Learn Hardcore Turkish: Bu arada, yaya geçidinde bekliyorum; toplantı kaydını telefondan ben başlatıyorum. - By the way, I’m waiting at the crosswalk; I’m starting the meeting recording from my phone.

As “by the way,” Bu arada introduces a side remark or a new, loosely related topic.
As “in the meantime/meanwhile,” it situates the action in a time window overlapping with something else.

Here, given the ongoing actions, either nuance can work. If you want strictly “during this time,” you can also use Bu sırada or Bu esnada, which are more purely temporal and less “topic-shifting” than Bu arada.

Why is there a semicolon (;) between the clauses? Could I use something else?

A semicolon in Turkish works much like in English: it links two closely related independent clauses. You could instead use:

A period: Bu arada, yaya geçidinde bekliyorum. Toplantı kaydını telefondan ben başlatıyorum.
The conjunction ve (and): Bu arada, yaya geçidinde bekliyorum ve toplantı kaydını telefondan ben başlatıyorum. All are acceptable; the semicolon just keeps the tight connection without using a conjunction.

Why is it yaya geçidinde and not something like yaya geçitte?

Because yaya geçidi is an indefinite noun compound (“pedestrian crossing” as a fixed unit). In such compounds, the second noun takes a 3rd‑person possessive suffix. Then you add the locative case to that form:

yaya geçit
- 3rd‑person possessive -i → yaya geçid-i
plus locative -nde → yaya geçid-inde

So it’s not the bare noun geçit with the locative; it’s the compound yaya geçidi with the locative on top.

Where does the -nde in geçidinde come from? I thought the locative was -de/-da or -te/-ta.

The locative is indeed -de/-da (or -te/-ta after voiceless consonants). However, when a noun already has a 3rd‑person possessive ending (-ı/-i/-u/-ü), Turkish inserts a buffer -n- before the case ending. So:

geçid-i (3rd‑person possessive) + -de (locative) → geçid-in-de = geçidinde.

Why does geçit become geçid- in geçidi/geçidinde?

Final consonant voicing: when a suffix beginning with a vowel is added, final t in many words becomes d.

geçit → geçidi (because of the vowel-initial possessive -i)
Similarly: kitap → kitabı, kanat → kanadı

What exactly is bekliyorum in terms of tense/aspect?

It’s the present continuous: verb stem + -iyor + personal ending.

bekle- (to wait) + -iyor
- -um → bekliyorum = “I’m waiting (right now).” For habitual statements, you’d use the aorist: beklerim (“I wait/I usually wait”).

Why does toplantı kaydını have that -nı at the end?

Two things are stacked: 1) toplantı kaydı is an indefinite noun compound (“meeting recording”), where the second noun has a 3rd‑person possessive: kayıt → kayd-ı. 2) Because it’s a definite direct object, you add the accusative -(y)ı/-(y)i/-(y)u/-(y)ü. After a 3rd‑person possessive, you insert buffer -n-: kayd-ı-nı.

So toplantı kaydını = “the meeting recording” (as a specific object) with accusative.

Does kaydını mean “his/her recording”? I see the possessive-like -ı there.

In compounds like toplantı kaydı, the -ı on kayıt is a required 3rd‑person possessive marker of the compound pattern; it doesn’t mean “his/her” in the personal sense. Then the final -nı is the accusative. So toplantı kaydını is best understood as “the recording of the meeting” as a unit, marked definite.

Could I drop the accusative and say toplantı kaydı başlatıyorum?

You could, but it changes the meaning: without accusative it sounds indefinite or non-specific (“I’m starting a meeting recording” as an activity). With accusative (toplantı kaydını) it’s a specific, identifiable recording (“I’m starting the meeting’s recording”).

Why başlatıyorum and not başlıyorum?

başlamak = to start (intransitive): başlıyorum = “I’m starting (myself).”
başlatmak = to start something (transitive/causative): başlatıyorum = “I’m starting it.” Since the object is toplantı kaydını, you need the transitive başlatmak.

What does telefondan convey? Why not telefonda or telefonla?

telefondan (ablative “from/through the phone”): you’re initiating it via the phone, from the phone as the source/device.
telefonda (locative “on the phone”): usually “on a phone call” or “on/at the phone” (location).
telefonla (instrumental “with/by phone”): “by phone” (e.g., contacting someone by phone).

Here, telefondan fits the idea “from the phone (app/device).”

Is ben necessary in … ben başlatıyorum?

No; Turkish usually drops subject pronouns because the verb ending shows the person. Ben is used for emphasis/contrast: “I’m the one starting it (not someone else).” Without emphasis, you could just say Toplantı kaydını telefondan başlatıyorum.

Is the word order natural? Where can I put ben and telefondan?

Yes, it’s natural. In Turkish, focused/emphasized elements tend to appear right before the verb. Some options:

Ben toplantı kaydını telefondan başlatıyorum. (emphasis on “I”)
Toplantı kaydını ben telefondan başlatıyorum. (stronger emphasis on “I” doing that specific thing)
Toplantı kaydını telefondan ben başlatıyorum. (also emphasizes “I,” after another adverbial)
Toplantı kaydını telefondan başlatıyorum. (emphasis on “from the phone”)

All are grammatical; the nuance depends on what you want to highlight.

How would I say “from my phone,” “from the computer,” or “on the phone (call)”?

From my phone: telefonumdan
From the computer: bilgisayardan
On the phone (on a call): telefonda
Via/through the phone (more formal): telefon üzerinden

Could I use a different tense like future or a suggestion form?

Yes:

Immediate/ongoing: başlatıyorum (“I’m starting it [now]”)
Planned future: başlatacağım (“I will start it”)
Habitual/neutral statement: başlatırım
Suggestion/voluntative: başlatayım (“Let me start it”)

Can you break down the morphology of the key phrases?

yaya geçidinde: yaya (pedestrian) + geçit
- 3rd‑person possessive -i → geçidi
  - locative with buffer -nde → geçidinde
bekliyorum: bekle- (wait) + -iyor (present continuous) + -um (1st sg)
toplantı kaydını: toplantı (meeting) + kayıt
- 3rd‑person possessive -ı → kaydı
  - accusative with buffer -nı → kaydını
telefondan: telefon
- ablative -dan
ben başlatıyorum: ben (I) + başlat- (to start something) + -ıyor (present continuous) + -um (1st sg)