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====== ffmpeg - Conversions - Convert H264 to AV1 - libaom - A minimum and maximum bitrate, for streaming ======

**libaom-av1** allows a minimum and maximum bitrate can be specified, instead of a quality target.

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

<WRAP info>
**NOTE:**  When muxing into MP4, you may want to add **-movflags +faststart** to the output parameters if the intended use for the resulting file is streaming.
</WRAP>

----

<code bash>
time ffmpeg -i a.mp4 -c:v libaom-av1 -minrate 500k -b:v 2000k -maxrate 2500k -movflags +faststart -f mp4 out.mp4
</code>

returns:

<code bash>
...
real	104m48.048s
user	592m19.009s
sys	0m34.579s
</code>

<WRAP info>
**NOTE:** 

  * Input test size:  75.5M
  * Output test size:  4.9M

</WRAP>


<WRAP info>
**NOTE:**  The bitrate limit by the **-b:v** where the bitrate MUST be non-zero.

  * **movflags ** & **faststart**:  An MP4 video is composed of various data chunks named atoms which can appear in any order, and an important one is moov atom that stores the detailed video metadata.
    * When the video is streamed online, the browser will request the video and try to find the moov atom.
    * Without it, the browser will waste time making extra requests again and again, even download the entire video.
    * With MP4 Fast Start, by optimizing MP4, moving the moov atom to the beginning of a video, so that browser will easily locate the moov atom to load and play the video faster, it can progressively stream while it's buffering.
    * It does not have to wait for it to finish downloading.
</WRAP>