In the aom2.0 project, aomdec.c is the decoding end project, which mainly completes the analysis of the code stream and outputs the decoded YUV. Its entrance is the main function in amdec.c
The work done in the main function is very simple. First, the command line parameter loops is parsed, and the number of times the file is decoded is obtained, and then it starts to enter the decoding loop main_loop function
The code is as follows:
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;
}The main_loop function, the main process is as follows:
- Initialization variables, mainly including the context of some decoders, the number of read frames, decoding time, etc.
- Parse command line parameters
- Open the input file, determine the input file type (IVF/OBU/WEBM/RAW), and open the output yuv file
- Decoder type check
- Enter the decoding loop
- Read a frame of data from the code stream through read_frame
- Call aom_codec_decode to decode the current frame
- Call aom_codec_get_frame to get the data after decoding one frame, and then output the frame (you can zoom the current frame if necessary)
- Release variable
The code and comments are as follows:
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;
}