obs 源碼解析筆記

obs 源碼解析筆記

由於obs rtp音頻傳輸有問題，所以可能需要修改obs源碼，學習了兩天，發現官方文檔有些混亂，國內有關說明又少，特此記錄，也方便以後自己查閱。這裏主要涉及工作有關源碼其他基本略過，除非重要。
原文鏈接：https://blog.csdn.net/weixin_44259356/article/details/102582493

obs源碼編譯

見我的另一篇文章：VS2017-OBS24.03源碼編譯
https://blog.csdn.net/weixin_44259356/article/details/102548121

obs源碼簡介

obs有兩套源碼，新版源碼採用微內核思想，核心功能很少，大部分功能通過插件的方式實現，方便後續維護開發，這裏我用的是最新版源碼24.03。

插件模塊頭介紹

libobs / obs-module.h –用於創建插件模塊的主要標頭。該文件自動包括以下文件：
libobs / obs.h –主libobs標頭。該文件自動包括以下文件：
libobs / obs-source.h –用於在插件模塊中實現源代碼
libobs / obs-output.h –用於在插件模塊中實現輸出
libobs / obs-encoder.h –用於在插件模塊中實現編碼器
libobs / obs-service.h –用於在插件模塊中實現服務
libobs / obs-data.h –用於管理libobs對象的設置
libobs / obs-properties.h –用於爲libobs對象生成屬性
libobs / graphics / graphics.h –用於圖形渲染

目錄結構

結構如下：

其中比較重要的是：

ALL_BUILD

整個項目通過它來啓動，直接啓動obs會有部分文件找不到。

obs

主程序

obs-ffmpeg

obs通過調用ffmpeg api來實現推流錄像等功能，以插件的方式實現

obs-x264

也是插件方式實現x264編碼，這裏後續如果要爲obs增加編碼方式比如h265等可以參考此插件源碼

w32-pthreads

obs發送數據流線程，用的是另外一個開源項目，功能比較強大，詳細信息可以打開源碼註釋查看，這裏特別注意線程裏的互斥鎖，我在調試中很多obs的問題都是使用沒有及時釋放的資源引起的。

libobs

obs視頻採集線程

推流部分關鍵函數源碼簡介

點擊開始錄製，obs將會調用ui部分代碼讀取錄像設置參數：
位於\UI\window-basic-main-outputs.cpp

bool AdvancedOutput::StartRecording()
{
	const char *path;
	const char *recFormat;
	const char *filenameFormat;
	bool noSpace = false;
	bool overwriteIfExists = false;

	if (!useStreamEncoder) {
		if (!ffmpegOutput) {
			UpdateRecordingSettings();
		}
	} else if (!obs_output_active(streamOutput)) {
		UpdateStreamSettings();
	}

	UpdateAudioSettings();

	if (!Active())
		SetupOutputs();

	if (!ffmpegOutput || ffmpegRecording) {
		path = config_get_string(main->Config(), "AdvOut",
					 ffmpegRecording ? "FFFilePath"
							 : "RecFilePath");
		recFormat = config_get_string(main->Config(), "AdvOut",
					      ffmpegRecording ? "FFExtension"
							      : "RecFormat");
		filenameFormat = config_get_string(main->Config(), "Output",
						   "FilenameFormatting");
		overwriteIfExists = config_get_bool(main->Config(), "Output",
						    "OverwriteIfExists");
		noSpace = config_get_bool(main->Config(), "AdvOut",
					  ffmpegRecording
						  ? "FFFileNameWithoutSpace"
						  : "RecFileNameWithoutSpace");

		os_dir_t *dir = path && path[0] ? os_opendir(path) : nullptr;

		if (!dir) {
			if (main->isVisible())
				OBSMessageBox::warning(
					main, QTStr("Output.BadPath.Title"),
					QTStr("Output.BadPath.Text"));
			else
				main->SysTrayNotify(
					QTStr("Output.BadPath.Text"),
					QSystemTrayIcon::Warning);
			return false;
		}

		os_closedir(dir);

		string strPath;
		strPath += path;

		char lastChar = strPath.back();
		if (lastChar != '/' && lastChar != '\\')
			strPath += "/";

		strPath += GenerateSpecifiedFilename(recFormat, noSpace,
						     filenameFormat);
		ensure_directory_exists(strPath);
		if (!overwriteIfExists)
			FindBestFilename(strPath, noSpace);

		obs_data_t *settings = obs_data_create();
		obs_data_set_string(settings, ffmpegRecording ? "url" : "path",
				    strPath.c_str());

		obs_output_update(fileOutput, settings);

		obs_data_release(settings);
	}

	if (!obs_output_start(fileOutput)) {
		QString error_reason;
		const char *error = obs_output_get_last_error(fileOutput);
		if (error)
			error_reason = QT_UTF8(error);
		else
			error_reason = QTStr("Output.StartFailedGeneric");
		QMessageBox::critical(main,
				      QTStr("Output.StartRecordingFailed"),
				      error_reason);
		return false;
	}

	return true;
}

讀取完畢後，將參數應用於obs同時修改視頻編碼和音頻編碼設置，同時更新obs程序運行參數

inline void AdvancedOutput::SetupFFmpeg()
{
	const char *url = config_get_string(main->Config(), "AdvOut", "FFURL");
	int vBitrate = config_get_int(main->Config(), "AdvOut", "FFVBitrate");
	int gopSize = config_get_int(main->Config(), "AdvOut", "FFVGOPSize");
	bool rescale = config_get_bool(main->Config(), "AdvOut", "FFRescale");
	const char *rescaleRes =
		config_get_string(main->Config(), "AdvOut", "FFRescaleRes");
	const char *formatName =
		config_get_string(main->Config(), "AdvOut", "FFFormat");
	const char *mimeType =
		config_get_string(main->Config(), "AdvOut", "FFFormatMimeType");
	const char *muxCustom =
		config_get_string(main->Config(), "AdvOut", "FFMCustom");
	const char *vEncoder =
		config_get_string(main->Config(), "AdvOut", "FFVEncoder");
	int vEncoderId =
		config_get_int(main->Config(), "AdvOut", "FFVEncoderId");
	const char *vEncCustom =
		config_get_string(main->Config(), "AdvOut", "FFVCustom");
	int aBitrate = config_get_int(main->Config(), "AdvOut", "FFABitrate");
	int aMixes = config_get_int(main->Config(), "AdvOut", "FFAudioMixes");
	const char *aEncoder =
		config_get_string(main->Config(), "AdvOut", "FFAEncoder");
	int aEncoderId =
		config_get_int(main->Config(), "AdvOut", "FFAEncoderId");
	const char *aEncCustom =
		config_get_string(main->Config(), "AdvOut", "FFACustom");
	obs_data_t *settings = obs_data_create();

	obs_data_set_string(settings, "url", url);
	obs_data_set_string(settings, "format_name", formatName);
	obs_data_set_string(settings, "format_mime_type", mimeType);
	obs_data_set_string(settings, "muxer_settings", muxCustom);
	obs_data_set_int(settings, "gop_size", gopSize);
	obs_data_set_int(settings, "video_bitrate", vBitrate);
	obs_data_set_string(settings, "video_encoder", vEncoder);
	obs_data_set_int(settings, "video_encoder_id", vEncoderId);
	obs_data_set_string(settings, "video_settings", vEncCustom);
	obs_data_set_int(settings, "audio_bitrate", aBitrate);
	obs_data_set_string(settings, "audio_encoder", aEncoder);
	obs_data_set_int(settings, "audio_encoder_id", aEncoderId);
	obs_data_set_string(settings, "audio_settings", aEncCustom);

	if (rescale && rescaleRes && *rescaleRes) {
		int width;
		int height;
		int val = sscanf(rescaleRes, "%dx%d", &width, &height);

		if (val == 2 && width && height) {
			obs_data_set_int(settings, "scale_width", width);
			obs_data_set_int(settings, "scale_height", height);
		}
	}

	obs_output_set_mixers(fileOutput, aMixes);
	obs_output_set_media(fileOutput, obs_get_video(), obs_get_audio());
	obs_output_update(fileOutput, settings);

	obs_data_release(settings);
}

參數設置成功後開始準備輸出，位於：\libobs\obs-output.c

bool obs_output_start(obs_output_t *output)
{
	bool encoded;
	bool has_service;
	if (!obs_output_valid(output, "obs_output_start"))
		return false;
	if (!output->context.data)
		return false;

	has_service = (output->info.flags & OBS_OUTPUT_SERVICE) != 0;
	if (has_service && !obs_service_initialize(output->service, output))
		return false;

	encoded = (output->info.flags & OBS_OUTPUT_ENCODED) != 0;
	if (encoded && output->delay_sec) {
		return obs_output_delay_start(output);
	} else {
		if (obs_output_actual_start(output)) {
			do_output_signal(output, "starting");
			return true;
		}

		return false;
	}
}

輸出流準備好了之後，創建輸出函數線程，開始調用ffmpeg有關函數準備輸出。位於\obs-ffmpeg\obs-ffmpeg-output.c

static bool ffmpeg_output_start(void *data)
{
	struct ffmpeg_output *output = data;
	int ret;

	if (output->connecting)
		return false;

	os_atomic_set_bool(&output->stopping, false);
	output->audio_start_ts = 0;
	output->video_start_ts = 0;
	output->total_bytes = 0;

	ret = pthread_create(&output->start_thread, NULL, start_thread, output);
	return (output->connecting = (ret == 0));
}

然後創建ffmpeg輸出，設置輸出參數，

**avformat_alloc_output_context2(&data->output, output_format, NULL,
			       NULL);**

上面是調用ffmpeg關鍵代碼設置輸出方式，如rtp，rtmp等。下面是完整函數。

static bool ffmpeg_data_init(struct ffmpeg_data *data,
			     struct ffmpeg_cfg *config)
{
	bool is_rtmp = false;

	memset(data, 0, sizeof(struct ffmpeg_data));
	data->config = *config;
	data->num_audio_streams = config->audio_mix_count;
	data->audio_tracks = config->audio_tracks;
	if (!config->url || !*config->url)
		return false;

#if LIBAVCODEC_VERSION_INT < AV_VERSION_INT(58, 9, 100)
	av_register_all();
#endif
	avformat_network_init();

	is_rtmp = (astrcmpi_n(config->url, "rtmp://", 7) == 0);

	AVOutputFormat *output_format = av_guess_format(
		is_rtmp ? "flv" : data->config.format_name, data->config.url,
		is_rtmp ? NULL : data->config.format_mime_type);

	if (output_format == NULL) {
		ffmpeg_log_error(
			LOG_WARNING, data,
			"Couldn't find matching output format with "
			"parameters: name=%s, url=%s, mime=%s",
			safe_str(is_rtmp ? "flv" : data->config.format_name),
			safe_str(data->config.url),
			safe_str(is_rtmp ? NULL
					 : data->config.format_mime_type));

		goto fail;
	}

	avformat_alloc_output_context2(&data->output, output_format, NULL,
				       NULL);

	if (!data->output) {
		ffmpeg_log_error(LOG_WARNING, data,
				 "Couldn't create avformat context");
		goto fail;
	}

	if (is_rtmp) {
		data->output->oformat->video_codec = AV_CODEC_ID_H264;
		data->output->oformat->audio_codec = AV_CODEC_ID_AAC;
	} else {
		if (data->config.format_name)
			set_encoder_ids(data);
	}

	if (!init_streams(data))
		goto fail;
	if (!open_output_file(data))
		goto fail;

	av_dump_format(data->output, 0, NULL, 1);

	data->initialized = true;
	return true;

fail:
	blog(LOG_WARNING, "ffmpeg_data_init failed");
	return false;
}

寫入文件頭，調用ffmpeg函數代碼爲：

ret = avformat_write_header(data->output, &dict);

以下爲完整函數代碼：

static inline bool open_output_file(struct ffmpeg_data *data)
{
	AVOutputFormat *format = data->output->oformat;
	int ret;

	AVDictionary *dict = NULL;
	if ((ret = av_dict_parse_string(&dict, data->config.muxer_settings, "=",
					" ", 0))) {
		ffmpeg_log_error(LOG_WARNING, data,
				 "Failed to parse muxer settings: %s\n%s",
				 av_err2str(ret), data->config.muxer_settings);

		av_dict_free(&dict);
		return false;
	}

	if (av_dict_count(dict) > 0) {
		struct dstr str = {0};

		AVDictionaryEntry *entry = NULL;
		while ((entry = av_dict_get(dict, "", entry,
					    AV_DICT_IGNORE_SUFFIX)))
			dstr_catf(&str, "\n\t%s=%s", entry->key, entry->value);

		blog(LOG_INFO, "Using muxer settings: %s", str.array);
		dstr_free(&str);
	}

	if ((format->flags & AVFMT_NOFILE) == 0) {
		ret = avio_open2(&data->output->pb, data->config.url,
				 AVIO_FLAG_WRITE, NULL, &dict);
		if (ret < 0) {
			ffmpeg_log_error(LOG_WARNING, data,
					 "Couldn't open '%s', %s",
					 data->config.url, av_err2str(ret));
			av_dict_free(&dict);
			return false;
		}
	}

	strncpy(data->output->filename, data->config.url,
		sizeof(data->output->filename));
	data->output->filename[sizeof(data->output->filename) - 1] = 0;

	ret = avformat_write_header(data->output, &dict);
	if (ret < 0) {
		ffmpeg_log_error(LOG_WARNING, data, "Error opening '%s': %s",
				 data->config.url, av_err2str(ret));
		return false;
	}

	if (av_dict_count(dict) > 0) {
		struct dstr str = {0};

		AVDictionaryEntry *entry = NULL;
		while ((entry = av_dict_get(dict, "", entry,
					    AV_DICT_IGNORE_SUFFIX)))
			dstr_catf(&str, "\n\t%s=%s", entry->key, entry->value);

		blog(LOG_INFO, "Invalid muxer settings: %s", str.array);
		dstr_free(&str);
	}

	av_dict_free(&dict);

	return true;
}

創建數據線程，設置視頻流，音頻流編碼，然後捕獲數據流開始輸出

static bool try_connect(struct ffmpeg_output *output)
{
	video_t *video = obs_output_video(output->output);
	const struct video_output_info *voi = video_output_get_info(video);
	struct ffmpeg_cfg config;
	obs_data_t *settings;
	bool success;
	int ret;

	settings = obs_output_get_settings(output->output);

	obs_data_set_default_int(settings, "gop_size", 120);

	config.url = obs_data_get_string(settings, "url");
	config.format_name = get_string_or_null(settings, "format_name");
	config.format_mime_type =
		get_string_or_null(settings, "format_mime_type");
	config.muxer_settings = obs_data_get_string(settings, "muxer_settings");
	config.video_bitrate = (int)obs_data_get_int(settings, "video_bitrate");
	config.audio_bitrate = (int)obs_data_get_int(settings, "audio_bitrate");
	config.gop_size = (int)obs_data_get_int(settings, "gop_size");
	config.video_encoder = get_string_or_null(settings, "video_encoder");
	config.video_encoder_id =
		(int)obs_data_get_int(settings, "video_encoder_id");
	config.audio_encoder = get_string_or_null(settings, "audio_encoder");
	config.audio_encoder_id =
		(int)obs_data_get_int(settings, "audio_encoder_id");
	config.video_settings = obs_data_get_string(settings, "video_settings");
	config.audio_settings = obs_data_get_string(settings, "audio_settings");
	config.scale_width = (int)obs_data_get_int(settings, "scale_width");
	config.scale_height = (int)obs_data_get_int(settings, "scale_height");
	config.width = (int)obs_output_get_width(output->output);
	config.height = (int)obs_output_get_height(output->output);
	config.format =
		obs_to_ffmpeg_video_format(video_output_get_format(video));
	config.audio_tracks = (int)obs_output_get_mixers(output->output);
	config.audio_mix_count = get_audio_mix_count(config.audio_tracks);

	if (format_is_yuv(voi->format)) {
		config.color_range = voi->range == VIDEO_RANGE_FULL
					     ? AVCOL_RANGE_JPEG
					     : AVCOL_RANGE_MPEG;
		config.color_space = voi->colorspace == VIDEO_CS_709
					     ? AVCOL_SPC_BT709
					     : AVCOL_SPC_BT470BG;
	} else {
		config.color_range = AVCOL_RANGE_UNSPECIFIED;
		config.color_space = AVCOL_SPC_RGB;
	}

	if (config.format == AV_PIX_FMT_NONE) {
		blog(LOG_DEBUG, "invalid pixel format used for FFmpeg output");
		return false;
	}

	if (!config.scale_width)
		config.scale_width = config.width;
	if (!config.scale_height)
		config.scale_height = config.height;

	success = ffmpeg_data_init(&output->ff_data, &config);
	obs_data_release(settings);

	if (!success) {
		if (output->ff_data.last_error) {
			obs_output_set_last_error(output->output,
						  output->ff_data.last_error);
		}
		ffmpeg_data_free(&output->ff_data);
		return false;
	}

	struct audio_convert_info aci = {.format =
						 output->ff_data.audio_format};

	output->active = true;

	if (!obs_output_can_begin_data_capture(output->output, 0))
		return false;

	ret = pthread_create(&output->write_thread, NULL, write_thread, output);
	if (ret != 0) {
		ffmpeg_log_error(LOG_WARNING, &output->ff_data,
				 "ffmpeg_output_start: failed to create write "
				 "thread.");
		ffmpeg_output_full_stop(output);
		return false;
	}

	obs_output_set_video_conversion(output->output, NULL);
	obs_output_set_audio_conversion(output->output, &aci);
	obs_output_begin_data_capture(output->output, 0);
	output->write_thread_active = true;
	return true;
}

線程設置完畢後，開始通過線程寫入數據，輸出

static void *write_thread(void *data)
{
	struct ffmpeg_output *output = data;

	while (os_sem_wait(output->write_sem) == 0) {
		/* check to see if shutting down */
		if (os_event_try(output->stop_event) == 0)
			break;

		int ret = process_packet(output);
		if (ret != 0) {
			int code = OBS_OUTPUT_ERROR;

			pthread_detach(output->write_thread);
			output->write_thread_active = false;

			if (ret == -ENOSPC)
				code = OBS_OUTPUT_NO_SPACE;

			obs_output_signal_stop(output->output, code);
			ffmpeg_deactivate(output);
			break;
		}
	}

	output->active = false;
	return NULL;
}

線程將反覆調用下面函數處理數據包，注意這裏線程有互斥鎖判斷，修改不當容易造成程序崩潰。

static int process_packet(struct ffmpeg_output *output)
{
	AVPacket packet;
	bool new_packet = false;
	int ret;

	pthread_mutex_lock(&output->write_mutex);
	if (output->packets.num) {
		packet = output->packets.array[0];
		da_erase(output->packets, 0);
		new_packet = true;
	}
	pthread_mutex_unlock(&output->write_mutex);

	if (!new_packet)
		return 0;

	/*blog(LOG_DEBUG, "size = %d, flags = %lX, stream = %d, "
			"packets queued: %lu",
			packet.size, packet.flags,
			packet.stream_index, output->packets.num);*/

	if (stopping(output)) {
		uint64_t sys_ts = get_packet_sys_dts(output, &packet);
		if (sys_ts >= output->stop_ts) {
			ffmpeg_output_full_stop(output);
			return 0;
		}
	}

	output->total_bytes += packet.size;

	ret = av_interleaved_write_frame(output->ff_data.output, &packet);
	if (ret < 0) {
		av_free_packet(&packet);
		ffmpeg_log_error(LOG_WARNING, &output->ff_data,
				 "receive_audio: Error writing packet: %s",
				 av_err2str(ret));
		return ret;
	}

	return 0;
}

點擊停止錄製後，線程將會一步步釋放資源。工作涉及整個流程大體如上，後續可能會補充。
附錄國人寫的一個ffmpeg官方函數調用實現rtmp或者rtp數據傳輸開源項目：
https://github.com/leixiaohua1020/simplest_ffmpeg_streamer/blob/master/simplest_ffmpeg_streamer/simplest_ffmpeg_streamer.cpp