ffmpeg webm creation cheatsheet

create a batch file to launch both ffmpeg and a cheatsheet if you have trouble remembering switches or prefer to use notepad as a scratchpad:
start notepad "C:\webm cheatsheet.txt"
cmd /k "cd /d C:\Program Files\ffmpeg\bin && cls"

# dump subs. dumps full subtitle file.
ffmpeg -i "file.mkv" -an -vn -c:s copy C:\sub.ass
## hardsubbing
## 1) dump subs at the input timecode, trimming the subtitle file to just the portion that you want
ffmpeg -ss 10:00:30 -i input.mkv -t 20 -vn -an -c:s copy C:\sub.ass
## 2) encode the video with input subtitle file location set
ffmpeg -ss 10:00:30 -i input.mkv -t 20 -c:v libvpx -b:v 1M -an -vf subtitle=C:\sub.ass C:\output.webm
# 2-pass encoding
ffmpeg -i FILE.EXT -c:v libvpx -pass 1 -f webm null
ffmpeg -i FILE.EXT -c:v libvpx -pass 2 -f webm C:\bokunopico_2pass.webm
# gif > webm
ffmpeg -i "" -c:v libvpx -crf 4 -b:v 500K C:\.webm
# dump meta
ffmpeg -i input_file -f ffmetadata C:\metadata.txt
# add meta
ffmpeg -i input_file -i C:\metadata.txt -map_metadata 1 output_file
# some switches
-i "C:\path\file.avi" : input file
-ss : timecode to seek to and start encoding at (see seeking mode examples below)
-t : duration of output video in seconds
-to : timecode to stop encoding at. used with -ss. cannot be used when -t is set. unreliable. use -t
-f : output format. not necessary to set most of the time.
-framerate : frames per second. low framerates [1-5] make the video impossible to accurately seek through.
-fs : sets an output filesize value in bytes. video will stop encoding at this value, cutting your clip short if necessary.
-sn -an -vn	: ignore subs/audio/video
-mb_threshold 	: does something
-crf 0		: 4-63 lower is better quality
-qmin 0 -qmax 50 : variable quality. unnecessary.
-threads : for multi-threaded processors. if you do not know what to set this value to, do not use it. can lead to bluescreens.
-c:v libvpx : sets video codec. webm codec is libvpx
-b:v [n][KM]	: video bitrate. value in bits/kilobits/megabits. ex: 1/1K/1M. bitrate formula for a 3MB target filesize: -b:v 3*8388608/N*0.975 (replace N with runtime in seconds)
-c:a libvorbis : audio codec. unused for 4chan webms
-b:a:nnn
-vf scale=-1:480 : sets the scale. [width]:[height]. -1 will automatically calculate its value based on the other value (preserves aspect ratio)
-vf crop=w:h:x:y : -vf crop=1280:544:0:88 protip: screenshot your video and edit it in paint to find these co-ordinates if you must crop
-vf subtitles=sub.ssa : sets subtitle source. if no path is set it is relative to location of ffmpeg.exe
-metadata author="%artist%"
-metadata title="%album%" : some forks of 4chanx can extract metadata. always fill this in with the source name or link to where you found it.
-y : yes to overwrite file prompt (useful when tweaking bitrates)

#chaining crop/scale/subtitle commands. simply use a comma
-vf crop=1280:544:0:88,scale=-1:480

#accurate seeking mode (slow)
ffmpeg -i "file.avi" -ss 00:10:00 etc etc

#quick seeking mode (eliminates an initial pause while encoding as ffmpeg has trouble seeking through long, large video files)
ffmpeg -ss 00:10:00 -i "file.avi" etc etc

protip: windows users can shift+right-click a file > copy as path to get a full path to the file, quotes included, copied to the clipboard.
protip: use CTRL+G in MPC-HC to copy millisecond-accurate timecodes.

#blank command. fill this in and get started making those weebums.
ffmpeg -i  -vf scale=-1:480 -c:v libvpx -b:v 3*8388608/*0.975 -metadata title="" -an -y -threads 8 C:\.webm

#music blank (used for creating sound webms. can accept images instead of video as source)
ffmpeg -i [video/image path goes here] -vf scale=-1:240 -i [audio path goes here] -c:v libvpx -b:v 100k -c:a libvorbis -b:a 128k -y -threads 8 C:\.webm

#album preview blank (i use this to create album crossfades from within foobar2k. i won't explain how to create the crossfade here)
ffmpeg -framerate 7 -loop 1 -i  -c:v libvpx -i  -c:a libvorbis -b:a 96k -b:v 90k -vf scale=-1:512 -shortest -threads 8 -y "C:\ preview.webm"