cmov.c

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

static size_t get_atom_size(uint8_t* atom)
{
	return (atom[0] << 24) | (atom[1] << 16) | (atom[2] << 8) | atom[3];
}

static void set_atom_size(uint8_t* atom, size_t atom_size)
{
	atom[0] = (atom_size >> 24) & 0xff;
	atom[1] = (atom_size >> 16) & 0xff;
	atom[2] = (atom_size >> 8) & 0xff;
	atom[3] = atom_size & 0xff;
}

int main(int argc, char** argv)
{
	FILE *in = fopen(argv[1], "rb");
	FILE *out = fopen(argv[2], "wb+");
	uint8_t atom[8];
	size_t len = fread(atom, sizeof(atom), 1, in);
	uint8_t buffer[4096];
	while (len > 0)
	{
		size_t atom_size = get_atom_size(atom);
		printf("%d %c%c%c%c\n", (int)atom_size, atom[4], atom[5], atom[6], atom[7]);
		if (atom[4] == 'm' && atom[5] == 'o' && atom[6] == 'o' && atom[7] == 'v')
		{
			// compress the header
			// read all the moov header
			uint8_t *moov = (uint8_t *)malloc(sizeof(uint8_t) * (atom_size - 8));
			size_t bytes_read = fread(moov, 1, atom_size - 8, in);
			if (bytes_read != atom_size - 8)
			{
				// failure, fallback to bypass
				fwrite(atom, sizeof(atom), 1, out);
				fwrite(moov, 1, bytes_read, out);
			} else {
				z_stream strm = {
					.next_in = (Bytef *)moov,
					.avail_in = bytes_read,
					.total_out = 0,
					.opaque = 0,
					.zalloc = Z_NULL,
					.zfree = Z_NULL,
				};
				assert(deflateInit(&strm, 1) == Z_OK);
				uint8_t *cmov = (uint8_t *)malloc(sizeof(uint8_t) * (atom_size - 8));
				size_t cmov_size = atom_size - 8;
				int done = 0;
				while (!done)
				{
					if (strm.total_out >= cmov_size) {
						cmov_size += (atom_size - 8 + 1) / 2;
						cmov = (uint8_t *)realloc(cmov, cmov_size);
					}
					strm.next_out = (Bytef *)cmov + strm.total_out;
					strm.avail_out = cmov_size - strm.total_out;
					int status = deflate(&strm, Z_FINISH);
					if (status == Z_STREAM_END)
						done = 1;
					else if (status != Z_OK)
						break;
				}
				printf("cmov: %d => %d\n", (int)atom_size - 8, (int)strm.total_out);
				if (deflateEnd(&strm) == Z_OK && done)
				{
					set_atom_size(atom, strm.total_out + 40);
					fwrite(atom, sizeof(atom), 1, out);
					set_atom_size(atom, strm.total_out + 32);
					atom[4] = 'c', atom[5] = 'm', atom[6] = 'o', atom[7] = 'v';
					fwrite(atom, sizeof(atom), 1, out);
					set_atom_size(atom, 12);
					atom[4] = 'd', atom[5] = 'c', atom[6] = 'o', atom[7] = 'm';
					fwrite(atom, sizeof(atom), 1, out);
					uint8_t zlib[4];
					zlib[0] = 'z', zlib[1] = 'l', zlib[2] = 'i', zlib[3] = 'b';
					fwrite(zlib, sizeof(zlib), 1, out);
					set_atom_size(atom, strm.total_out + 12);
					atom[4] = 'c', atom[5] = 'm', atom[6] = 'v', atom[7] = 'd';
					fwrite(atom, sizeof(atom), 1, out);
					set_atom_size(zlib, atom_size);
					fwrite(zlib, sizeof(zlib), 1, out);
					fwrite(cmov, 1, strm.total_out, out);
				} else {
					// failure case
					fwrite(atom, sizeof(atom), 1, out);
					fwrite(moov, 1, bytes_read, out);
				}
				free(cmov);
			}
			free(moov);
		} else {
			// bypass this atom
			fwrite(atom, sizeof(atom), 1, out);
			int i;
			for (i = 0; i < atom_size - 8; i += 4096)
			{
				size_t bytes_expected = 4096 < atom_size - 8 - i ? 4096 : atom_size - 8 - i;
				size_t bytes_read = fread(buffer, 1, bytes_expected, in);
				fwrite(buffer, 1, bytes_read, out);
				if (bytes_read < bytes_expected)
					break;
			}
		}
		len = fread(atom, sizeof(atom), 1, in);
	}
	fclose(out);
	fclose(in);
	return 0;
}