- Editing Audio and Video Content (Part 1)

Online streaming and multimedia content platforms garner a large audience and consume a disproportionate amount of bandwidth compared to other types of platforms. These platforms rely on content creators to upload, share and promote their videos and music. To process and polish video and audio files, both professionals and amateurs automatically resort to using interactive software, such as Adobe Premiere. Such software features many tools to unleash the creativity of its users, but each comes with its own set of entry barriers (learning curve and pricing) and unique workflows for editing tasks. For example, in 

, to manually concatenate footage together, you create a nested sequence, which involves several steps of creating sequences and dragging and dropping clips into a workspace's timeline.

If you produce lots of content weekly for a platform, such as YouTube, and work on a tight schedule that leaves no extra time for video editing, then you may consider hiring a devoted video editor to handle the video editing for you. Fortunately, you can develop a partially autonomous workflow for video editing by offloading certain tedious tasks to FFmpeg. 

 is a cross-platform, open-source library for processing multimedia content (e.g., videos, images and audio files) and converting between different video formats (i.e., 

). Commonly, developers use FFmpeg via the 

 CLI tool, but there are language-specific bindings written for FFmpeg to import it as a package/dependency into your project/s.

, Bash scripts can automate your workflow with simple, single-line commands, whether it is making montages, replacing a video's audio with stock background music or streamlining bulk uploads. This either significantly reduces or completely eliminates your dependence on a user interface to manually perform these tasks by moving around items, clicking buttons, etc.

 into the terminal. If the command is already installed, then the terminal prints a synopsis of 

 is not yet installed on your machine, then visit the 

" page, download a compiled executable (compatible with your operating system) and execute it once the download is complete. 

: It is recommended to install the stable build to avoid unexpected bugs.

For extensive documentation, enter the command 

For this blog post, I will demonstrate the versatility of 

 video, an open-source, animated film built using Blender. Because downloading from the official Big Buck Bunny website might be slow for some end users, download the ten second Big Buck Bunny MP4 video (

$ wget -c -O ./Big_Buck_Bunny_360_10s_30MB.mp4 "https://test-videos.co.uk/vids/bigbuckbunny/mp4/h264/360/Big_Buck_Bunny_360_10s_30MB.mp4"

 CLI utility downloads files from the web. Essentially, this command downloads the video from Wikimedia Commons to the current directory, and this downloaded video is named 

 to resume an interrupted download from the most recent download position, and the 

 to download the file to a location of your choice and customize the name of the downloaded file. 

$ ffmpeg [options] [[infile options] -i infile]... {[outfile options] outfile}...

. Square brackets and curly braces indicate optional items. Items grouped within square brackets are not required to be mutually exclusive, whereas items grouped within curly braces are required to be mutually exclusive. For example, you can provide the 

 without any infile options. However, to provide any 

 must be provided the path of the output file (

To specify an input media file, provide its path to the 

 option. Unlike specifying an input media file, specifying an output media file does not require an option; it just needs to be the last argument provided to the 

To print information about a media file, run the following command:

$ ffmpeg -i ./Big_Buck_Bunny_360_10s_30MB.mp4

Just providing an input media file to the 

 command displays its details within the terminal. Here, the 

 contains information such as the video's title ("Big Buck Bunny, Sunflower version") and encoder ("Lavf54.20.4"). The video runs for approximately ten and a half minutes at 

To strip away the FFmpeg banner information (i.e., the FFmpeg version) from the output of this command, provide the 

To convert a media file to a different format, provide the outfile path (with the extension of the format).

For example, to convert a MP4 file to an WebM file...

$ ffmpeg -i ./Big_Buck_Bunny_360_10s_30MB.mp4 ./Big_Buck_Bunny_360_10s_30MB.webm

: Depending on your machine's hardware, you may need to be patient for large files!

To find out all the formats supported by 

To reduce the amount of bandwidth consumed by users watching your videos on a mobile browser or save space on your hard/flash drive, compress your videos by:

$ ffmpeg -i ./Big_Buck_Bunny_360_10s_30MB.mp4 -vf "scale=iw/4:ih/4" ./Big_Buck_Bunny_360_10s_30MB_reduced_vf.mp4

Here, we specify a video filter with the 

 option. We pass a scale filter to this option that scales down the video to a quarter of its original width and height. The original aspect ratio is not preserved. 

: To preserve aspect ratio, you need to set either the target width or height to 

 sets the width to 360px and the height to a value calculated based on this width and the video's aspect ratio). 

$ ffmpeg -i ./Big_Buck_Bunny_360_10s_30MB.mp4 -c:v libx265 -preset fast -crf 28 -tag:v hvc1 ./Big_Buck_Bunny_360_10s_30MB_codec.mp4

Here, we specify the H.265 video codec by setting the 

 defines the speed of the encoding. The faster the encoding, the worst the compression, and vice-versa. The default preset is 

 for the default quality maintained by the codec. The 

The output file is less than 500 KBs, and it still has the same aspect ratio and dimensions as the original video while also maintaining an acceptable quality!

, videos compressed with this standard cannot be viewed within most major browsers (e.g., Chrome and Firefox). Instead, use the 

 video codec, an older standard that offers worst compression ratios (larger compressed files, etc.) compared to H.265, to compress videos. Videos compressed with this standard can be played in 

$ ffmpeg -i ./Big_Buck_Bunny_360_10s_30MB.mp4 -c:v libx264 -preset fast -crf 23 ./Big_Buck_Bunny_360_10s_30MB_codec_2.mp4

: We don't need to provide the additional 

 option since QuickTime automatically knows how to play videos compressed with H.264. 

 is the default CRF value for H.264 (visually corresponds to 

 for H.265, but the size of a H.264 compressed file will be twice that of a H.265 compressed file).

), but now, you have a video that can be played within all major browsers. Simply drag and drop these videos into separate tabs of Chrome or Firefox to see this.

 to ensure you choose the appropriate codec based on your videos and the browsers you need to support. 

Much like formats, to find out all the codecs supported by 

First, let's download another video, the ten second Jellyfish MP4 video (

$ wget -c -O ./Jellyfish_360_10s_30MB.mp4 "https://test-videos.co.uk/vids/jellyfish/mp4/h264/360/Jellyfish_360_10s_30MB.mp4"

To concatenate this video to the Big Buck Bunny video, run the following command:

$ echo "file './Big_Buck_Bunny_360_10s_30MB.mp4'\nfile './Jellyfish_360_10s_30MB.mp4'" > video-list.txt
$ ffmpeg -i video-list.txt -f concat -safe 0 -c copy concatenated.mp4 

Since both video files are both MP4s and encoded with the same codec and parameters (e.g., dimensions and time base), they can be concatenated by passing them through a 

, which extracts a list of video files from an input text file and demultiplexes the individual streams (e.g., audio, video and subtitles) of each video files, and then multiplexing the constituent streams into a coherent stream. Essentially, this command concatenates audio to audio, video to video, subtitles to subtitles, etc., and then combines these concatenations together into a single video file. By omitting the decoding and encoding steps for the streams (via 

), the command quickly concatenates the files with no loss in quality.

 allows the demuxer to accept any file, regardless of protocol specification. If you are just concatenating files referenced via relative paths, then you can omit this option.

 video file, you will notice that this video's duration is 20 seconds. It starts with the Big Buck Bunny video, and then immediately jumps to the Jellyfish video at the 10 second mark.

: If the input video files are encoded differently or are not of the same format, then you must re-encode all of the video files with the same codec before concatenating them.

Merging Background Music with a Video Clip's Audio

Suppose you wanted to merge the audio of a video with stock background music to fill the silence. To do this, you must provide the video file and stock background music file as input files for 

 to tell FFmpeg to copy the video's bitstream directly to the output with zero quality changes, and we specify the audio codec (

) to tell FFmpeg to encode the audio to an MP4-friendly format. Since our audio file will be MP3, which can be handled by an MP4 container, you can omit the 

 option. To prevent the video from lasting as long as the two and a half minute audio file, and only lasting as long as the original video, add the 

 option to tell FFmpeg to stop encoding once the shortest input file (in this case, the ten second Big Buck Bunny video) is finished.

$ ffmpeg -i ./Big_Buck_Bunny_360_10s_30MB.mp4 -i ./bensound-ukulele.mp3 -c:v copy -c:a aac -shortest Big_Buck_Bunny_306_10s_30MB_sound.mp4

If your audio file happens have a shorter duration than your video file, and you want to continuously loop the audio file until the end of the video, then pass the 

 to infinitely loop over the input stream.

$ ffmpeg -i ./Big_Buck_Bunny_360_10s_30MB.mp4 -stream_loop -1 -i ./short.mp3 -c:v copy -c:a aac -shortest Big_Buck_Bunny_306_10s_30MB_short_sound.mp4

 option is applied to the input file that comes directly after it in the command, which happens to be the 

 file. This audio file has a duration less than the video file. 

 to learn more about all of the different video processing techniques it provides.

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ffmpeg - Editing Audio and Video Content (Part 1)

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