Function negotiate_format

rustcv-backend-msmf/src/device.rs:282–328

Negotiates and selects the best video format from available options This function: 1. Gets the presentation descriptor from the MediaSource 2. Extracts the primary video stream descriptor 3. Iterates through all available media types 4. Parses each media type and calculates a match score 5. Selects the format with the highest score # Arguments `source` - The IMFMediaSource to query `config` - Ca

(source: &IMFMediaSource, config: &CameraConfig)

/// # Returns
/// A `NegotiatedFormat` struct with selected resolution, format, and frame rate
fn negotiate_format(source: &IMFMediaSource, config: &CameraConfig) -> Result<NegotiatedFormat> {
    unsafe {
        // Create presentation descriptor to access stream information
        let pd = source
            .CreatePresentationDescriptor()
            .map_err(hresult_to_camera_error)?;
        let mut selected = false.into();
        let mut sd = None;

        // Get the primary video stream descriptor (index 0)
        pd.GetStreamDescriptorByIndex(0, &mut selected, &mut sd)
            .map_err(hresult_to_camera_error)?;
        let sd =
            sd.ok_or_else(|| CameraError::Io(std::io::Error::other("No video stream found")))?;

        // Get media type handler for format enumeration
        let handler = sd.GetMediaTypeHandler().map_err(hresult_to_camera_error)?;
        let count = handler
            .GetMediaTypeCount()
            .map_err(hresult_to_camera_error)?;

        // Early exit if no media types available
        if count == 0 {
            return Err(CameraError::FormatNotSupported);
        }

        // Iterate through media types, tracking best format to avoid unnecessary clones
        let mut best_format: Option<(i32, NegotiatedFormat)> = None;

        for index in 0..count {
            if let Ok(mt) = handler.GetMediaTypeByIndex(index) {
                if let Some((score, fmt)) = parse_media_type(&mt, config) {
                    if best_format
                        .as_ref()
                        .is_none_or(|(best_score, _)| score > *best_score)
                    {
                        best_format = Some((score, fmt));
                    }
                }
            }
        }

        best_format
            .map(|(_, fmt)| fmt)
            .ok_or(CameraError::FormatNotSupported)
    }
}

/// Parses a Media Foundation media type and calculates format score
///