CODEWITHSUNDEEP
pythoncmp3stm32duration
S2G
S2G

Reputation: 133

get the duration of an MP3 in Microcontroller

Good day

I have been asked to do a project which consist of one STM32 and VS1003 , a FAT32 USB host MP3 player . all the parts are done but now ,I need to get the duration of a song.

unfortunately TLEN is not available on all the songs so i cant count on it. my understanding is an mp3 is made by frames and each frame is 0.026 second , each frame starts with 0XFF 0xFX (X can be any) so i need to search for 0xFFFx in 2 separate bytes and count them, then multiply by 0.026 and get the duration ,

since Microcontroller has limited SRAM file needs to be read 2048 bytes by 2048 bytes from USB , i decided to test this theory in computer by Python first then change it to C on microcontroller (for ease of testing the algorithm), but the numbers i'm getting is a lot more than what is expected .

for example an mp3 gives me 25300 of 0XFF 0XFX which translates to 657.5 Second , but i know that the it in fact is 187 Seconds

it seems that 0XFF 0xFx is in the middle of the song too

is there any reliable way to count the headers ? or is there any other way to get the lenght without counting the header ? any notes or basic code (in python or c or js) is appreciated in advance

Upvotes: 1

Views: 163

Answers (1)

Kevin Boone
Kevin Boone

Reputation: 4307

The frame sync marker is not 0xFFFx where x is any four bits, it's 0xFFFx or 0xFFEx. Because the same patterns can appear in the audio data, a brute-force search for the patterns won't work -- you'll have to find the first instance of the sync marker, and then calculate the byte length of each frame from the bitrate in the frame header. There's a post on that calculation already, here:

Formula from mp3 Frame Length

Upvotes: 2

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