Strip EBU R128 gain tags when using forced-RG transcoding

[spijet]

Hello @sentriz, long time no see! :)

I was messing around with my encode profiles and found that in some cases (e.g. my music library) source files can have EBU R128 gain tags alongside ordinary ReplayGain tags. If we don't instruct ffmpeg to strip out these tags during RG-enabled transcoding, it can confuse some client apps into thinking that the track has ReplayGain tags and should be processed accordingly.

The main problem is that these R128 tags have a different scale than normal RG ones, and even when left with a value of 0 (zero) it can cause some clients to forcibly apply a whopping +5.0 dB gain to the track, causing clipping and occasional ear bleeding. :)

This PR fixes it by stripping these tags out. I double-checked the result (with mediainfo and Foobar2000) and now there are no rogue gain tags left anymore.

[sentriz]

hi again! thanks for the fix :) this makes sense to me. the next release (#141 ) will hopefully be coming after #63 is fixed

[spijet]

Wow, that was quick! :D

I'll add more PRs tomorrow — my local branch now has a bit more accurate (but tad slower) RG processing and some other quality-of-life additions, like properly specifying the MIME-type when transcoding (on cache hit AND cache miss) and ffmpeg now sending data to gonic in chunks of 16K bytes (this kiiinda helps with TTFB being small). As for now, it's 2 AM in my timezone. :)

[sentriz]

cool! looking forward to see what you have 👍 good night