/k/ /t/ /p/ are all stops, so by definition they STOP. I think it makes much more sense to syllabify it as /hrak.kar/ or /hraʔ.kar/. It seems correct to me as it appears in the dictionary as of today. Other double things that are not stops /s/ /l/, etc. can be LONG because their sounds can be sustained and the nasal stops /n/ /m/ /ng(ŋ)/ can be optionally sustained by 'humming'.
Having done some thinking, voice practising and reading (all to little avail)...
Aye. Stops cannot really be sustained. That is quite clear. I don't think I said anything different. But silence can be sustained. These stops are two-parters. First you close the air flow, then you release it. Normally you do the second part practically instantly after the first, but if you like, you can remain silent for a while - very short while, if you're speaking fast. As this pause is in the middle of a 'phoneme', I don't think it's that silly to speak of a long consonant. From start to finish it can easily take as long as any other sustained phoneme. ...Might be a little bit figurative, s'true.
Now on the other hand, even though the release part is usually the part with the clearest sound, the closing the air flow part
does sound quite different in different stop consonants and may well serve as a phoneme at it's own right. So yeah, to speak of doubled consonant is pretty accurate too. If you pause long enough to differentiate the sounds, you get two consonants at the prize of one stop of the air flow. I think in word combinations like
at times and
top priority even english speakers often do this two for one trick - I do for sure.
As for the IPA notation:
/hrak.kar/ is the simplest possible solution and very defendable. But 1) people not used to doubled consonants will voice two fully executed stops and sound very wrong; 2) If Dothraki also uses fully doubled stops (for example with some prefixes), we'd need to find some different way to notate them.
/hrak:ar/ doesn't seem too popular choice. I saw it used somewhere outside in the internet (with finnish, not with Dothraki of course), but there too it was presented as misleading. Syllabes change in the middle and the notation argues against that.
/hraʔ.kar/ seems like an odd solution. Isn't the ʔ-symbol used unconventionally? As far as I read it marks a stop deep in the throat, a voiceless glottal plosive. You might manage to emulate the way the word sounds quite closely, but if you followed the instruction, you'd do it very wrong and rather awkwardly.
It is, of course, possible that Dothraki just handles doubled stop consonants in some unusual way, but from the little I have heard that doesn't seem likely.
I think for these it's good to listen to DP from the relay text reading from the LCC4 audio. There are some double consonants in the general talk on verb classes too.
Pardon my clumsiness. It seem I either cannot download or haven't even found those recordings. Are they available for an outsider like me?