From 7730205a0c20a17508de9f1d3c2d54a1e1827453 Mon Sep 17 00:00:00 2001
From: Ahmet Sait <git@ahmetsait.com>
Date: Tue, 19 Nov 2024 17:46:01 +0300
Subject: [PATCH] Implement `--lower-only`

---
 ffmpeg_normalize/__main__.py          | 15 +++++++++++++
 ffmpeg_normalize/_ffmpeg_normalize.py |  3 +++
 ffmpeg_normalize/_media_file.py       | 31 ++++++++++++++++++++++++---
 3 files changed, 46 insertions(+), 3 deletions(-)

diff --git a/ffmpeg_normalize/__main__.py b/ffmpeg_normalize/__main__.py
index 159fdde..d747064 100644
--- a/ffmpeg_normalize/__main__.py
+++ b/ffmpeg_normalize/__main__.py
@@ -235,6 +235,20 @@ def create_parser() -> argparse.ArgumentParser:
         default=0.0,
     )
 
+    group_ebu.add_argument(
+        "--lower-only",
+        action="store_true",
+        help=textwrap.dedent(
+            """\
+        Whether the audio should not increase in loudness.
+
+        If the measured loudness from the first pass is lower than the target
+        loudness then normalization pass will be skipped for the measured audio
+        source.
+        """
+        ),
+    )
+
     group_ebu.add_argument(
         "--dual-mono",
         action="store_true",
@@ -514,6 +528,7 @@ def _split_options(opts: str) -> list[str]:
         keep_lra_above_loudness_range_target=cli_args.keep_lra_above_loudness_range_target,
         true_peak=cli_args.true_peak,
         offset=cli_args.offset,
+        lower_only=cli_args.lower_only,
         dual_mono=cli_args.dual_mono,
         dynamic=cli_args.dynamic,
         audio_codec=cli_args.audio_codec,
diff --git a/ffmpeg_normalize/_ffmpeg_normalize.py b/ffmpeg_normalize/_ffmpeg_normalize.py
index 044acd6..67ae5f8 100644
--- a/ffmpeg_normalize/_ffmpeg_normalize.py
+++ b/ffmpeg_normalize/_ffmpeg_normalize.py
@@ -60,6 +60,7 @@ class FFmpegNormalize:
         keep_lra_above_loudness_range_target (bool, optional): Keep input loudness range above loudness range target. Defaults to False.
         true_peak (float, optional): True peak. Defaults to -2.0.
         offset (float, optional): Offset. Defaults to 0.0.
+        lower_only (bool, optional): Whether the audio should not increase in loudness. Defaults to False.
         dual_mono (bool, optional): Dual mono. Defaults to False.
         dynamic (bool, optional): Dynamic. Defaults to False.
         audio_codec (str, optional): Audio codec. Defaults to "pcm_s16le".
@@ -96,6 +97,7 @@ def __init__(
         keep_lra_above_loudness_range_target: bool = False,
         true_peak: float = -2.0,
         offset: float = 0.0,
+        lower_only: bool = False,
         dual_mono: bool = False,
         dynamic: bool = False,
         audio_codec: str = "pcm_s16le",
@@ -166,6 +168,7 @@ def __init__(
 
         self.true_peak = check_range(true_peak, -9, 0, name="true_peak")
         self.offset = check_range(offset, -99, 99, name="offset")
+        self.lower_only = lower_only
 
         # Ensure library user is passing correct types
         assert isinstance(dual_mono, bool), "dual_mono must be bool"
diff --git a/ffmpeg_normalize/_media_file.py b/ffmpeg_normalize/_media_file.py
index e844ddb..5e3ddf7 100644
--- a/ffmpeg_normalize/_media_file.py
+++ b/ffmpeg_normalize/_media_file.py
@@ -251,10 +251,35 @@ def _get_audio_filter_cmd(self) -> tuple[str, list[str]]:
         output_labels = []
 
         for audio_stream in self.streams["audio"].values():
-            if self.ffmpeg_normalize.normalization_type == "ebu":
-                normalization_filter = audio_stream.get_second_pass_opts_ebu()
+            skip_normalization = False
+            if self.ffmpeg_normalize.lower_only:
+                if self.ffmpeg_normalize.normalization_type == "ebu":
+                    if (
+                        audio_stream.loudness_statistics["ebu_pass1"] is not None and
+                        audio_stream.loudness_statistics["ebu_pass1"]["input_i"] < self.ffmpeg_normalize.target_level
+                    ):
+                        skip_normalization = True
+                elif self.ffmpeg_normalize.normalization_type == "peak":
+                    if (
+                        audio_stream.loudness_statistics["max"] is not None and
+                        audio_stream.loudness_statistics["max"] < self.ffmpeg_normalize.target_level
+                    ):
+                        skip_normalization = True
+                elif self.ffmpeg_normalize.normalization_type == "rms":
+                    if (
+                        audio_stream.loudness_statistics["mean"] is not None and
+                        audio_stream.loudness_statistics["mean"] < self.ffmpeg_normalize.target_level
+                    ):
+                        skip_normalization = True
+
+            if skip_normalization:
+                _logger.info(f"Stream {audio_stream.stream_id} had measured input loudness lower than target, skipping normalization.")
+                normalization_filter = "acopy"
             else:
-                normalization_filter = audio_stream.get_second_pass_opts_peakrms()
+                if self.ffmpeg_normalize.normalization_type == "ebu":
+                    normalization_filter = audio_stream.get_second_pass_opts_ebu()
+                else:
+                    normalization_filter = audio_stream.get_second_pass_opts_peakrms()
 
             input_label = f"[0:{audio_stream.stream_id}]"
             output_label = f"[norm{audio_stream.stream_id}]"