MP4(3)

💖 MP4(3) — the MP4 File Format Library, bestie edition 💖

okay so real talk, this is one of those pages from the MP4 File Format Library — yes, the MP4(3) manual, she's the whole library, the main character, the moment. and today we're zooming in on one very specific little function that is lowkey iconic for anyone doing hint tracks and RTP stuff. let's get into it, no cap. 🎀

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✨ NAME ✨

MP4SetRtpTimestampStart — bestie, it sets the RTP start time of a hint track. that's it. that's the whole job. 💅

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🌸 SYNTAX 🌸

the vibe check, in code form:

#include <mp4.h>

bool MP4SetRtpTimestampStart(
     MP4FileHandle hFile,
     MP4TrackId hintTrackId,
     MP4Timestamp startTime
);

three args, one bool back, and a whole lot of timestamp destiny. periodt. ✨

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🦋 ARGUMENTS 🦋

so like, here's who's showing up to the function party:

• hFile — this is the mp4 file the operation applies to. like, the actual file, the whole point, the reason we're here. 🫶
• trackId — the hint track that the operation applies to. not any track. this track. she's the chosen one. 👑
• startTime — the desired RTP start timestamp for that hint track. you're literally telling it where to begin. 💜

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🌈 RETURN VALUES 🌈

• on success → true (1). slay. ate. no crumbs. 🎉
• on error → false (0). it's giving sadness, it's giving try again. 😭

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💖 DESCRIPTION 💖

okay so here's the tea, bestie: MP4SetRtpTimestampStart sets the RTP timestamp start of the specified hint track.

typically this is a random value that gets chosen when the first RTP packet is constructed by the MP4 library. like, the library just rolls the dice and picks one, no big deal. but — and this is the part you're gonna wanna remember — the value can be set explicitly for the hint track and stored. ✨

and when is that useful? typically it's used if it's desired that timestamps start at zero. yeah. zero. ground floor. the beginning of all things. 🌱

also, if you wanna go read the whole lore: see IETF RFC 1889 for details regarding RTP timestamps and RTCP. iykyk, it's required reading, go off. 📚

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🔥 SEE ALSO 🔥

• MP4(3) — the whole library, the mothership, the blueprint. 💅
• MP4GetRtpTimestampStart(3) — the other half of this situationship, she reads what this one writes. 💞

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bestie warning: don't just toss values at this and expect magic. the docs say what they say — the start value is typically random unless you set it explicitly and store it, and the classic reason to set it is wanting timestamps that start at zero. no invented tips from me, only facts. 🫶

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and that's the page, babe! this gem of a manpage is brought to you by Cisco Systems Inc., Version 0.9, dated MP4(3) — so yeah, it's been serving the Unix community for a minute and it still looks good. mwah. 💖🎀✨🦋