output1.mp4',
             '-map', '[vout1]',
             '-c:v', 'libx265',

Codecs should transform meta
I.e. AudioCodec: when changing sampling rate, it should also change samples count.
For VideoCodec frame rate could be changed and frames count (#66) will also change.
tests/test_graph.py::FilterGraphTestCase::test_codec_metadata_transform tests/test_vector.py::VectorTestCase::test_vector_metadata
tests/test_graph.py::FilterGraphTestCase::test_any_hardware_filter tests/test_graph.py::FilterGraphTestCase::test_audio_trim_metadata tests/test_graph.py::FilterGraphTestCase::test_concat_audio_metadata tests/test_graph.py::FilterGraphTestCase::test_concat_video_metadata tests/test_graph.py::FilterGraphTestCase::test_disabled_filters tests/test_graph.py::FilterGraphTestCase::test_ensure_audio tests/test_graph.py::FilterGraphTestCase::test_ensure_video tests/test_graph.py::FilterGraphTestCase::test_filter_graph tests/test_graph.py::FilterGraphTestCase::test_filter_validates_hardware_device tests/test_graph.py::FilterGraphTestCase::test_filter_validates_stream_kind tests/test_graph.py::FilterGraphTestCase::test_overlay_metadata tests/test_graph.py::FilterGraphTestCase::test_scale_changes_metadata tests/test_graph.py::FilterGraphTestCase::test_setpts_metadata tests/test_graph.py::FilterGraphTestCase::test_skip_not_connected_sources tests/test_graph.py::FilterGraphTestCase::test_video_trim_metadata tests/test_vector.py::VectorTestCase::test_apply_filter_with_equal_params tests/test_vector.py::VectorTestCase::test_apply_filter_with_params_vector tests/test_vector.py::VectorTestCase::test_clone_filter_with_skipped_params tests/test_vector.py::VectorTestCase::test_clone_inputs_for_destination_filter tests/test_vector.py::VectorTestCase::test_clone_streams tests/test_vector.py::VectorTestCase::test_connect_filter_to_a_vector tests/test_vector.py::VectorTestCase::test_connect_stream_to_simd tests/test_vector.py::VectorTestCase::test_multiple_disabled_filters tests/test_vector.py::VectorTestCase::test_no_filter_graph tests/test_vector.py::VectorTestCase::test_overlay_with_mask tests/test_vector.py::VectorTestCase::test_preroll_with_mask tests/test_vector.py::VectorTestCase::test_same_filter_for_all_streams tests/test_vector.py::VectorTestCase::test_same_filter_with_mask tests/test_vector.py::VectorTestCase::test_split_filter_if_vector_differs tests/test_vector.py::VectorTestCase::test_vector_kind tests/test_vector.py::VectorTestCase::test_vector_metadata_for_multiple_streams