user21449: For some reason, my ffmpeg output log does not show dup and drop key-value pairs.
expect:
...
frame=563 fps=138 q=23.0 size=13056kB time=00:00:09.42 bitrate=11346.8kbits/s dup=0 drop=0 speed= 2.3x
...

running the following:
~/bin/ffmpeg -i INPUT.mkv \
    -t 00:00:10.000 \
    -c:v libx264 -crf 15 -preset veryfast \
    OUTPUT.mkv 2>&1|tee ffmpeg.log

results in this output instead:
...
frame=  563 fps=138 q=23.0 size=   13056kB time=00:00:09.42 bitrate=11346.8kbits/s speed= 2.3x
frame=  600 fps=134 q=-1.0 Lsize=   16199kB time=00:00:09.98 bitrate=13294.4kbits/s speed=2.23x
video:16095kB audio:92kB subtitle:0kB other streams:0kB global headers:4kB muxing overhead: 0.077694%
[libx264 @ 0x55d5711efac0] frame I:3     Avg QP:15.71  size:227164
...

or running:
~/bin/ffmpeg -f v4l2 \
    -framerate 60 -video_size 1920x1080 \
    -input_format mjpeg -i /dev/video0 \
    -c:v libx264 -crf 15 -preset veryfast \
    -tune film -profile:v high -pix_fmt yuv420p \
    -color_primaries 1 -color_trc 1 -colorspace 1 \
    -dst_range 1 -color_range 2 \
    OUTPUT.mkv 2>&1|tee ffmpeg.log

gives:
...
frame=  880 fps= 60 q=23.0 size=   64512kB time=00:00:14.31 bitrate=36910.3kbits/s speed=0.977x
frame=  911 fps= 60 q=23.0 size=   64512kB time=00:00:14.83 bitrate=35626.4kbits/s speed=0.978x

system info

OS: Linux Debian 10 (buster) x86_64
tested with two versions of ffmpeg:

1) Debian package
$ ffmpeg -version
ffmpeg version 4.1.4-1~deb10u1 built with gcc 8 (Debian 8.3.0-6)

2) compiled for myself
$ ~/bin/ffmpeg -version
ffmpeg version N-97910-g88567a2 built with gcc 8 (Debian 8.3.0-6)

using -loglevel debug and ffv1
~/bin/ffmpeg -i INPUT.mkv \
    -t 00:00:10.000     \
    -acodec  copy       \
    -vcodec  ffv1       \
    -level 1 -coder 1 -context 1 -g 1 \
    -loglevel debug     \
    OUTPUT.mkv 2>&1|tee ffmpeg.log

result: unable to find a single occurrence of the word "drop" in log.txt file
How to output the missing "dup" and "drop" in my log?

user1871: If no frames are dupped or dropped, then those fields are not printed.
If you need a definitive statement, add -progress filename to print progress report to a file and search for dup_frames and drop_frames.

21449: <p>For some reason, my ffmpeg output log does not show <strong>dup</strong> and <strong>drop</strong> key-value pairs.</p>

<p>expect:</p>

<pre><code>...
frame=563 fps=138 q=23.0 size=13056kB time=00:00:09.42 bitrate=11346.8kbits/s dup=0 drop=0 speed= 2.3x
...
</code></pre>

<p>running the following:</p>

<pre><code>~/bin/ffmpeg -i INPUT.mkv \
    -t 00:00:10.000 \
    -c:v libx264 -crf 15 -preset veryfast \
    OUTPUT.mkv 2&gt;&amp;1|tee ffmpeg.log
</code></pre>

<p>results in this output instead:</p>

<pre><code>...
frame=  563 fps=138 q=23.0 size=   13056kB time=00:00:09.42 bitrate=11346.8kbits/s speed= 2.3x
frame=  600 fps=134 q=-1.0 Lsize=   16199kB time=00:00:09.98 bitrate=13294.4kbits/s speed=2.23x
video:16095kB audio:92kB subtitle:0kB other streams:0kB global headers:4kB muxing overhead: 0.077694%
[libx264 @ 0x55d5711efac0] frame I:3     Avg QP:15.71  size:227164
...
</code></pre>

<p>or running:</p>

<pre><code>~/bin/ffmpeg -f v4l2 \
    -framerate 60 -video_size 1920x1080 \
    -input_format mjpeg -i /dev/video0 \
    -c:v libx264 -crf 15 -preset veryfast \
    -tune film -profile:v high -pix_fmt yuv420p \
    -color_primaries 1 -color_trc 1 -colorspace 1 \
    -dst_range 1 -color_range 2 \
    OUTPUT.mkv 2&gt;&amp;1|tee ffmpeg.log
</code></pre>

<p>gives:</p>

<pre><code>...
frame=  880 fps= 60 q=23.0 size=   64512kB time=00:00:14.31 bitrate=36910.3kbits/s speed=0.977x
frame=  911 fps= 60 q=23.0 size=   64512kB time=00:00:14.83 bitrate=35626.4kbits/s speed=0.978x
</code></pre>

<p>system info</p>

<ul>
<li>OS: Linux Debian 10 (buster) x86_64</li>
<li>tested with two versions of ffmpeg:</li>
</ul>

<p>1) Debian package</p>

<pre><code>$ ffmpeg -version
ffmpeg version 4.1.4-1~deb10u1 built with gcc 8 (Debian 8.3.0-6)
</code></pre>

<p>2) compiled for myself</p>

<pre><code>$ ~/bin/ffmpeg -version
ffmpeg version N-97910-g88567a2 built with gcc 8 (Debian 8.3.0-6)
</code></pre>

<p>using <code>-loglevel debug</code> and <code>ffv1</code></p>

<pre><code>~/bin/ffmpeg -i INPUT.mkv \
    -t 00:00:10.000     \
    -acodec  copy       \
    -vcodec  ffv1       \
    -level 1 -coder 1 -context 1 -g 1 \
    -loglevel debug     \
    OUTPUT.mkv 2&gt;&amp;1|tee ffmpeg.log
</code></pre>

<p>result: unable to find a single occurrence of the word "drop" in log.txt file</p>

<p>How to output the missing "<strong>dup</strong>" and "<strong>drop</strong>" in my log?</p>
 1871: <p>If no frames are dupped or dropped, then those fields are not printed.</p>

<p>If you need a definitive statement, add <code>-progress filename</code> to print progress report to a file and search for <code>dup_frames</code> and <code>drop_frames</code>.</p>
