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--- ffmpeg:conversions:convert_h264_to_av1:libaom:two-pass [2023/06/15 07:57] – created peter
+++ ffmpeg:conversions:convert_h264_to_av1:libaom:two-pass [2023/06/15 17:43] (current) – peter
@@ Line 1: / Line 1: @@
 ====== ffmpeg - Conversions - Convert H264 to AV1 - libaom - Two-Pass ======
+In order to create more efficient encodes when a particular target bitrate should be reached, two-pass encoding should be used.
+Two-pass encoding is also beneficial for encoding efficiency when constant quality is used without a target bitrate.
+  * For two-pass, you need to run ffmpeg twice, with almost the same settings, except for:
+    * In pass 1 and 2, use the **-pass 1** and **-pass 2** options, respectively.
+    * In pass 1, output to a null file descriptor, not an actual file. (This will generate a logfile that ffmpeg needs for the second pass.)
+    * In pass 1, you can leave audio out by specifying **-an**.
+<code bash>
+time ffmpeg -i a.mp4 -c:v libaom-av1 -b:v 2M -pass 1 -an -f null /dev/null && time ffmpeg -i a.mp4 -c:v libaom-av1 -b:v 2M -pass 2 -c:a libopus -f mp4 out.mp4
+time ffmpeg -i a.mp4 -c:v libaom-av1 -b:v 2000k -pass 1 -an -f null /dev/null && time ffmpeg -i a.mp4 -c:v libaom-av1 -b:v 2000k -pass 2 -ac 2 -c:a libopus  -f mp4 out.mp4x
+</code>
+returns:
+<code bash>
+...
+real	98m40.037s
+user	567m32.622s
+sys	0m26.253s
+</code>
+<WRAP info>
+**NOTE:**
+  * Input test size:  75.5M
+  * Output test size:  4.2M
+</WRAP>
+<WRAP info>
+**NOTE:**  The bitrate limit by the **-b:v** where the bitrate MUST be non-zero.
+  * **Opus** is a totally open, royalty-free, highly versatile audio codec.
+</WRAP>