anal_annexb.c

anal_annexb.c

#include <stdint.h>
#include <stdbool.h>

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

FILE* fp;
size_t N;
uint8_t* buf;

int main(int argc, char** argv) {
    if(argc < 2) {
        printf("USAGE: anal_annexb filename");
        return 1;
    }

    fp = fopen(argv[1], "rb");
    assert(fp);

    int rc;
    rc = fseek(fp, 0, SEEK_END);
    assert(!rc);
    N = ftell(fp);
    rc = fseek(fp, 0, SEEK_SET);
    assert(!rc);

    buf = malloc(N);
    assert(buf);
    rc = fread(buf, 1, N, fp);
    assert(rc == N);

    int prev_nalu = -1;

    for(int i=0; i<N-3; i++) {
        bool found = false;
        int start = i;
        if(buf[i]==0 && buf[i+1] == 0 && buf[i+2] == 0 && buf[i+3] == 1) {
            found = true;
            start += 4;
        } else if (buf[i]==0 && buf[i+1] == 0 && buf[i+2] == 1) {
            found = true;
            start += 3;
        }

        if(found && start != prev_nalu) {
            prev_nalu = start;
            uint8_t header = buf[start];
            printf("nal unit at offset %d header 0x%02x\n", start, header);
        }
    }

    fclose(fp);
    return 0;
}