speedup/down audio using a DTS-HD MA source (ffmpeg)

[incredibilePino]

Hello, I need to speed up/down an audio of a Bluray in order to do a mux. I want to use ffmpeg, (because I use linux and I think ffmpeg does a good job, but I'm ready to use something else if there are reasons to do it) and my goal is to preserve quality as much as possible. I suppose the atempo feature of ffmpeg is a good way to do the process.

I have two tracks: 1 DTS-HD MA and 1 E-AC-3. I want to speed up/down both. I know how to do it with atempo, I have the following doubts about maintaining audio quality:

1) what output codec should I choose if I start from a DTS-HD MA? DTS, AC3, AAC or something else?
2) same question of (1) but starting from E-AC-3
3) should I start from DTS/AC3 extracted core instead of EAC3/DTSHD-MA? I suppose no, because they are lossy codecs.
4) if I'd have only DTS/AC3 sources, what output format should I use? DTS, AC3, AAC or what?

[tebasuna51]

When you need speed up/down an audio always use the best source (question 3), the output format is your choice (no mather what is the input format because you work over uncompressed audio after the speed up/down, questions 1,2,4) but can change with your player audio system:

For stereo source you can select any format, but for multichannel you must have a compatible audio system, for instance a PC conected by HDMI to a receiver can play any format (flac/.../aac 5/7.1) without problems. With spdif conexion maybe you need EAC3/AC3 format.

To preserve quality as much as possible a lossless format (flac or other free encoders can do the job) is the best choice but you can use also (over a lossy coverted source) a lossy encoder. The recommended (best quality/size) codec is AAC using qaac (https://forum.doom9.org/showthread.php?p=424070#post424070)

See also my answer to your post Muxing 2 bluray with different fps: change audio speed or video speed (for quality)? (https://forum.doom9.org/showthread.php?p=1964437#post1964437)