I have a .flv-file with extremely low volume. I have to turn it to max to be able to hear anything. Is there any way to increase the audio volume on the file itself? I have tried separating the audio from the video, amplifying it, and combine them again. Took forever and reduced the quality of the video. Have also tried ffmpeg with the -vol option. The volume then became just fine, but again, the video sucked after the operation.

The only way to permanently up the volume is to do what you're already doing, extract the audio, boost it, then recombine it with the video.

Since you don't give any details about how you're doing it, I can't say for sure about the video quality issue, except that the command you're using is obviously running it through a conversion also.

If you're keeping the same container format for the output, or another container format that's compatible with the video codec of the input, then you can simply copy the video stream as-is. In ffmpeg "-vcodec copy" should do it.

PS: I've never seen a "-vol" option in ffmpeg. What command did you use exactly?

It worked perfectly when adding the -vcodec copy. Here is the full command:

The site i got it from said the -vol option was poorly documented. It uses binary volume percent, meaning 256 = 100%. It works fine.

Thanks. Problem solved.

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Thanks for the info. Poorly documented is right. It's not listed in the man page at all, nor can I find it listed in the ffmpeg website documentation.

It is mentioned at various places around the web though. I found this page with a list of all the ffmpeg cli options.
http://club.myce.com/f74/ffmpeg-comm...ptions-166608/

It says that vol=256 is the default setting. But I wonder what that means exactly. It would be nice if you could set it to a percentage of the input.

One caution. I discovered when testing it that without setting anything else my input audio changed from 192k mp3 to 64k mp2. You may need to watch it carefully to ensure that you're keeping the audio quality settings you want.

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You're right. According to the command 'ffmpeg -i input.flv', the sound changed from
Stream #0.1: Audio: mp3, 22050 Hz, mono, s16, 32 kb/s
to
Stream #0.1: Audio: adpcm_swf, 22050 Hz, mono, s16

I dont know much about audio, so I'm not sure what this means. Anyway, the quality is good enough for me. No annoying background noise, and I can clearly hear what's going on.

Well, in this case I don't think you need to worry too much, since pcm codecs are generally lossless (actually, I believe pcm itself isn't so much a codec as a specification for how to represent analog sound digitally).

You could have trouble if you need the file to be portable though, since it's possible that there are players not able to handle that codec.

Thank you very much, it works! (And not only for SWF.)

It's still not documented in v0.9.1 but the post was just the thing I needed to increase the gain in some MP4s (w/ AC3 audio) I ripped from DVD.