MP4(3)

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

okay so this is a page from the MP4 File Format Library manual — third section, library calls, you know the vibe. today's main character is MP4ReadRtpHint, and she's about to hand you an RTP hint like it's a note passed in class. 🎀

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✨ NAME ✨

MP4ReadRtpHint — read an RTP hint. that's it. that's the whole job. 💅

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🌸 SYNTAX 🌸

first things first, you gotta invite her in:

#include <mp4.h>

bool MP4ReadRtpHint(
     MP4FileHandle hFile,
     MP4TrackId trackId,
     MP4SampleId sampleId,
     u_int16_t* pNumPackets = NULL
);

look at that signature. she's giving organized. 🦋

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🫶 ARGUMENTS 🫶

here's the group chat roll call, no one gets left on read:

• hFile — which mp4 file we're doing this whole operation on. the file. your file. 🍓
• trackId — which hint track we're working with. specify her by id, bestie.
• sampleId — which hint sample you wanna read. ⚠️ caveat, and this one is so real: the first sample has id 1, not 0. yes, really. she starts at one. not zero. do not come for me, that's just how she is. 😭
• pNumPackets — a pointer to a variable that will hold the number of packets in the hint. she's the container, you're the recipient. it's giving ✨delivery✨.

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👑 RETURN VALUES 👑

• if it works out: true (1). slay. 💖
• if it does not work out: false (0). it's giving heartbreak. 💀

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🌈 DESCRIPTION 🌈

MP4ReadRtpHint reads the hint sample you asked for from the hint track you asked for, and — this is the important part — it sets you up so that subsequent calls to MP4ReadRtpPacket() can read the individual RTP packets associated with this hint. so like, this is the setup, MP4ReadRtpPacket() is the payoff. teamwork makes the dream work. 🧚

and if you want it? the number of RTP packets associated with this hint gets returned to you. you asked, she delivered. periodt. 💅

now for the part that lowkey blew my mind: a hint track sample is just like any other track sample. i.e. MP4ReadSample(), MP4GetSampleSize(), MP4GetSampleTime(), etc. — all valid, all working, no special treatment, no exclusive club. 🔥

the RTP-specific functions exist because somebody has to interpret the information contained in the hint track samples — those samples are literally carrying instructions on how to form the actual RTP packets. so the hint sample is the recipe, and the RTP functions are the ones who read the recipe and cook. 🍳

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💜 SEE ALSO 💜

• MP4(3)
• MP4ReadRtpPacket(3)

go read those too, bestie, they're in the same friend group. 🦋

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ngl if you're deep in hint tracks and RTP packets, you're doing something very cool and i'm obsessed with you. iykyk. 🫶

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Cisco Systems Inc. wrote this one, it's Version 0.9, and it's been sitting in the MP4(3) section since forever. mwah, thank you for your service, iconic behavior. 💖✨🎀