Straw Lab H264 metadata, version 1

Metadata is serialized as JSON using serde. The Rust definition used is:

#[derive(Debug, PartialEq, Clone, Serialize, Deserialize)]
pub struct H264Metadata {
    /// Version of this structure
    ///
    /// For v1, should be equal to `https://strawlab.org/h264-metadata/v1/`.
    ///
    /// This field must always be serialized first.
    pub version: String,
    pub writing_app: String,
    pub creation_time: chrono::DateTime<chrono::FixedOffset>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub camera_name: Option<String>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub gamma: Option<f32>,
}