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examples: Use VideoFrame API in thumbnail example, use RGBX as format and correctly handle stride

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This commit is contained in:
Sebastian Dröge 2021-11-08 20:56:58 +02:00
parent e3a65a3a88
commit 1480c65c32
1 changed files with 38 additions and 25 deletions
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63
examples/src/bin/thumbnail.rs
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@ -3,8 +3,9 @@
// {uridecodebin} - {videoconvert} - {appsink}
// The appsink enforces RGBA so that the image crate can use it. The image crate also requires
// tightly packed pixels, which is the case for RGBA by default in GStreamer.
// The appsink enforces RGBx so that the image crate can use it. The sample layout is passed
// with the correct stride from GStreamer to the image crate as GStreamer does not necessarily
// produce tightly packed pixels, and in case of RGBx never.
use gst::element_error;
use gst::prelude::*;
@ -54,7 +55,7 @@ fn create_pipeline(uri: String, out_path: std::path::PathBuf) -> Result<gst::Pip
// both elements will happen during pre-rolling of the pipeline.
appsink.set_caps(Some(
&gst::Caps::builder("video/x-raw")
.field("format", gst_video::VideoFormat::Rgba.to_str())
.field("format", gst_video::VideoFormat::Rgbx.to_str())
.build(),
));
@ -78,15 +79,15 @@ fn create_pipeline(uri: String, out_path: std::path::PathBuf) -> Result<gst::Pip
gst::FlowError::Error
})?;
let caps = sample.caps().expect("Sample without caps");
let info = gst_video::VideoInfo::from_caps(caps).expect("Failed to parse caps");
// Make sure that we only get a single buffer
if got_snapshot {
return Err(gst::FlowError::Eos);
}
got_snapshot = true;
let caps = sample.caps().expect("Sample without caps");
let info = gst_video::VideoInfo::from_caps(caps).expect("Failed to parse caps");
// At this point, buffer is only a reference to an existing memory region somewhere.
// When we want to access its content, we have to map it while requesting the required
// mode of access (read, read/write).
@ -94,37 +95,49 @@ fn create_pipeline(uri: String, out_path: std::path::PathBuf) -> Result<gst::Pip
// on the machine's main memory itself, but rather in the GPU's memory.
// So mapping the buffer makes the underlying memory region accessible to us.
// See: https://gstreamer.freedesktop.org/documentation/plugin-development/advanced/allocation.html
let map = buffer.map_readable().map_err(|_| {
element_error!(
appsink,
gst::ResourceError::Failed,
("Failed to map buffer readable")
);
let frame = gst_video::VideoFrameRef::from_buffer_ref_readable(buffer, &info)
.map_err(|_| {
element_error!(
appsink,
gst::ResourceError::Failed,
("Failed to map buffer readable")
);
gst::FlowError::Error
})?;
gst::FlowError::Error
})?;
// We only want to have a single buffer and then have the pipeline terminate
println!("Have video frame");
// Calculate a target width/height that keeps the display aspect ratio while having
// a height of 240 pixels
let display_aspect_ratio = (info.width() as f64 * info.par().numer() as f64)
/ (info.height() as f64 * info.par().denom() as f64);
let display_aspect_ratio = (frame.width() as f64 * info.par().numer() as f64)
/ (frame.height() as f64 * info.par().denom() as f64);
let target_height = 240;
let target_width = target_height as f64 * display_aspect_ratio;
// Create an ImageBuffer around the borrowed video frame data from GStreamer.
let img = image::ImageBuffer::<image::Rgba<u8>, _>::from_raw(
info.width(),
info.height(),
map,
)
.expect("Failed to create ImageBuffer, probably a stride mismatch");
// Create a FlatSamples around the borrowed video frame data from GStreamer with
// the correct stride as provided by GStreamer.
let img = image::FlatSamples::<&[u8]> {
samples: frame.plane_data(0).unwrap(),
layout: image::flat::SampleLayout {
channels: 3, // RGB
channel_stride: 1, // 1 byte from component to component
width: frame.width(),
width_stride: 4, // 4 byte from pixel to pixel
height: frame.height(),
height_stride: frame.plane_stride()[0] as usize, // stride from line to line
},
color_hint: Some(image::ColorType::Rgb8),
};
// Scale image to our target dimensions
let scaled_img =
image::imageops::thumbnail(&img, target_width as u32, target_height as u32);
let scaled_img = image::imageops::thumbnail(
&img.as_view::<image::Rgb<u8>>()
.expect("couldn't create image view"),
target_width as u32,
target_height as u32,
);
// Save it at the specific location. This automatically detects the file type
// based on the filename.