jo_mpeg is a C++ single header library written by Jon Olick, which creates MPEG-1 videos (without audio). It is listed as a C++ only library in stb’s single header library collection. However, only the & reference format is what makes this library C++ only. Replacing those with simple pointers makes this compile with both C and C++. I’m also a big fan of stb-type of library code, so I converted the library to C.
Full source of the C compatible jo_mpeg.h
/* public domain Simple, Minimalistic, No Allocations MPEG writer - http://jonolick.com
*
* Converted to C by Wladislav Artsimovich https://blog.frost.kiwi/jo-mpeg-in-c
*
* Latest revisions:
* 1.03 (15-08-2024) Reverted color space change from 1.02, as it resulted in
* overscaled color vectors and thus oversaturated colors
* 1.02 (22-03-2017) Fixed AC encoding bug.
* Fixed color space bug (thx r- lyeh!)
* 1.01 (18-10-2016) warning fixes
* 1.00 (25-09-2016) initial release
*
* Basic usage:
* char *frame = new char[width*height*4]; // 4 component. RGBX format, where X is unused
* FILE *fp = fopen("foo.mpg", "wb");
* jo_write_mpeg(fp, frame, width, height, 60); // frame 0
* jo_write_mpeg(fp, frame, width, height, 60); // frame 1
* jo_write_mpeg(fp, frame, width, height, 60); // frame 2
* ...
* fclose(fp);
*
* Notes:
* Only supports 24, 25, 30, 50, or 60 fps
*
* I don't know if decoders support changing of fps, or dimensions for each frame.
* Movie players *should* support it as the spec allows it, but ...
*
* MPEG-1/2 currently has no active patents as far as I am aware.
*
* http://dvd.sourceforge.net/dvdinfo/mpeghdrs.html
* http://www.cs.cornell.edu/dali/api/mpegvideo-c.html
* */
#ifndef JO_INCLUDE_MPEG_H
#define JO_INCLUDE_MPEG_H
#include <stdio.h>
// To get a header file for this, either cut and paste the header,
// or create jo_mpeg.h, #define JO_MPEG_HEADER_FILE_ONLY, and
// then include jo_mpeg.c from it.
// Returns false on failure
extern void jo_write_mpeg(FILE *fp, const unsigned char *rgbx, int width, int height, int fps);
#endif // JO_INCLUDE_MPEG_H
#ifndef JO_MPEG_HEADER_FILE_ONLY
#include <stdio.h>
#include <math.h>
#include <memory.h>
// Huffman tables
static const unsigned char s_jo_HTDC_Y[9][2] = {{4,3}, {0,2}, {1,2}, {5,3}, {6,3}, {14,4}, {30,5}, {62,6}, {126,7}};
static const unsigned char s_jo_HTDC_C[9][2] = {{0,2}, {1,2}, {2,2}, {6,3}, {14,4}, {30,5}, {62,6}, {126,7}, {254,8}};
static const unsigned char s_jo_HTAC[32][40][2] = {
{{6,3},{8,5},{10,6},{12,8},{76,9},{66,9},{20,11},{58,13},{48,13},{38,13},{32,13},{52,14},{50,14},{48,14},{46,14},{62,15},{62,15},{58,15},{56,15},{54,15},{52,15},{50,15},{48,15},{46,15},{44,15},{42,15},{40,15},{38,15},{36,15},{34,15},{32,15},{48,16},{46,16},{44,16},{42,16},{40,16},{38,16},{36,16},{34,16},{32,16},},
{{6,4},{12,7},{74,9},{24,11},{54,13},{44,14},{42,14},{62,16},{60,16},{58,16},{56,16},{54,16},{52,16},{50,16},{38,17},{36,17},{34,17},{32,17}},
{{10,5},{8,8},{22,11},{40,13},{40,14}},
{{14,6},{72,9},{56,13},{38,14}},
{{12,6},{30,11},{36,13}}, {{14,7},{18,11},{36,14}}, {{10,7},{60,13},{40,17}},
{{8,7},{42,13}}, {{14,8},{34,13}}, {{10,8},{34,14}}, {{78,9},{32,14}}, {{70,9},{52,17}}, {{68,9},{50,17}}, {{64,9},{48,17}}, {{28,11},{46,17}}, {{26,11},{44,17}}, {{16,11},{42,17}},
{{62,13}}, {{52,13}}, {{50,13}}, {{46,13}}, {{44,13}}, {{62,14}}, {{60,14}}, {{58,14}}, {{56,14}}, {{54,14}}, {{62,17}}, {{60,17}}, {{58,17}}, {{56,17}}, {{54,17}},
};
static const float s_jo_quantTbl[64] = {
0.015625f,0.005632f,0.005035f,0.004832f,0.004808f,0.005892f,0.007964f,0.013325f,
0.005632f,0.004061f,0.003135f,0.003193f,0.003338f,0.003955f,0.004898f,0.008828f,
0.005035f,0.003135f,0.002816f,0.003013f,0.003299f,0.003581f,0.005199f,0.009125f,
0.004832f,0.003484f,0.003129f,0.003348f,0.003666f,0.003979f,0.005309f,0.009632f,
0.005682f,0.003466f,0.003543f,0.003666f,0.003906f,0.004546f,0.005774f,0.009439f,
0.006119f,0.004248f,0.004199f,0.004228f,0.004546f,0.005062f,0.006124f,0.009942f,
0.008883f,0.006167f,0.006096f,0.005777f,0.006078f,0.006391f,0.007621f,0.012133f,
0.016780f,0.011263f,0.009907f,0.010139f,0.009849f,0.010297f,0.012133f,0.019785f,
};
static const unsigned char s_jo_ZigZag[] = { 0,1,5,6,14,15,27,28,2,4,7,13,16,26,29,42,3,8,12,17,25,30,41,43,9,11,18,24,31,40,44,53,10,19,23,32,39,45,52,54,20,22,33,38,46,51,55,60,21,34,37,47,50,56,59,61,35,36,48,49,57,58,62,63 };
typedef struct {
FILE *fp;
int buf, cnt;
} jo_bits_t;
static void jo_writeBits(jo_bits_t *b, int value, int count) {
b->cnt += count;
b->buf |= value << (24 - b->cnt);
while(b->cnt >= 8) {
unsigned char c = (b->buf >> 16) & 255;
putc(c, b->fp);
b->buf <<= 8;
b->cnt -= 8;
}
}
static void jo_DCT(float *d0, float *d1, float *d2, float *d3, float *d4, float *d5, float *d6, float *d7) {
float tmp0 = *d0 + *d7;
float tmp7 = *d0 - *d7;
float tmp1 = *d1 + *d6;
float tmp6 = *d1 - *d6;
float tmp2 = *d2 + *d5;
float tmp5 = *d2 - *d5;
float tmp3 = *d3 + *d4;
float tmp4 = *d3 - *d4;
// Even part
float tmp10 = tmp0 + tmp3; // phase 2
float tmp13 = tmp0 - tmp3;
float tmp11 = tmp1 + tmp2;
float tmp12 = tmp1 - tmp2;
*d0 = tmp10 + tmp11; // phase 3
*d4 = tmp10 - tmp11;
float z1 = (tmp12 + tmp13) * 0.707106781f; // c4
*d2 = tmp13 + z1; // phase 5
*d6 = tmp13 - z1;
// Odd part
tmp10 = tmp4 + tmp5; // phase 2
tmp11 = tmp5 + tmp6;
tmp12 = tmp6 + tmp7;
// The rotator is modified from fig 4-8 to avoid extra negations.
float z5 = (tmp10 - tmp12) * 0.382683433f; // c6
float z2 = tmp10 * 0.541196100f + z5; // c2-c6
float z4 = tmp12 * 1.306562965f + z5; // c2+c6
float z3 = tmp11 * 0.707106781f; // c4
float z11 = tmp7 + z3; // phase 5
float z13 = tmp7 - z3;
*d5 = z13 + z2; // phase 6
*d3 = z13 - z2;
*d1 = z11 + z4;
*d7 = z11 - z4;
}
static int jo_processDU(jo_bits_t *bits, float A[64], const unsigned char htdc[9][2], int DC) {
for(int dataOff=0; dataOff<64; dataOff+=8) {
jo_DCT(&A[dataOff], &A[dataOff+1], &A[dataOff+2], &A[dataOff+3], &A[dataOff+4], &A[dataOff+5], &A[dataOff+6], &A[dataOff+7]);
}
for(int dataOff=0; dataOff<8; ++dataOff) {
jo_DCT(&A[dataOff], &A[dataOff+8], &A[dataOff+16], &A[dataOff+24], &A[dataOff+32], &A[dataOff+40], &A[dataOff+48], &A[dataOff+56]);
}
int Q[64];
for(int i=0; i<64; ++i) {
float v = A[i]*s_jo_quantTbl[i];
Q[s_jo_ZigZag[i]] = (int)(v < 0 ? ceilf(v - 0.5f) : floorf(v + 0.5f));
}
DC = Q[0] - DC;
int aDC = DC < 0 ? -DC : DC;
int size = 0;
int tempval = aDC;
while(tempval) {
size++;
tempval >>= 1;
}
jo_writeBits(bits, htdc[size][0], htdc[size][1]);
if(DC < 0) aDC ^= (1 << size) - 1;
jo_writeBits(bits, aDC, size);
int endpos = 63;
for(; (endpos>0)&&(Q[endpos]==0); --endpos) { /* do nothing */ }
for(int i = 1; i <= endpos;) {
int run = 0;
while (Q[i]==0 && i<endpos) {
++run;
++i;
}
int AC = Q[i++];
int aAC = AC < 0 ? -AC : AC;
int code = 0, size = 0;
if (run<32 && aAC<=40) {
code = s_jo_HTAC[run][aAC-1][0];
size = s_jo_HTAC[run][aAC-1][1];
if (AC < 0) code += 1;
}
if(!size) {
jo_writeBits(bits, 1, 6);
jo_writeBits(bits, run, 6);
if (AC < -127) {
jo_writeBits(bits, 128, 8);
} else if(AC > 127) {
jo_writeBits(bits, 0, 8);
}
code = AC&255;
size = 8;
}
jo_writeBits(bits, code, size);
}
jo_writeBits(bits, 2, 2);
return Q[0];
}
void jo_write_mpeg(FILE *fp, const unsigned char *rgbx, int width, int height, int fps) {
int lastDCY = 128, lastDCCR = 128, lastDCCB = 128;
jo_bits_t bits = {fp};
// Sequence Header
fwrite("\x00\x00\x01\xB3", 4, 1, fp);
// 12 bits for width, height
putc((width>>4)&0xFF, fp);
putc(((width&0xF)<<4) | ((height>>8) & 0xF), fp);
putc(height & 0xFF, fp);
// aspect ratio, framerate
if(fps <= 24) putc(0x12, fp);
else if(fps <= 25) putc(0x13, fp);
else if(fps <= 30) putc(0x15, fp);
else if(fps <= 50) putc(0x16, fp);
else putc(0x18, fp); // 60fps
fwrite("\xFF\xFF\xE0\xA0", 4, 1, fp);
fwrite("\x00\x00\x01\xB8\x80\x08\x00\x40", 8, 1, fp); // GOP header
fwrite("\x00\x00\x01\x00\x00\x0C\x00\x00", 8, 1, fp); // PIC header
fwrite("\x00\x00\x01\x01", 4, 1, fp); // Slice header
jo_writeBits(&bits, 0x10, 6);
for (int vblock=0; vblock<(height+15)/16; vblock++) {
for (int hblock=0; hblock<(width+15)/16; hblock++) {
jo_writeBits(&bits, 3, 2);
float Y[256], CBx[256], CRx[256];
for (int i=0; i<256; ++i) {
int y = vblock*16+(i/16);
int x = hblock*16+(i&15);
x = x >= width ? width-1 : x;
y = y >= height ? height-1 : y;
const unsigned char *c = rgbx + y*width*4+x*4;
float r = c[0], g = c[1], b = c[2];
Y[i] = (0.59f*r + 0.30f*g + 0.11f*b) * (219.f/255) + 16;
CBx[i] = (-0.17f*r - 0.33f*g + 0.50f*b) * (224.f/255) + 128;
CRx[i] = (0.50f*r - 0.42f*g - 0.08f*b) * (224.f/255) + 128;
}
// Downsample Cb,Cr (420 format)
float CB[64], CR[64];
for (int i=0; i<64; ++i) {
int j =(i&7)*2 + (i&56)*4;
CB[i] = (CBx[j] + CBx[j+1] + CBx[j+16] + CBx[j+17]) * 0.25f;
CR[i] = (CRx[j] + CRx[j+1] + CRx[j+16] + CRx[j+17]) * 0.25f;
}
for (int k1=0; k1<2; ++k1) {
for (int k2=0; k2<2; ++k2) {
float block[64];
for (int i=0; i<64; i+=8) {
int j = (i&7)+(i&56)*2 + k1*8*16 + k2*8;
memcpy(block+i, Y+j, 8*sizeof(Y[0]));
}
lastDCY = jo_processDU(&bits, block, s_jo_HTDC_Y, lastDCY);
}
}
lastDCCB = jo_processDU(&bits, CB, s_jo_HTDC_C, lastDCCB);
lastDCCR = jo_processDU(&bits, CR, s_jo_HTDC_C, lastDCCR);
}
}
jo_writeBits(&bits, 0, 7);
fwrite("\x00\x00\x01\xb7", 4, 1, fp); // End of Sequence
}
#endif
Results #
I encoded a couple of seconds from Big Buck Bunny as a sample: sample.mpeg
Thanks to jsmpeg we can see the output directly in the browser, after muxing it into an MPEG-TS container.
Quality is hardcoded and results in roughly 8mbps at a resolution of 684x385. The encoder performs only intra-frame compression, no inter-frame compression, so in its current state it’s more of a image encoder than a video encoder, as it just appends I-frames. Quality measurements are at roughly 27db PSNR and 0.9 SSIM. These values showcase the advanced age of MPEG-1…
Code changes #
Unfortunately, the output has increased saturation and contrast. This is due to RGB -> YCbCr conversion in line 230 - 232 scaling the final color vectors scaled too much. I fixed this by reverting the color space math changes that happened with the update to v1.02.
I’m not sure why the code change credited to r- lyeh happened, but I guess the used video player handled color space incorrectly. Both VLC and MPV playback the colors correctly with v1.03.