====== ffmpeg - Conversions - Convert H264 to AV1 - libaom - Constrained Quality ======

**libaom-av1** has a constrained quality (CQ) mode that will ensure that a constant (perceptual) quality is reached while keeping the bitrate below a specified upper bound or within a certain bound.

  * This method is useful for bulk encoding videos in a generally consistent fashion. 

----

<code bash>
time ffmpeg -i a.mp4 -c:v libaom-av1 -crf 30 -b:v 2000k -f mp4 out.mp4
</code>

returns:

<code bash>
...
real	104m57.062s
user	599m4.884s
sys	0m32.345s
</code>

<WRAP info>
**NOTE:** 

  * Input test size:  75.5M
  * Output test size:  4.8M

</WRAP>


<WRAP info>
**NOTE:**  The quality is determined by the **-crf**, and the bitrate limit by the **-b:v** where the bitrate MUST be non-zero.

  * **crf**:  This value can be from 0–63.
    * Lower values mean better quality and greater file size.
    * 0 means lossless.
    * A CRF value of 23 yields a quality level corresponding to CRF 19 for x264 (​source), which would be considered visually lossless.

</WRAP>