From d77e75180d0fa28c243ce59aed93a47f378f6364 Mon Sep 17 00:00:00 2001
From: StephenGrable1 <stephengrable@gmail.com>
Date: Sat, 25 May 2024 15:21:47 -0400
Subject: [PATCH] add ffmpeg audio filter support enable -af flag pass through

Signed-off-by: Stephen Grable  <stephengrable@gmail.com>
---
 CHANGELOG.md                      |  1 +
 examples/ffmpeg_audio_filter.py   | 26 ++++++++++++++++++++++++++
 picamera2/outputs/ffmpegoutput.py |  5 ++++-
 3 files changed, 31 insertions(+), 1 deletion(-)
 create mode 100644 examples/ffmpeg_audio_filter.py

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 125730ac..2d8755e4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,7 @@
 ## Unreleased (on "next" branch)
 
 ### Added
+* FfmpegOutput support custom audio filter
 
 ### Changed
 
diff --git a/examples/ffmpeg_audio_filter.py b/examples/ffmpeg_audio_filter.py
new file mode 100644
index 00000000..e1106915
--- /dev/null
+++ b/examples/ffmpeg_audio_filter.py
@@ -0,0 +1,26 @@
+#!/usr/bin/python3
+import time
+
+from picamera2 import Picamera2
+from picamera2.encoders import H264Encoder
+from picamera2.outputs import FfmpegOutput
+
+picam2 = Picamera2()
+video_config = picam2.create_video_configuration()
+picam2.configure(video_config)
+encoder = H264Encoder(10000000)
+
+# audio filter takes the left channel and copies it to the right channel
+# below example copies c0 (left channel) to c1 (right channel) - convert mono to stereo
+
+# or add audio delay on left channel like this: audio_filter="pan=stereo|adelay=1500|0"
+# source for more examples: https://ffmpeg.org/ffmpeg-filters.html#Examples-2
+output = FfmpegOutput(
+    'ffmpeg_audio_filter_test.mp4',
+    audio=True,
+    audio_filter="pan=stereo|c0=c0|c1=c0"
+)
+
+picam2.start_recording(encoder, output)
+time.sleep(10)
+picam2.stop_recording()
diff --git a/picamera2/outputs/ffmpegoutput.py b/picamera2/outputs/ffmpegoutput.py
index ac431530..1f35c763 100644
--- a/picamera2/outputs/ffmpegoutput.py
+++ b/picamera2/outputs/ffmpegoutput.py
@@ -34,12 +34,13 @@ class FfmpegOutput(Output):
     """
 
     def __init__(self, output_filename, audio=False, audio_device="default", audio_sync=-0.3,
-                 audio_samplerate=48000, audio_codec="aac", audio_bitrate=128000, pts=None):
+                 audio_samplerate=48000, audio_codec="aac", audio_bitrate=128000, audio_filter=None, pts=None):
         super().__init__(pts=pts)
         self.ffmpeg = None
         self.output_filename = output_filename
         self.audio = audio
         self.audio_device = audio_device
+        self.audio_filter = audio_filter
         self.audio_sync = audio_sync
         self.audio_samplerate = audio_samplerate
         self.audio_codec = audio_codec
@@ -72,6 +73,8 @@ def start(self):
                            '-i', self.audio_device]
             audio_codec = ['-b:a', str(self.audio_bitrate),
                            '-c:a', self.audio_codec]
+            if self.audio_filter:  # Check if audio_filter is not empty or None
+                audio_codec.extend(['-af', self.audio_filter])
 
         command = ['ffmpeg'] + general_options + audio_input + video_input + \
             audio_codec + video_codec + self.output_filename.split()