WebM VP8 Codec SDK
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This is an example of a simple decoder loop. It takes an input file containing the compressed data (in IVF format), passes it through the decoder, and writes the decompressed frames to disk. Other decoder examples build upon this one.
The details of the IVF format have been elided from this example for simplicity of presentation, as IVF files will not generally be used by your application. In general, an IVF file consists of a file header, followed by a variable number of frames. Each frame consists of a frame header followed by a variable length payload. The length of the payload is specified in the first four bytes of the frame header. The payload is the raw compressed data.
For decoders, you only have to include vpx_decoder.h
and then any
header files for the specific codecs you use. In this case, we’re using
vp8. The VPX_CODEC_DISABLE_COMPAT
macro can be defined to ensure
strict compliance with the latest SDK by disabling some backwards
compatibility features. Defining this macro is encouraged.
#define VPX_CODEC_DISABLE_COMPAT 1 #include "vpx/vpx_decoder.h" #include "vpx/vp8dx.h" #define interface (vpx_codec_vp8_dx())
The decoder is initialized by the following code. This is an example for
the VP8 decoder, but the code is analogous for all algorithms. Replace
vpx_codec_vp8_dx()
with a pointer to the interface exposed by the
algorithm you want to use. The cfg
argument is left as NULL in this
example, because we want the algorithm to determine the stream
configuration (width/height) and allocate memory automatically. This
parameter is generally only used if you need to preallocate memory,
particularly in External Memory Allocation mode.
/* Initialize codec */ if(vpx_codec_dec_init(&codec, interface, NULL, flags)) die_codec(&codec, "Failed to initialize decoder");
Once the frame has been read into memory, it is decoded using the
vpx_codec_decode
function. The call takes a pointer to the data
(frame
) and the length of the data (frame_sz
). No application data
is associated with the frame in this example, so the user_priv
parameter is NULL. The deadline
parameter is left at zero for this
example. This parameter is generally only used when doing adaptive
postprocessing.
/* Decode the frame */ if(vpx_codec_decode(&codec, frame, frame_sz, NULL, 0)) die_codec(&codec, "Failed to decode frame");
Codecs may produce a variable number of output frames for every call to
vpx_codec_decode
. These frames are retrieved by the
vpx_codec_get_frame
iterator function. The iterator variable iter
is
initialized to NULL each time vpx_codec_decode
is called.
vpx_codec_get_frame
is called in a loop, returning a pointer to a
decoded image or NULL to indicate the end of list.
while((img = vpx_codec_get_frame(&codec, &iter))) {
In this example, we simply write the encoded data to disk. It is
important to honor the image’s stride
values.
for(plane=0; plane < 3; plane++) { unsigned char *buf =img->planes[plane]; for(y=0; y<img->d_h >> (plane?1:0); y++) { if(fwrite(buf, 1, img->d_w >> (plane?1:0), outfile)); buf += img->stride[plane]; } }
The vpx_codec_destroy
call frees any memory allocated by the codec.
if(vpx_codec_destroy(&codec)) die_codec(&codec, "Failed to destroy codec");
This example does not special case any error return codes. If there was
an error, a descriptive message is printed and the program exits. With
few exeptions, vpx_codec functions return an enumerated error status,
with the value 0
indicating success.
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); }
/* 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 of a simple decoder loop. It takes an input file containing the compressed data (in IVF format), passes it through the decoder, and writes the decompressed frames to disk. Other decoder examples build upon this one. The details of the IVF format have been elided from this example for simplicity of presentation, as IVF files will not generally be used by your application. In general, an IVF file consists of a file header, followed by a variable number of frames. Each frame consists of a frame header followed by a variable length payload. The length of the payload is specified in the first four bytes of the frame header. The payload is the raw compressed data. */ #include <stdio.h> #include <stdlib.h> #include <stdarg.h> #include <string.h> #define VPX_CODEC_DISABLE_COMPAT 1 #include "vpx/vpx_decoder.h" #include "vpx/vp8dx.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; (void)res; /* Open files */ if(argc!=3) die("Usage: %s <infile> <outfile>\n", argv[0]); 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); /* 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<img->d_h >> (plane?1:0); y++) { // if(fwrite(buf, 1, img->d_w >> (plane?1:0), 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; }