<glacius:metadata>

    <title>ffmpeg snippets</title>

    <description>Scripts for doing stuff with ffmpeg</description>

    <category>Programming</category>

    <category>ffmpeg</category>

    <category>Bash</category>

    <category>Code snippets</category>

</glacius:metadata>

<h2>Extract single frame as image</h2>

<glacius:code lang="bash"><![CDATA[

# extract image from a video at timestamp 1:16

# use -q:v <num> for jpeg quality control

ffmpeg -i video.mp4 -ss 01:16 -frames:v 1 image.jpeg

]]></glacius:code>

<p>

    See <a href="https://superuser.com/a/324596">this Super User answer</a> for

    quality details, apparently the values of <code>-qscale</code> are between 1 and 31

    for jpegs. PNG is lossless so won't be affected by quality. The <code>v</code>

    in <code>q:v</code> refers to the video stream. From the man page:

</p>

<blockquote>

    <p>

        Use fixed quality scale (VBR). The meaning of q/qscale is codec-dependent.

        If qscale is used without a stream_specifier then it applies only to the

        video stream, this is to maintain compatibility with previous behavior and

        as specifying the same codec specific value to 2 different codecs that is

        audio and video generally is not what is intended when no stream_specifier

        is used.

    </p>

</blockquote>

<h2>Fixing Firefox's "corrupt MP4" issue</h2>

<p>

    Firefox can't handle something about yuv444 chroma sampling (it will probably

    say something in the console about being unable to decode it).

</p>

<blockquote><p>

    Decoder may not have the capability to handle the requested video format with 

    YUV444 chroma subsampling

</p></blockquote>

<p>

    Fix it by using the <code>-pix_fmt</code> option, e.g.

</p>

<glacius:code lang="bash"><![CDATA[

ffmpeg \

  -i input.mp4 \

  -pix_fmt yuv420p \

  -c:a copy \

  output.mp4

]]></glacius:code>

<h2>Fade out video and/or audio</h2>

<p>

    Add a 2-second fade-in from the beginning and a 2-second fade-out

    from the end of an 81 second video:

</p>

<glacius:code lang="bash"><![CDATA[

ffmpeg -i input.mp4 \

  -filter:a afade=t=in:d=2:st=0,afade=t=out:d=2:st=79 \

  -filter:v fade=t=in:d=2:st=0,fade=t=out:d=2:st=79 \

  output.mp4

]]></glacius:code>