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WebM
WebM support is (hopefully) the newest addition to 4chan. This wiki page is meant to serve as an instructional tool to help you get started converting your content to WebM for posting.
WebM {is being, was} tested in these threads:
- https://rbt.asia/g/thread/S41184007
- https://rbt.asia/g/thread/S41183707
- https://rbt.asia/g/thread/S41178861
- https://rbt.asia/g/thread/S41190521
... and on a few /jp/ threads.
Contents
Converting with ffmpeg
Note: avconv and ffmpeg are not entirely drop-in replacements. Make sure you know which one you are using.
Command Line Options
Below is an ffmpeg command:
ffmpeg -i input.mp4 -c:v libvpx -b:v 1M -c:a libvorbis output.webm
This may look intimidating but it is not all that bad. Let's look at the different parameters:
- -i: Specifies the input file, which you're converting to another format.
- -c:v Specifies the video codec to use. webm isn't actually an encoding type unto itself, but an audio/video container, like mkv. Nevertheless, you will almost always use libvpx for the video.
- -b: Sets the target bitrate. -b:v sets video bitrate and -b:a sets audio. Only use this option if you desire a constant bitrate, which will produce a higher quality file. If you are looking for a smaller file size, consider leaving this out.
- -c:a: Specifies the audio codec to use. Some options include libvorbis, libmp3lame, etc. If you are unsure stick with libvorbis.
Other popular options:
- -threads: Tells ffmpeg to use multithreading. Enter the number of cores your processor has as a parameter or put 0 to use them all.
- -ac: Sets number of audio channels. You should probably not touch this unless you know what you're doing.
- -an: disable audio recording. Use when converting .gif files to .webm.
- -crf: Sets CRF value. Must be from 4-63. Lower is higher quality. 10 is a nice starting point.
- -ss: Seeks to a position in the file. Useful for cutting out small scenes. Takes time in seconds as a parameter or HH:MM:SS syntax. use -to to mark the ending position. For example,
-ss 00:00:00 -to 00:00:10converts the first ten seconds of a video to webm.
Premade Scripts
If you're that lazy, here's a couple premade scripts for video and gif conversion.
Windows
Save these programs as a .bat file and place them in the folder of the video you want to convert. Video to WebM
@echo off
rem about 3megabyte in bit 3*1024*1024*8*0.95
set /A MAXSIZE=23907532
set WIDTH=720
ffmpeg -i %1 2> webm.tmp
for /F "tokens=1,2,3,4,5,6 delims=:., " %%i in (webm.tmp) do (
if "%%i"=="Duration" call :calcLength %%j %%k %%l %%m
)
del webm.tmp
SET /a BITRATE=%MAXSIZE%/%VSECONDS%
ffmpeg -y -i %1 -threads 0 -sn -an -c:v libvpx -b:v %BITRATE% -vf scale=-1:%WIDTH% -quality best -cpu-used 0 -slices 8 -auto-alt-ref 1 -f webm -pass 1 NUL
ffmpeg -y -i %1 -threads 0 -sn -an -c:v libvpx -b:v %BITRATE% -vf scale=-1:%WIDTH% -quality best -cpu-used 0 -slices 8 -auto-alt-ref 1 -f webm -pass 2 "%~n1.webm"
del ffmpeg2pass-0.log > NUL
goto :EOF
:calcLength
FOR /F "tokens=* delims=0" %%A IN ("%3") DO SET /A s=%%A
FOR /F "tokens=* delims=0" %%A IN ("%2") DO SET /A s=s+%%A*60
FOR /F "tokens=* delims=0" %%A IN ("%1") DO SET /A s=s+%%A*60*60
set /A VSECONDS=s
Linux / OS X
If you're using OS X or Linux, you probably know how to save and execute these scripts already, but here's a quick overview:
- Create a file, such as
~/bin/my_script.sh - Copy and paste the code into this file with your favorite editor.
- Open a shell. Run the command
chmod +x ~/bin/my_script.sh - The script can now be called as
~/bin/my_script.sh some_file.typeor if you have your PATH set correctly,my_script.sh some_file.type
Other WebM Creation
Please see Reccomended_software for a list of good software for handling video files such as WebM.
