ffmpeg vault ============ [[tech]] [[tools]] #software Essentials ---------- ### What? [ffmpeg](https://ffmpeg.org/) is a swiss army knife for everything audio/video. It can do practically every task under the sun, and in fact powers most major dedicated "video players" (VLC, MPC-HC, built-in players in Chrome and Firefox...)[^1] ### How? If you're on Windows, it's technically possible to install `ffmpeg` and use it directly [^2], but since the windows Command Prompt sucks ass comfort-wise and scripting-wise, it's recommended to just [install Ubuntu as part of the Windows Subsystem for Linux](https://docs.microsoft.com/en-us/windows/wsl/install-win10), and then `apt-get install ffmpeg`. If you're on Linux, you already know what to do 😎 Techniques ---------- (All commands are expected to be ran in `bash` or a similar Linux shell.) ### Basic conversions `ffmpeg` is pretty clever, it can correctly guess the codecs and reasonable default settings by the file extension, so all of the following will work as expected (and retain metadata[^3]!): ``` {.bash} ffmpeg -i video.avi video.mp4 ffmpeg -i video.mp4 video_sound_only.wav ffmpeg -i video_sound_only.wav video_sound_only.mp3 ffmpeg -i song.flac song.mp3 ``` #### mp3 bitrates "Reasonable" might not be what you want though, especially in the case of mp3, where the default bitrate is V4 (!), i.e. 140-185 kbps. If you want, for example, V[0], use the `-q:a`[^4] option, like so: ``` {.bash} ffmpeg -i song.flac -q:a 0 song.mp3 ``` More info at: #### video codecs Since container/format ≠ codec, you might want to select the codec manually. While it can reasonably assumed that `mp4` ≅ `h264`, `avi` is a bit more complex. You can list all the supported codecs with `ffmpeg -codecs`[^5], but since there's several hundreds, you better have an idea of what you want to do in the first place. For example, if you want an `.avi` with xvid codec, you just do: ``` {.bash} ffmpeg -i original.mp4 -c:v libxvid output.avi ``` #### General codec options This StackOverflow post explains everything: ### Streams `ffmpeg` can also smoothly handle streams, so basic stream capture is pretty trivial, provided you grabbed the playlist/HLS url from somewhere[^6]: ``` {.bash} ffmpeg -i "https://example.com/playlist.m3u8" my_stream.mp4 ``` #### Taking a screenshot of a stream `-vframes 1` is the option that tells `ffmpeg` to just capture one (i.e. the first) frame of the video - in the case of streams, this means the latest one anyway. ``` {.bash} ffmpeg -i "https://example.com/playlist.m3u8" -vframes 1 capture.jpg ``` ### dropped frame re-interpolation `ffmpeg` also has a [rich set of filters](https://ffmpeg.org/ffmpeg-filters.html), two of which are of interest for us now: - [mpdecimate](https://ffmpeg.org/ffmpeg-filters.html#mpdecimate) - *Drop frames that do not differ greatly from the previous frame in order to reduce frame rate.* - [minterpolate](https://ffmpeg.org/ffmpeg-filters.html#minterpolate) - *Convert the video to specified frame rate using motion interpolation.* The idea is that `mpdecimate` drops all near-duplicate frames, and `minterpolate` re-calculates them using non-duplicate frames that were left. `mpdecimate`'s defaults are pretty okay, but tohe result may not look too good if the frame drops are frequent and long. I've had pretty good results using its `max` parameter which limits the amount of frames dropped in a single stretch of video, e.g. `-vf mpdecimate=max=15` which drops at most 15 frames (i.e. half a second assuming 30 FPS), meaning interpolation won't happen everywhere and the video will remain faithfully choppy. `minterpolate`, on the other hand, defaults to semi-smart motion compensated interpolation, and that *might* just be what you want, but it generally gives pretty funky results. Fortunately, it also has a "blend" mode, which just averages the start and end frames and crossfades them, which gives much more agreeable outputs for simple frame drop situations. It is also generally much faster, I was getting near or above real-time speeds using "blend", whereas motion compensation dropped the processing speed to 0.01x. **TL;DR**: Full command(s) including the filter pipeline: ``` {.bash} # Fill out all frame drop gaps ffmpeg -i choppy_video.mp4 -vf mpdecimate,minterpolate=mi_mode=blend smoother_video.mp4 # Fill out all frame drop gaps no longer than 10 frames: ffmpeg -i choppy_video.mp4 -vf mpdecimate=max=10,minterpolate=mi_mode=blend smoother_video.mp4 # Motion interpolate the gaps and replicate a bad ketamine trip ffmpeg -i choppy_video.mp4 -vf mpdecimate,minterpolate smoother_video.mp4 ``` ### mp4 compatibility h264 also has "profiles", basically [sets of features](https://en.wikipedia.org/wiki/Advanced_Video_Coding#Profiles) - and it turns out this can make the difference between a file working and not working on some crappy embedded media players, like TVs or pico projectors. > > The `-profile:v` option limits the output to a specific H.264 > > profile. Some devices (mostly very old or obsolete) only support the > > more limited Constrained Baseline or Main profiles. You can set > > these profiles with `-profile:v baseline` or `-profile:v main`. > > ``` {.bash} ffmpeg -i original.mp4 -profile:v baseline output.mp4 ``` And apparently, some players are also sensitive to the pixel format[^7], i.e. can't handle anything else than YUV w/ 4:2:0 chroma subsampling, to fix this use the `-pix_fmt` option as follows: ``` {.bash} ffmpeg -i original.mp4 -pix_fmt yuv420p output.mp4 # or, with the profile settings... ffmpeg -i original.mp4 -profile:v baseline -pix_fmt yuv420p output.mp4 ``` No silver bullet, you'll just have to try different things for different devices. A database of crappy players and appropriate `ffmpeg` settings would be great. ### random --- # Footnotes [^1]: See https://en.wikipedia.org/wiki/FFmpeg#Projects_using_FFmpeg [^2]: from [^3]: like ID3 tags and their FLAC, OGG, WAV, etc. equivalents [^4]: read as -quality:audio [^5]: and respectively, formats with `ffmpeg -formats` [^6]: like ; or just press F12, check the Network tab, and look carefully [^7]: From: https://trac.ffmpeg.org/wiki/Encode/H.264#Encodingfordumbplayers