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151 lines
No EOL
6.5 KiB
Markdown
151 lines
No EOL
6.5 KiB
Markdown
ffmpeg vault
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============
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[[tech]] [[tools]] #software
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Essentials
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----------
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### What?
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[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]
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### How?
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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`.
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If you're on Linux, you already know what to do 😎
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Techniques
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----------
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(All commands are expected to be ran in `bash` or a similar Linux shell.)
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### Basic conversions
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`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]!):
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``` {.bash}
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ffmpeg -i video.avi video.mp4
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ffmpeg -i video.mp4 video_sound_only.wav
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ffmpeg -i video_sound_only.wav video_sound_only.mp3
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ffmpeg -i song.flac song.mp3
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```
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#### mp3 bitrates
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"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.
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If you want, for example, V[0], use the `-q:a`[^4] option, like so:
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``` {.bash}
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ffmpeg -i song.flac -q:a 0 song.mp3
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```
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More info at: <https://trac.ffmpeg.org/wiki/Encode/MP3>
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#### video codecs
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Since container/format ≠ codec, you might want to select the codec manually.
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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.
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For example, if you want an `.avi` with xvid codec, you just do:
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``` {.bash}
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ffmpeg -i original.mp4 -c:v libxvid output.avi
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```
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#### General codec options
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This StackOverflow post explains everything: <https://stackoverflow.com/a/20587693/3833159>
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### Streams
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`ffmpeg` can also smoothly handle streams, so basic stream capture is pretty trivial, provided you grabbed the playlist/HLS url from somewhere[^6]:
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``` {.bash}
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ffmpeg -i "https://example.com/playlist.m3u8" my_stream.mp4
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```
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#### Taking a screenshot of a stream
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`-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.
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``` {.bash}
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ffmpeg -i "https://example.com/playlist.m3u8" -vframes 1 capture.jpg
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```
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### dropped frame re-interpolation
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`ffmpeg` also has a [rich set of filters](https://ffmpeg.org/ffmpeg-filters.html), two of which are of interest for us now:
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- [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.*
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- [minterpolate](https://ffmpeg.org/ffmpeg-filters.html#minterpolate) - *Convert the video to specified frame rate using motion interpolation.*
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The idea is that `mpdecimate` drops all near-duplicate frames, and `minterpolate` re-calculates them using non-duplicate frames that were left.
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`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.
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`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.
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**TL;DR**: Full command(s) including the filter pipeline:
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``` {.bash}
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# Fill out all frame drop gaps
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ffmpeg -i choppy_video.mp4 -vf mpdecimate,minterpolate=mi_mode=blend smoother_video.mp4
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# Fill out all frame drop gaps no longer than 10 frames:
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ffmpeg -i choppy_video.mp4 -vf mpdecimate=max=10,minterpolate=mi_mode=blend smoother_video.mp4
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# Motion interpolate the gaps and replicate a bad ketamine trip
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ffmpeg -i choppy_video.mp4 -vf mpdecimate,minterpolate smoother_video.mp4
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```
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### mp4 compatibility
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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.
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> > The `-profile:v` option limits the output to a specific H.264
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> > profile. Some devices (mostly very old or obsolete) only support the
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> > more limited Constrained Baseline or Main profiles. You can set
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> > these profiles with `-profile:v baseline` or `-profile:v main`.
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>
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> <https://trac.ffmpeg.org/wiki/Encode/H.264#Profile>
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``` {.bash}
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ffmpeg -i original.mp4 -profile:v baseline output.mp4
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```
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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:
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``` {.bash}
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ffmpeg -i original.mp4 -pix_fmt yuv420p output.mp4
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# or, with the profile settings...
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ffmpeg -i original.mp4 -profile:v baseline -pix_fmt yuv420p output.mp4
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```
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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.
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### random
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<https://ottverse.com/ffmpeg-drawtext-filter-dynamic-overlays-timecode-scrolling-text-credits/>
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---
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# Footnotes
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[^1]: See https://en.wikipedia.org/wiki/FFmpeg#Projects_using_FFmpeg
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[^2]: from <https://ffmpeg.zeranoe.com/builds/>
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[^3]: like ID3 tags and their FLAC, OGG, WAV, etc. equivalents
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[^4]: read as -quality:audio
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[^5]: and respectively, formats with `ffmpeg -formats`
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[^6]: like <https://addons.mozilla.org/en-US/firefox/addon/hls-stream-detector/>; or just press F12, check the Network tab, and look carefully
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[^7]: From: https://trac.ffmpeg.org/wiki/Encode/H.264#Encodingfordumbplayers |