AV1代码学习：解码端aomdec.c的main函数

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
1. 通过read_frame从码流中读取一帧数据
2. 调用aom_codec_decode解码当前帧
3. 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_IOstruct WebmInputContext webm_ctx;memset(&webm_ctx, 0, sizeof(webm_ctx));input.webm_ctx = &webm_ctx;
#endifstruct 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_MULTITHREADif (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;}
#endifinput.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_IOelse if (file_is_webm(input.webm_ctx, input.aom_input_ctx))input.aom_input_ctx->file_type = FILE_TYPE_WEBM;
#endifelse 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_IOfprintf(stderr, "aomdec was built without WebM container support.\n");
#endiffree(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);elseoutfile = 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_IOif (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));elseinterface = 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_LIBYUVlibyuv_scale(img, scaled_img, kFilterBox);img = scaled_img;
#elsefprintf(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 necessaryif (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 headerlen = 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 headerlen = 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 decodedif (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 { //！singleFilegenerate_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 fileif (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_IOif (input.aom_input_ctx->file_type == FILE_TYPE_WEBM)webm_free(input.webm_ctx);
#endifif (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;
}

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