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Old 14th March 2012, 18:09   #1  |  Link
edwinbradford
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Volume discrepancy between MP4 and Webm

I've a small number of short .avi videos I want to export as mp4 and webm for progressive download. Previously I've used Megui to export to mp4 without problem and I've just installed and got Ffmpeg exporting .webm successfully on Windows.

The webm files are fine but the volume is much lower than the mp4's from the same source material. Does anyone have any simple suggestions for remedying this?

I could use the -vol parameter in Ffmpeg to boost the webm volume but it would be an estimate and shouldn't both audio encoders produce the same volume from the same source?
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Old 16th March 2012, 17:46   #2  |  Link
khagaroth
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If you converted the audio using ffmpeg, that's probably your problem (unless you use a fixed build that uses libvorbis), the built-in vorbis codec in ffmpeg is so bad it can be considered totally broken.
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Old 16th March 2012, 18:30   #3  |  Link
edwinbradford
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Thanks, I read that too, but the article I saw said that it was fundamentally broken in all builds of Ffmpeg up to 0.6, I'm using 0.6 or later, I forget which version but definitely post 0.6. Subsequent to Ffmpeg 0.6 it said it was working fine.

I fixed it by boosting the volume in the Ffmpeg encode to max, it appears to cap the volume before it distorts, its not ideal but it will do.

N.B., I don't get it, Google say they will cease support for mp4 so as a content producer I have to encode my video in webm format for native HTML5 playback but the tools for encoding in webm are half finished. Would it not have been better to release user friendly tools with proper documentation and then announce you will cease support for mp4 after? - Just ranting.

Last edited by edwinbradford; 16th March 2012 at 18:34. Reason: addendum
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Old 16th March 2012, 20:15   #4  |  Link
smok3
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after quite some playing around i end up with:

1. pipe video input using ffmpeg to vpxenc
2. extract input audio + hard replaygain, then encode using oggenc
3. muxing video + audio using mkvmerge
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Last edited by smok3; 17th March 2012 at 12:59.
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Old 16th March 2012, 22:51   #5  |  Link
edwinbradford
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Its the "quite some playing around" I want to avoid But I think you're right, feeding the audio to a separate tool then remuxing it seems like the way to properly encode audio for webm until someone produces an opensource or freeware tool that works properly.
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Old 18th March 2012, 09:20   #6  |  Link
Selur
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Hybrid does what smok3 describes,..
1. convert video with vpxenc or extract video with ffmpeg/mp4box/... depending on the selection
2. extract audio
3. decode audio with ffmpeg -> adjust gain, normalize, downmix, speedup,.. with sox -> convert to X with audio selected settings. all depending on what the user specified
4. mux audio&video with mkvmerge
(only downside: replay gain is not automatically detected and applied,..)

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