obs录屏核心流程分析
从output入手，梳理一下obs output的结构。这里需要仔细过一遍，因为接下来需要把视频写入Unreal的Rendertarget对象，来渲染成材质。
音频也需要单独接入到Unreal引擎中。梳理的过程中，非核心的逻辑和标记我会去掉，只保留主干。
//碧麟备注版
struct obs_output {
// obs上下文
struct obs_context_data context;
// 输出结构信息
struct obs_output_info info;
/* indicates ownership of the info.id buffer */
bool owns_info_id;
int64_t video_offset;
int64_t audio_offsets[MAX_OUTPUT_AUDIO_ENCODERS];
int64_t highest_audio_ts;
int64_t highest_video_ts;
pthread_t end_data_capture_thread;
int total_frames;
//视频信息指针
video_t *video;
//音频信息指针
audio_t *audio;
//视频编码器
obs_encoder_t *video_encoder;
//音频编码器，因为支持多路音频合成，所以这里用的是数组
obs_encoder_t *audio_encoders[MAX_OUTPUT_AUDIO_ENCODERS];
struct circlebuf audio_buffer[MAX_AUDIO_MIXES][MAX_AV_PLANES];
uint64_t audio_start_ts;
uint64_t video_start_ts;
size_t audio_size;
size_t planes;
size_t sample_rate;
size_t total_audio_frames;
uint32_t scaled_width;
uint32_t scaled_height;
struct video_scale_info video_conversion;
struct audio_convert_info audio_conversion; struct circlebuf caption_data;
float audio_data[MAX_AUDIO_CHANNELS][AUDIO_OUTPUT_FRAMES];
};
看完上面的output结构，我们实际调试一下，点击“屏幕录制”，会进入obs_output_start这个函数，这个函数是个马甲，简单带过
//碧麟精简标注版
bool obs_output_start(obs_output_t *output)
{
bool encoded;
bool has_service;
encoded = (output->info.flags & OBS_OUTPUT_ENCODED) != 0;
if (encoded && output->delay_sec) {
//延迟运行
return obs_output_delay_start(output);
} else {
//实际运行
if (obs_output_actual_start(output)) {
//发送starting signal
do_output_signal(output, "starting");
return true;
}
return false;
}
}接下来是重点
//碧麟精简批注版
bool obs_output_actual_start(obs_output_t *output)
{
bool success = false;
// 第一步，调用outp->info.start,参数是output->context.data
if (output->context.data)
success = output->info.start(output->context.data);
if (success && output->video) {
output->starting_frame_count =
video_output_get_total_frames(output->video);
output->starting_drawn_count = obs->video.total_frames;
output->starting_lagged_count = obs->video.lagged_frames;
}
if (os_atomic_load_long(&output->delay_restart_refs))
os_atomic_dec_long(&output->delay_restart_refs);
output->caption_timestamp = 0;
circlebuf_free(&output->caption_data);
circlebuf_init(&output->caption_data);
return success;
}第一步是，调用outp->info.start,参数是output->context.data
output->info.start应该是一个函数指针，定义如下
// 碧麟精简批注版
// output_info结构 ，主要存储函数指针
struct obs_output_info {
/* required */
const char *id;
uint32_t flags;
const char *(*get_name)(void *type_data);
//创建
void *(*create)(obs_data_t *settings, obs_output_t *output);
//销毁
void (*destroy)(void *data);
//开始
bool (*start)(void *data);
//停止
void (*stop)(void *data, uint64_t ts);
void (*raw_video)(void *data, struct video_data *frame);
void (*raw_audio)(void *data, struct audio_data *frames);
void (*encoded_packet)(void *data, struct encoder_packet *packet);
//get默认设置
void (*get_defaults)(obs_data_t *settings);
//get属性
obs_properties_t *(*get_properties)(void *data);
uint64_t (*get_total_bytes)(void *data);
int (*get_dropped_frames)(void *data);
void *type_data;
/* only used with encoded outputs, separated with semicolon */
const char *encoded_video_codecs;
const char *encoded_audio_codecs;
/* raw audio callback for multi track outputs */
void (*raw_audio2)(void *data, size_t idx, struct audio_data *frames);
};context定义如下
//context数据结构
struct obs_context_data {
char *name;
const char *uuid;
// 这个是最重要的
void *data;
obs_data_t *settings;
signal_handler_t *signals;
proc_handler_t *procs;
enum obs_obj_type type;
struct obs_weak_object *control;
DARRAY(obs_hotkey_id) hotkeys;
DARRAY(obs_hotkey_pair_id) hotkey_pairs;
obs_data_t *hotkey_data;
//多路传输使用，链表
struct obs_context_data *next;
struct obs_context_data **prev_next;
bool private;
};这里，data是context最重要的内容
因为我是用的ffmpeg多路传输做录屏，所以data是一个ffmpeg_muxer
因此output->info.start(output->context.data)在这里展开是这样的结构
static bool ffmpeg_mux_start(void *data)
{
struct ffmpeg_muxer *stream = data;
//读取设置
obs_data_t *settings = obs_output_get_settings(stream->output);
//实际开始执行多路传输
bool success = ffmpeg_mux_start_internal(stream, settings);
obs_data_release(settings);
return success;
}
//碧麟精简批注版
static inline bool ffmpeg_mux_start_internal(struct ffmpeg_muxer *stream,
obs_data_t *settings)
{
//读取保存路径
//调试结果：C:/Users/86180/Videos/2023-03-16 13-36-11.mp4
const char *path = obs_data_get_string(settings, "path");
//设定保存路径
update_encoder_settings(stream, path);
//网路版
if (stream->is_network) {
obs_service_t *service;
service = obs_output_get_service(stream->output);
if (!service)
return false;
path = obs_service_get_url(service);
stream->split_file = false;
} else {
//本地版
stream->max_time =
obs_data_get_int(settings, "max_time_sec") * 1000000LL;
stream->max_size = obs_data_get_int(settings, "max_size_mb") *
(1024 * 1024);
stream->split_file = obs_data_get_bool(settings, "split_file");
stream->allow_overwrite =
obs_data_get_bool(settings, "allow_overwrite");
stream->cur_size = 0;
stream->sent_headers = false;
}
ts_offset_clear(stream);
//录屏信息尝试写本地文件，确保文件可写入
if (!stream->is_network) {
/* ensure output path is writable to avoid generic error
* message.
*
* TODO: remove once ffmpeg-mux is refactored to pass
* errors back */
FILE *test_file = os_fopen(path, "wb");
if (!test_file) {
set_file_not_readable_error(stream, settings, path);
return false;
}
fclose(test_file);
os_unlink(path);
}
//这里会生成一个command
//"D:/dev/obs/obs-studio/build/rundir/Debug/bin/64bit/obs-ffmpeg-mux.exe" "C:/Users/86180/Videos/2023-03-16 14-58-19.mp4" 1 1 h264 850 1280 720 1 1 1 1 1 0 30 1 0 aac "simple_aac" 192 48000 1024 2 "" ""
//可以看出是使用外部程序进行录屏
start_pipe(stream, path);
if (!stream->pipe) {
obs_output_set_last_error(
stream->output, obs_module_text("HelperProcessFailed"));
warn("Failed to create process pipe");
return false;
}
/* write headers and start capture */
os_atomic_set_bool(&stream->active, true);
os_atomic_set_bool(&stream->capturing, true);
stream->total_bytes = 0;
obs_output_begin_data_capture(stream->output, 0);
info("Writing file '%s'...", stream->path.array);
return true;
}ffmpeg_mux实际工作核心逻辑都在这里
可以看出录屏是用这个外部程序obs-ffmpeg-mux.exe来进行的。
认真写好每一行代码
