 - Thumbnail and Preview Clip Generation (Part 2)

 - If you are unfamiliar with FFmpeg, then please read this 

When you upload a video to a platform such as 

, you can select and add a custom thumbnail image to display within its result item. Amongst the many recommended videos, a professionally-made thumbnail captures the attention of undecided users and improves the chances of your video being played. At a low-level, a thumbnail consists of an image, a title and a duration (placed within a faded black box and fixed to the lower-right corner):

To generate a thumbnail from a video with 

 filter by extracting the thumbnail image from the beginning of the video and writing "Test Text" to the center of this image. This thumbnail image will be a JPEG file.

$ ffmpeg -i ./Big_Buck_Bunny_360_10s_30MB.mp4 -vf "drawtext=text='Test Text':fontcolor=white:fontsize=75:x=(w-tw)/2:y=(h-th)/2" -ss 00:00:09.000 -vframes 1 thumbnail.jpg

Now that we've covered the basics, let's add a duration to this thumbnail:

$ DURATION=$(ffmpeg -i ./Big_Buck_Bunny_360_10s_30MB.mp4 2>&1 | grep Duration | cut -c 13-20)
$ ffmpeg -i ./Big_Buck_Bunny_360_10s_30MB.mp4 -vf "drawtext=text='Test Text':fontcolor=white:fontsize=75:x=(w-tw)/2:y=(h-th)/2,drawtext=text=\'$DURATION\':x=(w-tw)/2:y=h-(2*lh):fontsize=36:fontcolor=white:box=1:boxcolor=black" -ss 00:00:09.000 -vframes 1 thumbnail.jpg

Unfortunately, there's no convenient variable like 

 for accessing the input's duration. Therefore, we must extract the duration from the input's information, which is outputted by the 

). We pipe the information outputted by the 

 to search for the line containing the text "Duration" and pipe it to 

 for ten seconds) from this line. This duration is stored within a variable 

 filters to modify the input media: one for writing the title text "Test Text" and one for writing the duration "00:00:10". The filters are comma delimited. To place the duration within a box, provide the 

 to enable it. To set the background color of this box, provide the 

: Alternatively, you could get the video's duration via the 

Writing a Bash Script for Generating Thumbnail

Let's tidy up this thumbnail by substituting the placeholder title with the actual title, uppercasing this title, changing the font to "Open Sans" and moving the duration box to the bottom-right corner. Like the duration, the title must also be extracted from the input media's information. To uppercase every letter in the title, place the 

 symbol of Bash 4 at the end of the title's variable via 

). Since Bash is required for the uppercasing, let's place these commands inside of a 

, which determines how the script will be executed.

To find the location of the Bash interpreter for the shebang, run the following command:

#!/usr/local/bin/bash

DURATION=$(ffmpeg -i ./Big_Buck_Bunny_360_10s_30MB.mp4 2>&1 | grep Duration | cut -c 13-20)
TITLE=$(ffmpeg -i ./Big_Buck_Bunny_360_10s_30MB.mp4 2>&1 | grep title | cut -c 23-)
UPPERCASE_TITLE=$(echo ${TITLE^^})
ffmpeg -i ./Big_Buck_Bunny_360_10s_30MB.mp4 -vf "drawtext=fontfile=/Users/<username>/Library/Fonts/OpenSans-Bold.ttf:text='$UPPERCASE_TITLE':fontcolor=white:fontsize=28:x=(w-tw)/2:y=(h-th)/2,drawtext=fontfile=/Users/<username>/Library/Fonts/OpenSans-SemiBold.ttf:text=\'$DURATION\':x=(w-tw-8):y=(h-th-8):boxborderw=8:fontsize=20:fontcolor=white:box=1:boxcolor=black@0.625" -ss 00:00:09.000 -vframes 1 thumbnail.jpg 

To specify a font weight for a custom font, reference that font weight's file as the 

Additionally, several changes were made to the thumbnail box. The box color has a subtle opacity of 0.625. This number (any number between 0 and 1) proceeds the 

. A border width of 8px provides a bit of spacing between the edges of the box and the text itself.

 error, update Bash to version 4+ and verify the Bash shebang correctly points to the Bash executable.

When you hover over a recommended video's thumbnail, a brief clip appears and plays to give you an idea of what the video's content is. With the 

 command, generating a clip from a video is relatively easy. Just provide a starting timestamp via the 

 seeks until it reaches this timestamp, which will serve as the point the clip begins at) and an ending timestamp via the 

 option (from the original video at which the clip should end). Because video previews on Youtube are three seconds long, let's extract a three second segment starting from the four second mark and ending at the seven second mark.

$ ffmpeg -i ./Big_Buck_Bunny_360_10s_30MB.mp4 -ss 00:00:04 -to 00:00:07 clip.mp4

Since the clip lasts for a few seconds, we must re-encode the video (exclude 

) to accurately capture instances when no keyframes exist. To clip a video without re-encoding, 

 must capture a sufficient number of keyframes from the video. Since MP4s are encoded with the 

 is stated under the video's metadata printed by 

), if we assume that there are 250 frames between any two keyframes ("a 

 size of 250"), then for the ten second Big Buck Bunny video with a frame rate of 30 fps, there is one keyframe each eight to nine seconds. Clipping a video less than nine seconds with 

 results in no keyframes being captured, and thus, the outputted clip contains no video (

 option, you must specify the duration rather than the ending timestamp. So instead of 

Overlaying an Image on Top of a Thumbnail

Suppose you want to add your brand's logo, custom-made title graphics or watermark to the thumbnail.  

To overlay such an image on top of a thumbnail, pass this image as an input file via the 

 filter. Position the image on top of the thumbnail accordingly with the 

# ...

ffmpeg -i ./Big_Buck_Bunny_360_10s_30MB.mp4 -i ./watermark-ex.png -filter_complex "drawtext=fontfile=/Users/<username>/Library/Fonts/OpenSans-Bold.ttf:text='$UPPERCASE_TITLE':fontcolor=white:fontsize=28:x=(w-tw)/2:y=(h-th)/2,drawtext=fontfile=/Users/<username>/Library/Fonts/OpenSans-SemiBold.ttf:text=\'$DURATION\':x=(w-tw-8):y=(h-th-8):boxborderw=8:fontsize=20:fontcolor=white:box=1:boxcolor=black@0.625,overlay=x=8/2:y=(main_h-overlay_h-8)" -ss 00:00:09.000 -vframes 1 thumbnail.jpg 

Passing multiple inputs (in this case, a video and watermark image) requires the 

 variables represent the main input's height (from the input video) and the overlay's height (from the input watermark image) respectively. Here, we place the watermark image in the lower-left corner of the thumbnail.

The watermark image looks a bit large compared to the other elements on the thumbnail. Let's scale down the watermark image to half its original size by first scaling it down before any of the existing chained filters are executed.

# ...

ffmpeg -i ./Big_Buck_Bunny_360_10s_30MB.mp4 -i ./watermark-ex.png -filter_complex "[1:v]scale=w=iw/2:h=ih/2 [ovrl],[0:v][ovrl]overlay=x=8/2:y=(main_h-overlay_h-8),drawtext=fontfile=/Users/<username>/Library/Fonts/OpenSans-Bold.ttf:text='$UPPERCASE_TITLE':fontcolor=white:fontsize=28:x=(w-tw)/2:y=(h-th)/2,drawtext=fontfile=/Users/<username>/Library/Fonts/OpenSans-SemiBold.ttf:text=\'$DURATION\':x=(w-tw-8):y=(h-th-8):boxborderw=8:fontsize=20:fontcolor=white:box=1:boxcolor=black@0.625" -ss 00:00:09.000 -vframes 1 thumbnail.jpg 

To scale the watermark image to half its size, we must explicitly tell the 

 filter to only scale this image and not the video. This is done by prepending 

 variables will represent the watermark image's width and height respectively. Once the scaling is done, the scaled watermark image is outputted to 

, which can be referenced by other filters for consumption as a filter input. Because the 

 filter takes two inputs, an input video and an input image overlay, we prepend the 

Imagine having a large repository of videos that needs to be processed and uploaded during continuous integration. Write a Bash script to automate this process.

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