MP4(3)

📦 version 2.1.0, in fedora 43, fedora 44

💖 MP4GetRtpPacketTransmitOffset — from the MP4 File Format Library (that's section 3 of the manual, bestie) 🎀

okay so real talk, this is a page from the MP4 File Format Library manual, and today's main character is a lil function called MP4GetRtpPacketTransmitOffset. It's giving "quiet overachiever" — tiny, does one thing, does it flawlessly. 💅

✨ NAME ✨

MP4GetRtpPacketTransmitOffset</purole> — get the transmit offset of an RTP packet 🦋

(no like literally, that's its whole job, and it's obsessed with it)

🌸 SYNTAX 🌸

so first you gotta pull in the header, obviously:

#include <mp4.h>

and then here's the whole vibe, character for character, don't you dare typo it:

int32_t MP4GetRtpPacketTransmitOffset(
     MP4FileHandle hFile,
     MP4TrackId hintTrackId,
     u_int16_t packetIndex
)

💜 ARGUMENTS 💜

three of them. three lil besties walking into a function. let's meet them:

  • hFile — the mp4 file this whole operation applies to. your file. your baby. 🫶
  • hintTrackId — the hint track it applies to. yes, hint track. very mysterious of it. 🔥
  • packetIndex — the packet it applies to. which packet? that one. the one you just pointed at. 👑

🌈 RETURN VALUES 🌈

it hands you back the transmit offset for the packet you specified, in the hint track timescale. that's it. that's the gift. no cap. ✨

🎀 DESCRIPTION 🎀

okay so here's the tea, bestie: MP4GetRtpPacketTransmitOffset returns the transmit offset of an RTP packet.

and the way that some hinters set this offset is specifically to smooth out the packet transmission times and reduce network burstiness — like, spread things out so the network isn't getting jump-scared by a giant clump of packets all at once. 💀

so if you're a transmitter, you would need to apply this offset to the calculated transmission time that's based on the hint start time. like, you can't just ignore it. it's part of the math. do the math. 🧚

tl;dr — offset + (transmission time calculated from hint start time) = the actual time you send. Don't skip the offset, bestie, it's there for a reason.

🌟 SEE ALSO 🌟

go read these too, they're all in the same friend group:

Cisco Systems Inc. made this, Version 0.9 of it, and this whole page lives in the MP4(3) section of the manual. mwah. bye bestie, go get that offset 💖✨🎀🦋🌸💅🫶

📦 where this page comes from