aom2.0的工程中，aomdec.c是解码端工程，主要完成码流的解析，并输出解码后的YUV，其入口是amdec.c中的main函数
在main函数里面做的工作很简单，首先解析了命令行参数loops，获取其解码文件的次数，然后开始进入解码循环main_loop函数中
其代码如下：
int main(int argc, const char **argv_) {
unsigned int loops = 1, i;
char **argv, **argi, **argj;
struct arg arg;
int error = 0;
argv = argv_dup(argc - 1, argv_ + 1);
for (argi = argj = argv; (*argj = *argi); argi += arg.argv_step) {
memset(&arg, 0, sizeof(arg));
arg.argv_step = 1;
if (arg_match(&arg, &looparg, argi)) {
loops = arg_parse_uint(&arg);
break;
}
}
free(argv);
for (i = 0; !error && i < loops; i++) error = main_loop(argc, argv_);
return error;
}main_loop函数，主要流程如下：
- 初始化变量， 主要包括一些解码器的上下文、读取帧数、解码时间等
- 解析命令行参数
- 打开输入文件，判断输入文件类型（IVF/OBU/WEBM/RAW），打开输出的yuv文件
- 解码器类型检查
- 进入解码循环
- 通过read_frame从码流中读取一帧数据
- 调用aom_codec_decode解码当前帧
- 调用aom_codec_get_frame获得解码一帧后的数据，然后输出该帧（如果需要可以对当前帧进行缩放）
- 释放变量
代码及注释如下：
static int main_loop(int argc, const char **argv_) {
aom_codec_ctx_t decoder;
char *fn = NULL;
int i;
int ret = EXIT_FAILURE;
uint8_t *buf = NULL;
size_t bytes_in_buffer = 0, buffer_size = 0;
FILE *infile;
int frame_in = 0, frame_out = 0, flipuv = 0, noblit = 0;
int do_md5 = 0, progress = 0;
int stop_after = 0, summary = 0, quiet = 1;
int arg_skip = 0;
int keep_going = 0;
uint64_t dx_time = 0;
struct arg arg;
char **argv, **argi, **argj;
int single_file;
int use_y4m = 1;
int opt_yv12 = 0;
int opt_i420 = 0;
int opt_raw = 0;
aom_codec_dec_cfg_t cfg = { 0, 0, 0, !FORCE_HIGHBITDEPTH_DECODING };
unsigned int fixed_output_bit_depth = 0;
unsigned int is_annexb = 0;
int frames_corrupted = 0;
int dec_flags = 0;
int do_scale = 0;
int operating_point = 0;
int output_all_layers = 0;
int skip_film_grain = 0;
int enable_row_mt = 0;
aom_image_t *scaled_img = NULL;
aom_image_t *img_shifted = NULL;
int frame_avail, got_data, flush_decoder = 0;
int num_external_frame_buffers = 0;
struct ExternalFrameBufferList ext_fb_list = { 0, NULL };
const char *outfile_pattern = NULL;
char outfile_name[PATH_MAX] = { 0 };
FILE *outfile = NULL;
FILE *framestats_file = NULL;
MD5Context md5_ctx;
unsigned char md5_digest[16];
struct AvxDecInputContext input = { NULL, NULL, NULL };
struct AvxInputContext aom_input_ctx;
memset(&aom_input_ctx, 0, sizeof(aom_input_ctx));
#if CONFIG_WEBM_IO
struct WebmInputContext webm_ctx;
memset(&webm_ctx, 0, sizeof(webm_ctx));
input.webm_ctx = &webm_ctx;
#endif
struct ObuDecInputContext obu_ctx = { NULL, NULL, 0, 0, 0 };
int is_ivf = 0;
obu_ctx.avx_ctx = &aom_input_ctx;
input.obu_ctx = &obu_ctx;
input.aom_input_ctx = &aom_input_ctx;
/* Parse command line */
exec_name = argv_[0];
argv = argv_dup(argc - 1, argv_ + 1);
aom_codec_iface_t *interface = NULL;
for (argi = argj = argv; (*argj = *argi); argi += arg.argv_step) {
memset(&arg, 0, sizeof(arg));
arg.argv_step = 1;
if (arg_match(&arg, &help, argi)) {
show_help(stdout, 0);
exit(EXIT_SUCCESS);
} else if (arg_match(&arg, &codecarg, argi)) {
interface = get_aom_decoder_by_short_name(arg.val);
if (!interface)
die("Error: Unrecognized argument (%s) to --codec\n", arg.val);
} else if (arg_match(&arg, &looparg, argi)) {
// no-op
} else if (arg_match(&arg, &outputfile, argi)) { //输出文件类型
outfile_pattern = arg.val;
} else if (arg_match(&arg, &use_yv12, argi)) {
use_y4m = 0;
flipuv = 1;
opt_yv12 = 1;
opt_i420 = 0;
opt_raw = 0;
} else if (arg_match(&arg, &use_i420, argi)) {
use_y4m = 0;
flipuv = 0;
opt_yv12 = 0;
opt_i420 = 1;
opt_raw = 0;
} else if (arg_match(&arg, &rawvideo, argi)) {
use_y4m = 0;
opt_yv12 = 0;
opt_i420 = 0;
opt_raw = 1;
} else if (arg_match(&arg, &flipuvarg, argi)) {
flipuv = 1;
} else if (arg_match(&arg, &noblitarg, argi)) {
noblit = 1;
} else if (arg_match(&arg, &progressarg, argi)) {
progress = 1;
} else if (arg_match(&arg, &limitarg, argi)) {
stop_after = arg_parse_uint(&arg);
} else if (arg_match(&arg, &skiparg, argi)) {
arg_skip = arg_parse_uint(&arg);
} else if (arg_match(&arg, &md5arg, argi)) {
do_md5 = 1;
} else if (arg_match(&arg, &framestatsarg, argi)) {
framestats_file = fopen(arg.val, "w");
if (!framestats_file) {
die("Error: Could not open --framestats file (%s) for writing.\n",
arg.val);
}
} else if (arg_match(&arg, &summaryarg, argi)) {
summary = 1;
} else if (arg_match(&arg, &threadsarg, argi)) {
cfg.threads = arg_parse_uint(&arg);
#if !CONFIG_MULTITHREAD
if (cfg.threads > 1) {
die("Error: --threads=%d is not supported when CONFIG_MULTITHREAD = "
"0.\n",
cfg.threads);
}
#endif
} else if (arg_match(&arg, &rowmtarg, argi)) {
enable_row_mt = arg_parse_uint(&arg);
} else if (arg_match(&arg, &verbosearg, argi)) {
quiet = 0;
} else if (arg_match(&arg, &scalearg, argi)) {
do_scale = 1;
} else if (arg_match(&arg, &fb_arg, argi)) {
num_external_frame_buffers = arg_parse_uint(&arg);
} else if (arg_match(&arg, &continuearg, argi)) {
keep_going = 1;
} else if (arg_match(&arg, &outbitdeptharg, argi)) {
fixed_output_bit_depth = arg_parse_uint(&arg);
} else if (arg_match(&arg, &isannexb, argi)) {
is_annexb = 1;
input.obu_ctx->is_annexb = 1;
} else if (arg_match(&arg, &oppointarg, argi)) {
operating_point = arg_parse_int(&arg);
} else if (arg_match(&arg, &outallarg, argi)) {
output_all_layers = 1;
} else if (arg_match(&arg, &skipfilmgrain, argi)) {
skip_film_grain = 1;
} else {
argj++;
}
}
/* Check for unrecognized options */
for (argi = argv; *argi; argi++)
if (argi[0][0] == '-' && strlen(argi[0]) > 1)
die("Error: Unrecognized option %s\n", *argi);
/* Handle non-option arguments */
fn = argv[0];
if (!fn) {
free(argv);
fprintf(stderr, "No input file specified!\n");
usage_exit();
}
/* Open file */
infile = strcmp(fn, "-") ? fopen(fn, "rb") : set_binary_mode(stdin);
if (!infile) {
fatal("Failed to open input file '%s'", strcmp(fn, "-") ? fn : "stdin");
}
#if CONFIG_OS_SUPPORT
/* Make sure we don't dump to the terminal, unless forced to with -o - */
if (!outfile_pattern && isatty(STDOUT_FILENO) && !do_md5 && !noblit) {
fprintf(stderr,
"Not dumping raw video to your terminal. Use '-o -' to "
"override.\n");
free(argv);
return EXIT_FAILURE;
}
#endif
input.aom_input_ctx->filename = fn;
input.aom_input_ctx->file = infile;
// 判断输入文件类型
if (file_is_ivf(input.aom_input_ctx)) {
input.aom_input_ctx->file_type = FILE_TYPE_IVF;
is_ivf = 1;
}
#if CONFIG_WEBM_IO
else if (file_is_webm(input.webm_ctx, input.aom_input_ctx))
input.aom_input_ctx->file_type = FILE_TYPE_WEBM;
#endif
else if (file_is_obu(&obu_ctx))
input.aom_input_ctx->file_type = FILE_TYPE_OBU;
else if (file_is_raw(input.aom_input_ctx))
input.aom_input_ctx->file_type = FILE_TYPE_RAW;
else {
fprintf(stderr, "Unrecognized input file type.\n");
#if !CONFIG_WEBM_IO
fprintf(stderr, "aomdec was built without WebM container support.\n");
#endif
free(argv);
return EXIT_FAILURE;
}
outfile_pattern = outfile_pattern ? outfile_pattern : "-";
single_file = is_single_file(outfile_pattern);
if (!noblit && single_file) {
generate_filename(outfile_pattern, outfile_name, PATH_MAX,
aom_input_ctx.width, aom_input_ctx.height, 0);
if (do_md5)
MD5Init(&md5_ctx);
else
outfile = open_outfile(outfile_name);
}
if (use_y4m && !noblit) {
if (!single_file) {
fprintf(stderr,
"YUV4MPEG2 not supported with output patterns,"
" try --i420 or --yv12 or --rawvideo.\n");
return EXIT_FAILURE;
}
#if CONFIG_WEBM_IO
if (aom_input_ctx.file_type == FILE_TYPE_WEBM) {
if (webm_guess_framerate(input.webm_ctx, input.aom_input_ctx)) {
fprintf(stderr,
"Failed to guess framerate -- error parsing "
"webm file?\n");
return EXIT_FAILURE;
}
}
#endif
}
aom_codec_iface_t *fourcc_interface =
get_aom_decoder_by_fourcc(aom_input_ctx.fourcc);
if (is_ivf && !fourcc_interface)
fatal("Unsupported fourcc: %x\n", aom_input_ctx.fourcc);
if (interface && fourcc_interface && interface != fourcc_interface)
warn("Header indicates codec: %s\n",
aom_codec_iface_name(fourcc_interface));
else
interface = fourcc_interface;
if (!interface) interface = get_aom_decoder_by_index(0);
dec_flags = 0;
if (aom_codec_dec_init(&decoder, interface, &cfg, dec_flags)) {
fprintf(stderr, "Failed to initialize decoder: %s\n",
aom_codec_error(&decoder));
goto fail2;
}
if (!quiet) fprintf(stderr, "%s\n", decoder.name);
if (AOM_CODEC_CONTROL_TYPECHECKED(&decoder, AV1D_SET_IS_ANNEXB, is_annexb)) {
fprintf(stderr, "Failed to set is_annexb: %s\n", aom_codec_error(&decoder));
goto fail;
}
if (AOM_CODEC_CONTROL_TYPECHECKED(&decoder, AV1D_SET_OPERATING_POINT,
operating_point)) {
fprintf(stderr, "Failed to set operating_point: %s\n",
aom_codec_error(&decoder));
goto fail;
}
if (AOM_CODEC_CONTROL_TYPECHECKED(&decoder, AV1D_SET_OUTPUT_ALL_LAYERS,
output_all_layers)) {
fprintf(stderr, "Failed to set output_all_layers: %s\n",
aom_codec_error(&decoder));
goto fail;
}
if (AOM_CODEC_CONTROL_TYPECHECKED(&decoder, AV1D_SET_SKIP_FILM_GRAIN,
skip_film_grain)) {
fprintf(stderr, "Failed to set skip_film_grain: %s\n",
aom_codec_error(&decoder));
goto fail;
}
if (AOM_CODEC_CONTROL_TYPECHECKED(&decoder, AV1D_SET_ROW_MT, enable_row_mt)) {
fprintf(stderr, "Failed to set row multithreading mode: %s\n",
aom_codec_error(&decoder));
goto fail;
}
// 跳过前几个帧
if (arg_skip) fprintf(stderr, "Skipping first %d frames.\n", arg_skip);
while (arg_skip) {
if (read_frame(&input, &buf, &bytes_in_buffer, &buffer_size)) break;
arg_skip--;
}
if (num_external_frame_buffers > 0) {
ext_fb_list.num_external_frame_buffers = num_external_frame_buffers;
ext_fb_list.ext_fb = (struct ExternalFrameBuffer *)calloc(
num_external_frame_buffers, sizeof(*ext_fb_list.ext_fb));
if (aom_codec_set_frame_buffer_functions(&decoder, get_av1_frame_buffer,
release_av1_frame_buffer,
&ext_fb_list)) {
fprintf(stderr, "Failed to configure external frame buffers: %s\n",
aom_codec_error(&decoder));
goto fail;
}
}
frame_avail = 1;
got_data = 0;
if (framestats_file) fprintf(framestats_file, "bytes,qp\r\n");
/* Decode file */
while (frame_avail || got_data) {
aom_codec_iter_t iter = NULL;
aom_image_t *img;
struct aom_usec_timer timer;
int corrupted = 0;
frame_avail = 0;
if (!stop_after || frame_in < stop_after) {
if (!read_frame(&input, &buf, &bytes_in_buffer, &buffer_size)) { //从码流中读取一帧数据
frame_avail = 1;
frame_in++;
aom_usec_timer_start(&timer);//计时器开始
if (aom_codec_decode(&decoder, buf, bytes_in_buffer, NULL)) { //进行解码
const char *detail = aom_codec_error_detail(&decoder);
warn("Failed to decode frame %d: %s", frame_in,
aom_codec_error(&decoder));
if (detail) warn("Additional information: %s", detail);
if (!keep_going) goto fail;
}
if (framestats_file) { //打印解码时的数据
int qp;
if (AOM_CODEC_CONTROL_TYPECHECKED(&decoder, AOMD_GET_LAST_QUANTIZER,
&qp)) {
warn("Failed AOMD_GET_LAST_QUANTIZER: %s",
aom_codec_error(&decoder));
if (!keep_going) goto fail;
}
fprintf(framestats_file, "%d,%d\r\n", (int)bytes_in_buffer, qp);
}
aom_usec_timer_mark(&timer);
dx_time += aom_usec_timer_elapsed(&timer);//累计解码时间
} else {
flush_decoder = 1;//如果没有读取到数据就刷新解码器
}
} else {
flush_decoder = 1;//停止读取帧数据，刷新解码器
}
aom_usec_timer_start(&timer);
if (flush_decoder) {
// Flush the decoder. 刷新解码器
if (aom_codec_decode(&decoder, NULL, 0, NULL)) {
warn("Failed to flush decoder: %s", aom_codec_error(&decoder));
}
}
aom_usec_timer_mark(&timer);
dx_time += aom_usec_timer_elapsed(&timer);
got_data = 0;
while ((img = aom_codec_get_frame(&decoder, &iter))) {
++frame_out;
got_data = 1;
if (AOM_CODEC_CONTROL_TYPECHECKED(&decoder, AOMD_GET_FRAME_CORRUPTED,
&corrupted)) { //检查帧是否损坏
warn("Failed AOM_GET_FRAME_CORRUPTED: %s", aom_codec_error(&decoder));
if (!keep_going) goto fail;
}
frames_corrupted += corrupted;
if (progress) show_progress(frame_in, frame_out, dx_time); //打印每一帧的解码信息
if (!noblit) { //如果对解码帧进行处理
const int PLANES_YUV[] = { AOM_PLANE_Y, AOM_PLANE_U, AOM_PLANE_V };
const int PLANES_YVU[] = { AOM_PLANE_Y, AOM_PLANE_V, AOM_PLANE_U };
const int *planes = flipuv ? PLANES_YVU : PLANES_YUV;
if (do_scale) { //如果需要输出帧进行缩放
if (frame_out == 1) {
// If the output frames are to be scaled to a fixed display size
// then use the width and height specified in the container. If
// either of these is set to 0, use the display size set in the
// first frame header. If that is unavailable, use the raw decoded
// size of the first decoded frame.
// 如果要将输出帧缩放为固定的显示大小，则使用容器中指定的宽度和高度。
// 如果其中任何一个设置为0，则使用在第一个帧标题中设置的显示大小。
// 如果不可用，则使用第一个解码帧的原始解码大小。
int render_width = aom_input_ctx.width;
int render_height = aom_input_ctx.height;
if (!render_width || !render_height) {
int render_size[2];
if (AOM_CODEC_CONTROL_TYPECHECKED(&decoder, AV1D_GET_DISPLAY_SIZE,
render_size)) {
// As last resort use size of first frame as display size.
render_width = img->d_w;
render_height = img->d_h;
} else {
render_width = render_size[0];
render_height = render_size[1];
}
}
scaled_img =
aom_img_alloc(NULL, img->fmt, render_width, render_height, 16);
scaled_img->bit_depth = img->bit_depth;
scaled_img->monochrome = img->monochrome;
scaled_img->csp = img->csp;
}
if (img->d_w != scaled_img->d_w || img->d_h != scaled_img->d_h) {
#if CONFIG_LIBYUV
libyuv_scale(img, scaled_img, kFilterBox);
img = scaled_img;
#else
fprintf(
stderr,
"Failed to scale output frame: %s.\n"
"libyuv is required for scaling but is currently disabled.\n"
"Be sure to specify -DCONFIG_LIBYUV=1 when running cmake.\n",
aom_codec_error(&decoder));
goto fail;
#endif
}
}
// Default to codec bit depth if output bit depth not set
// 如果未设置输出位深度，则默认为编解码器位深度
unsigned int output_bit_depth;
if (!fixed_output_bit_depth && single_file) {
output_bit_depth = img->bit_depth;
} else {
output_bit_depth = fixed_output_bit_depth;
}
// Shift up or down if necessary
if (output_bit_depth != 0)
aom_shift_img(output_bit_depth, &img, &img_shifted);
aom_input_ctx.width = img->d_w;
aom_input_ctx.height = img->d_h;
int num_planes = (opt_raw && img->monochrome) ? 1 : 3;
if (single_file) {
if (use_y4m) { //如果输出y4m格式的视频
char y4m_buf[Y4M_BUFFER_SIZE] = { 0 };
size_t len = 0;
if (frame_out == 1) {
// Y4M file header
len = y4m_write_file_header(
y4m_buf, sizeof(y4m_buf), aom_input_ctx.width,
aom_input_ctx.height, &aom_input_ctx.framerate,
img->monochrome, img->csp, img->fmt, img->bit_depth);
if (img->csp == AOM_CSP_COLOCATED) {
fprintf(stderr,
"Warning: Y4M lacks a colorspace for colocated "
"chroma. Using a placeholder.\n");
}
if (do_md5) {
MD5Update(&md5_ctx, (md5byte *)y4m_buf, (unsigned int)len);
} else {
fputs(y4m_buf, outfile);
}
}
// Y4M frame header
len = y4m_write_frame_header(y4m_buf, sizeof(y4m_buf));
if (do_md5) {
MD5Update(&md5_ctx, (md5byte *)y4m_buf, (unsigned int)len);
y4m_update_image_md5(img, planes, &md5_ctx);
} else {
fputs(y4m_buf, outfile);
y4m_write_image_file(img, planes, outfile);
}
} else { //输出原始YUV视频
if (frame_out == 1) {
// Check if --yv12 or --i420 options are consistent with the
// bit-stream decoded
if (opt_i420) {
if (img->fmt != AOM_IMG_FMT_I420 &&
img->fmt != AOM_IMG_FMT_I42016) {
fprintf(stderr,
"Cannot produce i420 output for bit-stream.\n");
goto fail;
}
}
if (opt_yv12) {
if ((img->fmt != AOM_IMG_FMT_I420 &&
img->fmt != AOM_IMG_FMT_YV12) ||
img->bit_depth != 8) {
fprintf(stderr,
"Cannot produce yv12 output for bit-stream.\n");
goto fail;
}
}
}
if (do_md5) {
raw_update_image_md5(img, planes, num_planes, &md5_ctx);
} else {
raw_write_image_file(img, planes, num_planes, outfile);
}
}
} else { //！singleFile
generate_filename(outfile_pattern, outfile_name, PATH_MAX, img->d_w,
img->d_h, frame_in);
if (do_md5) {
MD5Init(&md5_ctx);
if (use_y4m) {
y4m_update_image_md5(img, planes, &md5_ctx);
} else {
raw_update_image_md5(img, planes, num_planes, &md5_ctx);
}
MD5Final(md5_digest, &md5_ctx);
print_md5(md5_digest, outfile_name);
} else {
outfile = open_outfile(outfile_name);
if (use_y4m) {
y4m_write_image_file(img, planes, outfile);
} else {
raw_write_image_file(img, planes, num_planes, outfile);
}
fclose(outfile);
}
}
}
}// 解码帧
}// Decode file
if (summary || progress) {
show_progress(frame_in, frame_out, dx_time);
fprintf(stderr, "\n");
}
if (frames_corrupted) {
fprintf(stderr, "WARNING: %d frames corrupted.\n", frames_corrupted);
} else {
ret = EXIT_SUCCESS;
}
fail:
if (aom_codec_destroy(&decoder)) {
fprintf(stderr, "Failed to destroy decoder: %s\n",
aom_codec_error(&decoder));
}
fail2:
if (!noblit && single_file) {
if (do_md5) {
MD5Final(md5_digest, &md5_ctx);
print_md5(md5_digest, outfile_name);
} else {
fclose(outfile);
}
}
#if CONFIG_WEBM_IO
if (input.aom_input_ctx->file_type == FILE_TYPE_WEBM)
webm_free(input.webm_ctx);
#endif
if (input.aom_input_ctx->file_type == FILE_TYPE_OBU)
obudec_free(input.obu_ctx);
if (input.aom_input_ctx->file_type != FILE_TYPE_WEBM) free(buf);
if (scaled_img) aom_img_free(scaled_img);
if (img_shifted) aom_img_free(img_shifted);
for (i = 0; i < ext_fb_list.num_external_frame_buffers; ++i) {
free(ext_fb_list.ext_fb[i].data);
}
free(ext_fb_list.ext_fb);
fclose(infile);
if (framestats_file) fclose(framestats_file);
free(argv);
return ret;
}