forked from mirrors/gstreamer-rs
examples: Add an example that registers a custom GstMeta and makes use of it
The meta contains a Rust String as a label for the buffer. It is added on buffers passed into an appsrc and retrieved from the buffers provided by an appsink.
This commit is contained in:
Sebastian Dröge
parent
9f422c25d9
commit
9b4117ea71
2 changed files with 299 additions and 0 deletions
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@ -66,6 +66,9 @@ name = "appsrc"
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name = "custom_events"
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required-features = ["v1_10"]
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[[bin]]
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name = "custom_meta"
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[[bin]]
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name = "decodebin"
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296
examples/src/bin/custom_meta.rs
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296
examples/src/bin/custom_meta.rs
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@ -0,0 +1,296 @@
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// This example demonstrates how custom GstMeta can be defined and used on buffers.
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//
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// It simply attaches a GstMeta with a Rust String to buffers that are passed into
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// an appsrc and retrieves them again from an appsink.
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#[macro_use]
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extern crate gstreamer as gst;
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use gst::prelude::*;
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extern crate gstreamer_app as gst_app;
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#[path = "../examples-common.rs"]
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mod examples_common;
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mod custom_meta {
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use gst::gst_sys;
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use gst::prelude::*;
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use std::fmt;
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use std::ptr;
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// Public Rust type for the custom meta.
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#[repr(C)]
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pub struct CustomMeta(imp::CustomMeta);
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// Metas must be Send+Sync.
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unsafe impl Send for CustomMeta {}
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unsafe impl Sync for CustomMeta {}
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impl CustomMeta {
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// Add a new custom meta to the buffer with the given label.
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pub fn add(
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buffer: &mut gst::BufferRef,
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label: String,
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) -> gst::MetaRefMut<Self, gst::meta::Standalone> {
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unsafe {
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// First add it: this will store an empty label via custom_meta_init().
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let meta = gst_sys::gst_buffer_add_meta(
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buffer.as_mut_ptr(),
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imp::custom_meta_get_info(),
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ptr::null_mut(),
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) as *mut imp::CustomMeta;
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// Then actually set the label.
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{
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let meta = &mut *meta;
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meta.label = label;
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}
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Self::from_mut_ptr(buffer, meta)
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}
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}
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// Retrieve the stored label.
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pub fn get_label(&self) -> &str {
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self.0.label.as_str()
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}
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}
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// Trait to allow using the gst::Buffer API with this meta.
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unsafe impl MetaAPI for CustomMeta {
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type GstType = imp::CustomMeta;
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fn get_meta_api() -> glib::Type {
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imp::custom_meta_api_get_type()
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}
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}
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impl fmt::Debug for CustomMeta {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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f.debug_struct("CustomMeta")
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.field("label", &self.get_label())
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.finish()
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}
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}
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// Actual unsafe implementation of the meta.
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mod imp {
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use glib::glib_sys;
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use glib::translate::*;
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use gst::gst_sys;
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use gst::prelude::*;
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use once_cell::sync::Lazy;
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use std::mem;
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use std::ptr;
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// This is the C type that is actually stored as meta inside the buffers.
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#[repr(C)]
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pub struct CustomMeta {
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parent: gst_sys::GstMeta,
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pub(super) label: String,
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}
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// Function to register the meta API and get a type back.
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pub(super) fn custom_meta_api_get_type() -> glib::Type {
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static TYPE: Lazy<glib::Type> = Lazy::new(|| unsafe {
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let t = from_glib(gst_sys::gst_meta_api_type_register(
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b"MyCustomMetaAPI\0".as_ptr() as *const _,
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// We provide no tags here as our meta is just a label and does
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// not refer to any specific aspect of the buffer
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[ptr::null::<std::os::raw::c_char>()].as_ptr() as *mut *const _,
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));
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assert_ne!(t, glib::Type::Invalid);
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t
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});
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*TYPE
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}
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// Initialization function for our meta. This needs to ensure all fields are correctly
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// initialized. They will contain random memory before.
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unsafe extern "C" fn custom_meta_init(
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meta: *mut gst_sys::GstMeta,
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_params: glib_sys::gpointer,
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_buffer: *mut gst_sys::GstBuffer,
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) -> glib_sys::gboolean {
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let meta = &mut *(meta as *mut CustomMeta);
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// Need to initialize all our fields correctly here
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ptr::write(&mut meta.label, String::new());
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true.to_glib()
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}
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// Free function for our meta. This needs to free/drop all memory we allocated.
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unsafe extern "C" fn custom_meta_free(
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meta: *mut gst_sys::GstMeta,
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_buffer: *mut gst_sys::GstBuffer,
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) {
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let meta = &mut *(meta as *mut CustomMeta);
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// Need to free/drop all our fields here.
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ptr::drop_in_place(&mut meta.label);
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}
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// Transform function for our meta. This needs to get it from the old buffer to the new one
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// in a way that is compatible with the transformation type. In this case we just always
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// copy it over.
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unsafe extern "C" fn custom_meta_transform(
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dest: *mut gst_sys::GstBuffer,
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meta: *mut gst_sys::GstMeta,
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_buffer: *mut gst_sys::GstBuffer,
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_type_: glib_sys::GQuark,
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_data: glib_sys::gpointer,
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) -> glib_sys::gboolean {
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let meta = &mut *(meta as *mut CustomMeta);
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// We simply copy over our meta here. Other metas might have to look at the type
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// and do things conditional on that, or even just drop the meta.
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super::CustomMeta::add(gst::BufferRef::from_mut_ptr(dest), meta.label.clone());
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true.to_glib()
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}
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// Register the meta itself with its functions.
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pub(super) fn custom_meta_get_info() -> *const gst_sys::GstMetaInfo {
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struct MetaInfo(ptr::NonNull<gst_sys::GstMetaInfo>);
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unsafe impl Send for MetaInfo {}
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unsafe impl Sync for MetaInfo {}
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static META_INFO: Lazy<MetaInfo> = Lazy::new(|| unsafe {
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MetaInfo(
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ptr::NonNull::new(gst_sys::gst_meta_register(
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custom_meta_api_get_type().to_glib(),
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b"MyCustomMeta\0".as_ptr() as *const _,
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mem::size_of::<CustomMeta>(),
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Some(custom_meta_init),
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Some(custom_meta_free),
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Some(custom_meta_transform),
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) as *mut gst_sys::GstMetaInfo)
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.expect("Failed to register meta API"),
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)
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});
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META_INFO.0.as_ptr()
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}
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}
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}
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fn example_main() {
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gst::init().unwrap();
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// This creates a pipeline with appsrc and appsink.
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let pipeline = gst::Pipeline::new(None);
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let appsrc = gst::ElementFactory::make("appsrc", None)
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.unwrap()
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.downcast::<gst_app::AppSrc>()
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.unwrap();
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let appsink = gst::ElementFactory::make("appsink", None)
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.unwrap()
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.downcast::<gst_app::AppSink>()
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.unwrap();
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pipeline.add(&appsrc).unwrap();
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pipeline.add(&appsink).unwrap();
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appsrc.link(&appsink).unwrap();
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// Our buffer counter, that is stored in the mutable environment
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// of the closure of the need-data callback.
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let mut i = 0;
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appsrc.set_callbacks(
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gst_app::AppSrcCallbacks::new()
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.need_data(move |appsrc, _| {
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// We only produce 5 buffers.
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if i == 5 {
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let _ = appsrc.end_of_stream();
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return;
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}
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println!("Producing buffer {}", i);
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// Add a custom meta with a label to this buffer.
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let mut buffer = gst::Buffer::new();
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{
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let buffer = buffer.get_mut().unwrap();
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custom_meta::CustomMeta::add(buffer, format!("This is buffer {}", i));
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}
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i += 1;
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// appsrc already handles the error here for us.
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let _ = appsrc.push_buffer(buffer);
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})
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.build(),
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);
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// Getting data out of the appsink is done by setting callbacks on it.
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// The appsink will then call those handlers, as soon as data is available.
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appsink.set_callbacks(
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gst_app::AppSinkCallbacks::new()
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// Add a handler to the "new-sample" signal.
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.new_sample(|appsink| {
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// Pull the sample in question out of the appsink's buffer.
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let sample = appsink.pull_sample().map_err(|_| gst::FlowError::Eos)?;
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let buffer = sample.get_buffer().ok_or_else(|| {
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gst_element_error!(
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appsink,
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gst::ResourceError::Failed,
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("Failed to get buffer from appsink")
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);
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gst::FlowError::Error
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})?;
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// Retrieve the custom meta from the buffer and print it.
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let meta = buffer
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.get_meta::<custom_meta::CustomMeta>()
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.expect("No custom meta found");
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println!("Got buffer with label: {}", meta.get_label());
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Ok(gst::FlowSuccess::Ok)
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})
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.build(),
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);
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// Actually start the pipeline.
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pipeline
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.set_state(gst::State::Playing)
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.expect("Unable to set the pipeline to the `Playing` state");
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let pipeline = pipeline.dynamic_cast::<gst::Pipeline>().unwrap();
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let bus = pipeline
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.get_bus()
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.expect("Pipeline without bus. Shouldn't happen!");
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// And run until EOS or an error happened.
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for msg in bus.iter_timed(gst::CLOCK_TIME_NONE) {
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use gst::MessageView;
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match msg.view() {
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MessageView::Eos(..) => break,
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MessageView::Error(err) => {
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println!(
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"Error from {:?}: {} ({:?})",
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err.get_src().map(|s| s.get_path_string()),
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err.get_error(),
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err.get_debug()
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);
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break;
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}
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_ => (),
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}
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}
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// Finally shut down everything.
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pipeline
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.set_state(gst::State::Null)
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.expect("Unable to set the pipeline to the `Null` state");
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}
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fn main() {
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// tutorials_common::run is only required to set up the application environent on macOS
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// (but not necessary in normal Cocoa applications where this is set up automatically).
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examples_common::run(example_main);
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}
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