[libcamera-devel] [PATCH v3 5/8] libcamera: properties: Add FrameDurationLimits

[Jacopo Mondi]

Add a camera property to express the minimum and maximum frame durations.

Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
---

Cc Naush and Dave as this could potentially conflict with their on-going FPS
handling series. Sending it out for discussion.

---
 src/libcamera/property_ids.yaml | 47 +++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)

diff --git a/src/libcamera/property_ids.yaml b/src/libcamera/property_ids.yaml
index ce627fa042ba..d703ab31eaac 100644
--- a/src/libcamera/property_ids.yaml
+++ b/src/libcamera/property_ids.yaml
@@ -386,4 +386,51 @@ controls:
                               |                    |
                               |                    |
                               +--------------------+
+
+  - FrameDurationLimits:
+      type: int32_t
+      size: [2]
+      description: |
+        The camera supported frame durations interval.
+
+        This property reports the camera minimum and maximum frame durations (in
+        this order) expressed in nanoseconds to report the limits of the
+        achievable frame rate.
+
+        Camera devices should here report durations calculated by inspecting the
+        camera sensor supported frame rate interval, and adding to it any
+        known additional delay caused by the image acquisition process that
+        incurs in the time between a frame is captured and delivered to
+        applications.
+
+        The here reported durations represent the time interval that occurs
+        between the delivery of two consecutive frames for the fastest and
+        slower streams, without considering additional delays introduced by the
+        sharing of system resources when multiple streams are captured at the
+        same time.
+
+        This implies that the minimum reported frame duration, which corresponds
+        to the highest possible camera frame rate, is calculated without taking
+        into consideration how multiple streams capture requests sent to
+        the camera as part of the same capture session might influence the frame
+        delivery rate by, in example, introducing delays due to the requirement
+        of time-sharing components part of the image acquisition pipeline. In
+        example, request containing two scaled-down streams might require
+        time-sharing the single scaler available in the system, introducing an
+        additional delay that prevents the camera to deliver frames at the
+        here reported rate.
+
+        In the same way, the maximum frame duration, which corresponds to the
+        lowest possible frame rate, does not take into consideration additional
+        processing delays introduced by image encoding and processing that
+        happens sporadically, in example, to produce still images in JPEG
+        format.
+
+        As a consequence, application should inspect this property to know the
+        camera capability limits, but should not assume the here reported values
+        are achievable under all circumstances.
+
+        # \todo Expand to better describe how stalling streams (ie JPEG) impacts
+        # the frame rate calculation.
+
 ...
--
2.27.0