I have been reading a lot, but still I do not understand these two things:

* It is stated that Wav files encoded with Flac and then decoded to Wav are identical to the original Wav files. ReplayGain, if I understand it right, changes the volume level of tracks, - so how can the decoded file be identical to the original, if the volume level was changed? ReplayGain is usually set by default.

* What is the difference between Flac compression levels? Is it just the issue of speed of encoding/decoding and nothing more (no difference in quality, in playback and seeking speed and quality)?

* ReplayGain is metadata contained in the FLAC file that indicates whether and how the volume should be adjusted during playback. No audio data is changed--this is info for the decoding software only, and can be enabled/disabled by the user. Decompressing a FLAC file into a WAV file yields the original WAV file, bit for bit.

* FLAC compression levels differ in the complexity of the algorithm used to compress the original audio. At higher levels the compression process is more demanding on your hardware and takes longer to complete than a simpler, lower compression scheme, but the resulting file size is normally smaller. Audio quality is the same regardless of the compression level. I suppose higher levels create more overhead during decoding, but I haven't noticed any differences in seeking or such.

Thank you!

Adding to what tropic has already done a good job with; think of the FLAC compression levels like what's used by zip, rar, 7-zip, etc... They're all lossless, just finding more bits to compress, thus taking more CPU power and time.

If you're going with a commandline FLAC encoder, which is at 1.1.4, check out the thread started by "gharris" on hydrogenaudio.org. He has posted many compiles of FLAC for various CPU's. Some will possibly cut off a good amount of encoding time with no detrimental effects. It's worth it.