update ffmpeg cheatsheet with trimming audio

content/ffmpeg-cheatsheet.rst

@@ -18,17 +18,17 @@ first and last 4 seconds of audio and video:
 .. code-block:: bash
 
   ffmpeg \
-    # start at minute 1
+    # start at minute 1 \
     -ss 00:01:00 \
-    # duration 20 seconds
+    # duration 20 seconds \
     -t 20 \
-    # input video
+    # input video \
     -i myinvideo.webm \
-    # audio fade
+    # audio fade \
     -af "afade=in:d=4,afade=t=out:st=16:d=4" \
-    # video fade
+    # video fade \
     -vf "fade=in:d=4,fade=out:st=16:d=4" \
-    # output video
+    # output video \
     myoutvideo.webm
 
 Normalize audio
@@ -38,9 +38,9 @@ Normalize audio
 
   ffmpeg \
     -i myinvideo.webm \
-    # integrated loudness (I) -16
-    # loudness range (LRA) 11
-    # max true peak (TP) -1.5
+    # integrated loudness (I) -16 \
+    # loudness range (LRA) 11 \
+    # max true peak (TP) -1.5 \
     -af loudnorm=I=-16:LRA=11:TP=-1.5 \
     myoutvideo.webm
 
@@ -55,10 +55,23 @@ file 1 and merge them into a new output file
 
   ffmpeg \
     -i myinvideo.webm \
-    # delay audio by 1.0 second
-    # negatives are also valid
+    # delay audio by 1.0 second \
+    # negatives are also valid \
     -itsoffset 1.0 \
     -i myinvideo.webm \
     -vcodec copy -acodec copy \
     -map 0:0 -map 1:1 \
     myoutvideo.webm
+
+Trim first n seconds from audio
+-------------------------------
+
+.. code-block:: bash
+
+  ffmpeg \
+    -i myinaudio.ogg \
+    # trim first 10 seconds \
+    -ss 10 \
+    # copy audio stream \
+    -acodec copy \
+    myoutaudio.ogg