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Let's say that I have a webm of XMB, and I want to resize it to 2MB in order too upload it to some websites. How can I do it? Is there a website? Can I downsize them in mass?

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Use Avanti with ffmpeg. The former has a job control manager where you drop in multiple files at once and go. You can find webm encoding guide for ffmpeg here: http://trac.ffmpeg.org/wiki/Encode/VP8

Use crf mode encoding and experiment till you get desired size. Set b:v high like 10M and tweak CRF value and if you have no audio, use -an in place of -c:a libvorbis.

Your Avanti GUI should look like this:

enter image description here

Change the crf number (30 in that pic) till you get the size you want.

  • CRF and target bitrate are mutually exclusive. one-pass target bitrate is almost never the best choice, so just use -crf 25 -preset veryslow or something. – Peter Cordes Jul 19 '15 at 18:06
  • With CRF specified, b:v is treated as the max allowable bitrate, not the target bitrate. – Gyan Jul 19 '15 at 19:52
  • No, it isn't. Try with -crf 10 -b:v 200k to prove yourself wrong. If you look in the mediainfo of the output file, you won't see anything in the encoder settings except rc=crf crf=10.0 for rate control. What you're looking for is -maxrate 10M -bufsize 10M, to use x264's VBV settings to cap bitrate. – Peter Cordes Jul 19 '15 at 21:28
  • We're talking about WebM here. Please refer to this sentence in the ffmpeg guide I linked to in my answer: "there's a constant quality mode (like in the x264 encoder) that will ensure that every frame gets the number of bits it deserves to achieve a certain quality level, rather than forcing the stream to have an average bit rate. This results in better overall quality and should be your method of choice when you encode video with libvpx. In this case, the target bitrate becomes the maximum allowed bitrate." – Gyan Jul 20 '15 at 5:11
  • You can also check by setting a low b:v and trying various crf values. When the CRF value leads to a solution lower than b:v, that's the resultant bitrate, otherwise it's close to the b:v – Gyan Jul 20 '15 at 5:15

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