ffmpeg - 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 Adobe Premiere , 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. 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., MP4 to WebM ). Commonly, developers use FFmpeg via the ffmpeg CLI tool, but there are language-specific bindings written for FFmpeg to import it as a package/dependency into your project/s. With ffmpeg , 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. Below, I'm going to show you... Some operating systems already have ffmpeg installed. To check, simply type ffmpeg into the terminal. If the command is already installed, then the terminal prints a synopsis of ffmpeg . If ffmpeg is not yet installed on your machine, then visit the FFmpeg website, navigate to the " Download " page, download a compiled executable (compatible with your operating system) and execute it once the download is complete. Note : It is recommended to install the stable build to avoid unexpected bugs. Alternatively... For extensive documentation, enter the command man ffmpeg , which summons man ual pages for the ffmpeg command: For this blog post, I will demonstrate the versatility of ffmpeg using the Big Buck Bunny 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 ( 30 MB, 640 x 360 ) from Test Videos . The wget 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 Big_Buck_Bunny_360_10s_30MB.mp4 . The -c option tells wget to resume an interrupted download from the most recent download position, and the -O option tells wget to download the file to a location of your choice and customize the name of the downloaded file. The ffmpeg command follows the syntax: For a full list of options supported by ffmpeg , consult the documentation . 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 -i option with a path of the input file ( infile ) to ffmpeg without any infile options. However, to provide any outfile option, ffmpeg must be provided the path of the output file ( outfile ). To specify an input media file, provide its path to the -i 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 ffmpeg command. To print information about a media file, run the following command: Just providing an input media file to the ffmpeg command displays its details within the terminal. Here, the Metadata 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 30k FPS. To strip away the FFmpeg banner information (i.e., the FFmpeg version) from the output of this command, provide the -hide_banner option. That's much cleaner! 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... Note : Depending on your machine's hardware, you may need to be patient for large files! To find out all the formats supported by ffmpeg , run the following command: 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: Here, we specify a video filter with the -vf 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. Note : To preserve aspect ratio, you need to set either the target width or height to -1 (i.e., scale=360:-1 sets the width to 360px and the height to a value calculated based on this width and the video's aspect ratio). The output file is less than 100 KBs! Here, we specify the H.265 video codec by setting the -c:v option to libx265 . The -preset defines the speed of the encoding. The faster the encoding, the worst the compression, and vice-versa. The default preset is medium , but we set it to fast , which is just one level above medium in terms of speed. The CRF is set to 28 for the default quality maintained by the codec. The -tag:v option is set to hvc1 to allow QuickTime to play this video. 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! Unfortunately, because browser support for H.265 is sparse , videos compressed with this standard cannot be viewed within most major browsers (e.g., Chrome and Firefox). Instead, use the H.264 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 all major browsers . Note : We don't need to provide the additional -tag:v option since QuickTime automatically knows how to play videos compressed with H.264. Note : 23 is the default CRF value for H.264 (visually corresponds to 28 for H.265, but the size of a H.264 compressed file will be twice that of a H.265 compressed file). Notice that the resulting video ( Big_Buck_Bunny_360_10s_30MB_codec_2.mp4 ) is now twice that of previous ( Big_Buck_Bunny_360_10s_30MB_codec.mp4 ), 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. Big_Buck_Bunny_360_10s_30MB_codec_2.mp4 in Firefox: Big_Buck_Bunny_360_10s_30MB_codec.mp4 in Firefox: Check out this codec compatibility table 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 ffmpeg , run the following command: First, let's download another video, the ten second Jellyfish MP4 video ( 30 MB, 640 x 360 ), from Test Videos. To concatenate this video to the Big Buck Bunny video, run the following command: 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 demuxer , 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 -c copy ), the command quickly concatenates the files with no loss in quality. Note : Setting the -safe option to 0 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. When you play the concatenated.mp4 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. Note : 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. 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 ffmpeg . Then, we specify the video codec ( -c:v ) to be copy to tell FFmpeg to copy the video's bitstream directly to the output with zero quality changes, and we specify the audio codec ( -c:a ) to be aac (for Advanced Audio Coding ) 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 -c:a 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 -shortest option to tell FFmpeg to stop encoding once the shortest input file (in this case, the ten second Big Buck Bunny video) is finished. Additionally, download the audio file Ukulele from Bensound . 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 -stream_loop option to FFmpeg. Set its value to -1 to infinitely loop over the input stream. Note : The -stream_loop option is applied to the input file that comes directly after it in the command, which happens to be the short.mp3 file. This audio file has a duration less than the video file. Consult the FFmpeg Documentation to learn more about all of the different video processing techniques it provides.