beta.blog

Determining if an MP4 file is streamable involves checking the arrangement of the file’s metadata, particularly the ‘moov atom’ (a key part of the file’s structure). In a streamable MP4 file, the ‘moov atom’ is placed at the beginning of the file, allowing playback to start before the file is fully downloaded. In a non-streamable file, the ‘moov atom’ is typically at the end, meaning the entire file must be downloaded before playback can begin.

In a HEX editor, this could look something like this:

Of course, we can also write a Go program to check this fact.

package main

import (
	"fmt"
	"os"
)

func isStreamableMP4(filePath string) (bool, error) {
	file, err := os.Open(filePath)
	if err != nil {
		return false, err
	}
	defer file.Close()

	const bufferSize = 1024
	buffer := make([]byte, bufferSize)

	_, err = file.Read(buffer)
	if err != nil {
		return false, err
	}

	for i := 0; i < len(buffer)-4; i++ {
		if string(buffer[i:i+4]) == "moov" {
			return true, nil
		}
	}

	return false, nil
}

func main() {
	if len(os.Args) < 2 {
		fmt.Println("Usage: ./stremable <path_to_mp4_file>")
		return
	}

	filePath := os.Args[1]
	streamable, err := isStreamableMP4(filePath)
	if err != nil {
		fmt.Println("Error checking file:", err)
		return
	}
	if streamable {
		fmt.Println("The file is streamable.")
	} else {
		fmt.Println("The file is not streamable.")
	}
}