WebM VP8 Codec SDK
vp8cx_set_ref.c

VP8 Set Reference Frame

This is an example demonstrating how to overwrite the VP8 encoder’s internal reference frame. In the sample we set the last frame to the current frame. If this is done at a cut scene it will avoid a keyframe. This technique could be used to bounce between two cameras.

Note that the decoder would also have to set the reference frame to the same value on the same frame, or the video will become corrupt.

Usage

This example adds a single argument to the simple_encoder example, which specifies the frame number to update the reference frame on. The parameter is parsed as follows:

if(argc!=6)
    die("Usage: %s <width> <height> <infile> <outfile> <frame>\n",
        argv[0]);
 
    update_frame_num = atoi(argv[5]);
    if(!update_frame_num)
        die("Couldn't parse frame number '%s'\n", argv[5]);
 

Extra Variables

This example maintains the frame number passed on the command line in the update_frame_num variable:

int                  update_frame_num = 0;

Configuration

The reference frame is updated on the frame specified on the command line.

frame_avail = read_frame(infile, &raw);
 
if(frame_cnt + 1 == update_frame_num) {
    vpx_ref_frame_t ref;
 
    ref.frame_type = VP8_LAST_FRAME;
    ref.img        = raw;
 
    if(vpx_codec_control(&codec, VP8_SET_REFERENCE, &ref))
        die_codec(&codec, "Failed to set reference frame");
}
 
if(vpx_codec_encode(&codec, frame_avail? &raw : NULL, frame_cnt,
                    1, flags, VPX_DL_REALTIME))
    die_codec(&codec, "Failed to encode frame");

Observing The Effects

Use the simple_encoder example to encode a sample with a cut scene. Determine the frame number of the cut scene by looking for a generated key-frame (indicated by a ‘K’). Supply that frame number as an argument to this example, and observe that no key-frame is generated.

Putting It All Together

/*
    Copyright (c) 2010 The WebM project authors. All Rights Reserved.
  
    Use of this source code is governed by a BSD-style license
    that can be found in the LICENSE file in the root of the source
    tree. An additional intellectual property rights grant can be found
    in the file PATENTS.  All contributing project authors may
    be found in the AUTHORS file in the root of the source tree.
 */
 
 
/*
   This is an example demonstrating how to overwrite the VP8 encoder's
   internal reference frame. In the sample we set the last frame to the
   current frame. If this is done at a cut scene it will avoid a keyframe.
   This technique could be used to bounce between two cameras.
   
   Note that the decoder would also have to set the reference frame to the
   same value on the same frame, or the video will become corrupt.
 */
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
#define VPX_CODEC_DISABLE_COMPAT 1
#include "vpx/vpx_encoder.h"
#include "vpx/vp8cx.h"
#define interface (vpx_codec_vp8_cx())
#define fourcc    0x30385056
 
#define IVF_FILE_HDR_SZ  (32)
#define IVF_FRAME_HDR_SZ (12)
 
static void mem_put_le16(char *mem, unsigned int val) {
    mem[0] = val;
    mem[1] = val>>8;
}
 
static void mem_put_le32(char *mem, unsigned int val) {
    mem[0] = val;
    mem[1] = val>>8;
    mem[2] = val>>16;
    mem[3] = val>>24;
}
 
static void die(const char *fmt, ...) {
    va_list ap;
 
    va_start(ap, fmt);
    vprintf(fmt, ap);
    if(fmt[strlen(fmt)-1] != '\n')
        printf("\n");
    exit(EXIT_FAILURE);
}
 
static void die_codec(vpx_codec_ctx_t *ctx, const char *s) {
    const char *detail = vpx_codec_error_detail(ctx);
 
    printf("%s: %s\n", s, vpx_codec_error(ctx));
    if(detail)
        printf("    %s\n",detail);
    exit(EXIT_FAILURE);
}
 
static int read_frame(FILE *f, vpx_image_t *img) {
    size_t nbytes, to_read;
    int    res = 1;
 
    to_read = img->w*img->h*3/2;
    nbytes = fread(img->planes[0], 1, to_read, f);
    if(nbytes != to_read) {
        res = 0;
        if(nbytes > 0)
            printf("Warning: Read partial frame. Check your width & height!\n");
    }
    return res;
}
 
static void write_ivf_file_header(FILE *outfile,
                                  const vpx_codec_enc_cfg_t *cfg,
                                  int frame_cnt) {
    char header[32];
 
    if(cfg->g_pass != VPX_RC_ONE_PASS && cfg->g_pass != VPX_RC_LAST_PASS)
        return;
    header[0] = 'D';
    header[1] = 'K';
    header[2] = 'I';
    header[3] = 'F';
    mem_put_le16(header+4,  0);                   /* version */
    mem_put_le16(header+6,  32);                  /* headersize */
    mem_put_le32(header+8,  fourcc);              /* headersize */
    mem_put_le16(header+12, cfg->g_w);            /* width */
    mem_put_le16(header+14, cfg->g_h);            /* height */
    mem_put_le32(header+16, cfg->g_timebase.den); /* rate */
    mem_put_le32(header+20, cfg->g_timebase.num); /* scale */
    mem_put_le32(header+24, frame_cnt);           /* length */
    mem_put_le32(header+28, 0);                   /* unused */
 
    (void) fwrite(header, 1, 32, outfile);
}
 
 
static void write_ivf_frame_header(FILE *outfile,
                                   const vpx_codec_cx_pkt_t *pkt)
{
    char             header[12];
    vpx_codec_pts_t  pts;
 
    if(pkt->kind != VPX_CODEC_CX_FRAME_PKT)
        return;
 
    pts = pkt->data.frame.pts;
    mem_put_le32(header, pkt->data.frame.sz);
    mem_put_le32(header+4, pts&0xFFFFFFFF);
    mem_put_le32(header+8, pts >> 32);
 
    (void) fwrite(header, 1, 12, outfile);
}
 
int main(int argc, char **argv) {
    FILE                *infile, *outfile;
    vpx_codec_ctx_t      codec;
    vpx_codec_enc_cfg_t  cfg;
    int                  frame_cnt = 0;
    vpx_image_t          raw;
    vpx_codec_err_t      res;
    long                 width;
    long                 height;
    int                  frame_avail;
    int                  got_data;
    int                  flags = 0;
    int                  update_frame_num = 0;                                //
 
    /* Open files */
    if(argc!=6)                                                               //
        die("Usage: %s <width> <height> <infile> <outfile> <frame>\n",        //
            argv[0]);                                                         //
                                                                              //
        update_frame_num = atoi(argv[5]);                                     //
        if(!update_frame_num)                                                 //
            die("Couldn't parse frame number '%s'\n", argv[5]);               //
                                                                              //
    width = strtol(argv[1], NULL, 0);
    height = strtol(argv[2], NULL, 0);
    if(width < 16 || width%2 || height <16 || height%2)
        die("Invalid resolution: %ldx%ld", width, height);
    if(!vpx_img_alloc(&raw, VPX_IMG_FMT_I420, width, height, 1))
        die("Faile to allocate image", width, height);
    if(!(outfile = fopen(argv[4], "wb")))
        die("Failed to open %s for writing", argv[4]);
 
    printf("Using %s\n",vpx_codec_iface_name(interface));
 
    /* Populate encoder configuration */
    res = vpx_codec_enc_config_default(interface, &cfg, 0);
    if(res) {
        printf("Failed to get config: %s\n", vpx_codec_err_to_string(res));
        return EXIT_FAILURE;
    }
 
    /* Update the default configuration with our settings */
    cfg.rc_target_bitrate = width * height * cfg.rc_target_bitrate
                            / cfg.g_w / cfg.g_h;
    cfg.g_w = width;
    cfg.g_h = height;
 
    write_ivf_file_header(outfile, &cfg, 0);
 
 
        /* Open input file for this encoding pass */
        if(!(infile = fopen(argv[3], "rb")))
            die("Failed to open %s for reading", argv[3]);
 
        /* Initialize codec */
        if(vpx_codec_enc_init(&codec, interface, &cfg, 0))
            die_codec(&codec, "Failed to initialize encoder");
 
        frame_avail = 1;
        got_data = 0;
        while(frame_avail || got_data) {
            vpx_codec_iter_t iter = NULL;
            const vpx_codec_cx_pkt_t *pkt;
 
            frame_avail = read_frame(infile, &raw);                           //
                                                                              //
            if(frame_cnt + 1 == update_frame_num) {                           //
                vpx_ref_frame_t ref;                                          //
                                                                              //
                ref.frame_type = VP8_LAST_FRAME;                              //
                ref.img        = raw;                                         //
                                                                              //
                if(vpx_codec_control(&codec, VP8_SET_REFERENCE, &ref))        //
                    die_codec(&codec, "Failed to set reference frame");       //
            }                                                                 //
                                                                              //
            if(vpx_codec_encode(&codec, frame_avail? &raw : NULL, frame_cnt,  //
                                1, flags, VPX_DL_REALTIME))                   //
                die_codec(&codec, "Failed to encode frame");                  //
            got_data = 0;
            while( (pkt = vpx_codec_get_cx_data(&codec, &iter)) ) {
                got_data = 1;
                switch(pkt->kind) {
                case VPX_CODEC_CX_FRAME_PKT:
                    write_ivf_frame_header(outfile, pkt);
                    (void) fwrite(pkt->data.frame.buf, 1, pkt->data.frame.sz,
                                  outfile);
                    break;
                default:
                    break;
                }
                printf(pkt->kind == VPX_CODEC_CX_FRAME_PKT
                       && (pkt->data.frame.flags & VPX_FRAME_IS_KEY)? "K":".");
                fflush(stdout);
            }
            frame_cnt++;
        }
        printf("\n");
        fclose(infile);
 
    printf("Processed %d frames.\n",frame_cnt-1);
    vpx_img_free(&raw);
    if(vpx_codec_destroy(&codec))
        die_codec(&codec, "Failed to destroy codec");
 
    /* Try to rewrite the file header with the actual frame count */
    if(!fseek(outfile, 0, SEEK_SET))
        write_ivf_file_header(outfile, &cfg, frame_cnt-1);
    fclose(outfile);
    return EXIT_SUCCESS;
}