WebM VP8 Codec SDK

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force_keyframe.c

# Forcing A Keyframe

This is an example demonstrating how to control placement of keyframes on a frame-by-frame basis.

## Configuration

Keyframes can be forced by setting the VPX_EFLAG_FORCE_KF bit of the flags passed to `vpx_codec_control()`. In this example, we force a keyframe every 8 frames.

    if(!(frame_cnt & 7))
        flags |= VPX_EFLAG_FORCE_KF;
    else
        flags &= ~VPX_EFLAG_FORCE_KF;

## Observing The Effects

The output of the encoder examples shows a ‘K’ rather than a dot ‘.’ when the encoder generates a keyframe. Note that every 8 frames a ‘K’ is output.

# 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 control placement of keyframes
       on a frame-by-frame basis.
     */
    #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;

        /* Open files */
        if(argc!=5)
            die("Usage: %s <width> <height> <infile> <outfile>\n", argv[0]);
        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;

                if(!(frame_cnt & 7))                                              //
                    flags |= VPX_EFLAG_FORCE_KF;                                  //
                else                                                              //
                    flags &= ~VPX_EFLAG_FORCE_KF;                                 //
                frame_avail = read_frame(infile, &raw);
                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;
    }