TrueHD -> AC3 bitstreaming

[Thunderbolt8]

I want to remux all my movies to .mkv and only keep a TrueHD track as main audio track. my problem is that my rather old receiver can only do DTS and AC3 via SPDIF.

in case of muxing DTS-HD MA this is not a problem, because of the included dts core track. bitstreaming via reclock & mpc-hcs internal dts audio decoder works fine.

but TrueHD doesnt contain a kind of core track (also not included in matroska specs; sticking to m2ts is not an option) and since I dont want to redo all my movies in the future because of removing and included separate ac3 track for compatibility reasons I am wondering what possibilities there are to convert TrueHD to AC3 during playback and bitstreaming this to my receiver.

got reclock (bypass resampler setting), LAV audio, ac3 filter and mpc-hcs internal ac3 decoder as options.

what seems to work so far is to tick "use ac-3 encoding" in reclock, then I can use either lav audio or the internal ac3 decoder and my receiver receives the dolby digital signal.

but I dont really know about the quality of reclocks ac3 encoding, how good it is. its a bit like a black box to me. does reclock always encode to 640 kbit/s ac3? is the quality of reclock ac3s encoding comparable or the same as when using eac3to to convert the TrueHD track to AC3? or are there any differences?

what other options do I have here?

[Qaq]

eac3to uses Nero or libav for ac3 decoding and those are not world best. AFAIK you have only 2 options for ac3 encoding on the fly - ffdshow or reclock. There is not much really to discuss here IMO. And you can read reclock's man for details.

[Thunderbolt8]

at reclock forums it says "The AC3 encoder uses the Valex Audio Library (VALib) by Alexander Vigovsky"

so the ac3 encoder is the same of that of ac3filter as it seems. the question is whether that one is of better quality than libav or nero?

is there anything else in the chain which could further diminish the audio quality other than encoding to ac3 at this one step when trying to bitstream & encode thruehd as ac3?

[Qaq]

Maybe best option for you is extract embedded ac3s to additional .ac3 tracks. See: no need to parse, no need to encode, no doubts about SQ.

[Thunderbolt8]

as written in the OP, that is not what I want to do. I dont want to store or keep more tracks other than the original lossless one. dont want to go through my collection and remove all lossy tracks after some time.

so would like to know what is the best possibility under these circumstances.

[Thunderbolt8]

when trying to do this with a 7.1 THD track, it seems the only thing I can use then is ffdshow, because lav audio or the mpc-hc ac3 encoder cant modify the number of channels and 7.1 is not accepted by my receiver.

but with ffdshow audio, I can set output to 3/0/2 + LFE channels in the mixer and then it works. the question for only is what does ffdshow audio do with the sound information of those 2 side channels? does that information get dropped or added to the other channels?