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decode_with_drops.c

# Decode With Drops Example

This is an example utility which drops a series of frames, as specified on the command line. This is useful for observing the error recovery features of the codec.

## Usage

This example adds a single argument to the `simple_decoder` example, which specifies the range or pattern of frames to drop. The parameter is parsed as follows:

    if(argc!=4)
        die("Usage: %s <infile> <outfile> <N-M|N/M>\n", argv[0]);
    {
        char *nptr;
        n = strtol(argv[3], &nptr, 0);
        m = strtol(nptr+1, NULL, 0);
        is_range = *nptr == '-';
        if(!n || !m || (*nptr != '-' && *nptr != '/'))
            die("Couldn't parse pattern %s\n", argv[3]);
    }

## Dropping A Range Of Frames

To drop a range of frames, specify the starting frame and the ending frame to drop, separated by a dash. The following command will drop frames 5 through 10 (base 1).

$ ./decode_with_drops in.ivf out.i420 5-10

## Dropping A Pattern Of Frames

To drop a pattern of frames, specify the number of frames to drop and the number of frames after which to repeat the pattern, separated by a forward-slash. The following command will drop 3 of 7 frames. Specifically, it will decode 4 frames, then drop 3 frames, and then repeat.

$ ./decode_with_drops in.ivf out.i420 3/7

## Extra Variables

This example maintains the pattern passed on the command line in the `n`, `m`, and `is_range` variables:

    int              n, m, is_range;

## Making The Drop Decision

The example decides whether to drop the frame based on the current frame number, immediately before decoding the frame.

    if((is_range && frame_cnt >= n && frame_cnt <= m)
       ||(!is_range && m - (frame_cnt-1)%m <= n)) {
       putc('X', stdout);
       continue;
    }
    putc('.', stdout);
    fflush(stdout);

# 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 utility which drops a series of frames, as specified
       on the command line. This is useful for observing the error recovery
       features of the codec.
     */
    #include <stdarg.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #define VPX_CODEC_DISABLE_COMPAT 1
    #include "./vpx_config.h"
    #include "vpx/vp8dx.h"
    #include "vpx/vpx_decoder.h"
    #define interface (vpx_codec_vp8_dx())

    #define IVF_FILE_HDR_SZ  (32)
    #define IVF_FRAME_HDR_SZ (12)

    static unsigned int mem_get_le32(const unsigned char *mem) {
        return (mem[3] << 24)|(mem[2] << 16)|(mem[1] << 8)|(mem[0]);
    }

    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);
    }

    int main(int argc, char **argv) {
        FILE            *infile, *outfile;
        vpx_codec_ctx_t  codec;
        int              flags = 0, frame_cnt = 0;
        unsigned char    file_hdr[IVF_FILE_HDR_SZ];
        unsigned char    frame_hdr[IVF_FRAME_HDR_SZ];
        unsigned char    frame[256*1024];
        vpx_codec_err_t  res;
        int              n, m, is_range;                                          //

        (void)res;
        /* Open files */
        if(argc!=4)                                                               //
            die("Usage: %s <infile> <outfile> <N-M|N/M>\n", argv[0]);             //
        {                                                                         //
            char *nptr;                                                           //
            n = strtol(argv[3], &nptr, 0);                                        //
            m = strtol(nptr+1, NULL, 0);                                          //
            is_range = *nptr == '-';                                              //
            if(!n || !m || (*nptr != '-' && *nptr != '/'))                        //
                die("Couldn't parse pattern %s\n", argv[3]);                      //
        }                                                                         //
        if(!(infile = fopen(argv[1], "rb")))
            die("Failed to open %s for reading", argv[1]);
        if(!(outfile = fopen(argv[2], "wb")))
            die("Failed to open %s for writing", argv[2]);

        /* Read file header */
        if(!(fread(file_hdr, 1, IVF_FILE_HDR_SZ, infile) == IVF_FILE_HDR_SZ
             && file_hdr[0]=='D' && file_hdr[1]=='K' && file_hdr[2]=='I'
             && file_hdr[3]=='F'))
            die("%s is not an IVF file.", argv[1]);

        printf("Using %s\n",vpx_codec_iface_name(interface));
        /* Initialize codec */
        if(vpx_codec_dec_init(&codec, interface, NULL, flags))
            die_codec(&codec, "Failed to initialize decoder");

        /* Read each frame */
        while(fread(frame_hdr, 1, IVF_FRAME_HDR_SZ, infile) == IVF_FRAME_HDR_SZ) {
            int               frame_sz = mem_get_le32(frame_hdr);
            vpx_codec_iter_t  iter = NULL;
            vpx_image_t      *img;

            frame_cnt++;
            if(frame_sz > sizeof(frame))
                die("Frame %d data too big for example code buffer", frame_sz);
            if(fread(frame, 1, frame_sz, infile) != frame_sz)
                die("Frame %d failed to read complete frame", frame_cnt);

            if((is_range && frame_cnt >= n && frame_cnt <= m)                     //
               ||(!is_range && m - (frame_cnt-1)%m <= n)) {                       //
               putc('X', stdout);                                                 //
               continue;                                                          //
            }                                                                     //
            putc('.', stdout);                                                    //
            fflush(stdout);                                                       //
            /* Decode the frame */
            if(vpx_codec_decode(&codec, frame, frame_sz, NULL, 0))
                die_codec(&codec, "Failed to decode frame");

            /* Write decoded data to disk */
            while((img = vpx_codec_get_frame(&codec, &iter))) {
                unsigned int plane, y;

                for(plane=0; plane < 3; plane++) {
                    unsigned char *buf =img->planes[plane];

                    for(y=0; y < (plane ? (img->d_h + 1) >> 1 : img->d_h); y++) {
                        (void) fwrite(buf, 1, (plane ? (img->d_w + 1) >> 1 : img->d_w),
                                      outfile);
                        buf += img->stride[plane];
                    }
                }
            }
        }
        printf("Processed %d frames.\n",frame_cnt);
        if(vpx_codec_destroy(&codec))
            die_codec(&codec, "Failed to destroy codec");

        fclose(outfile);
        fclose(infile);
        return EXIT_SUCCESS;
    }