Le samedi 17 novembre 2018 à 12:37 +0100, Hans Verkuil a écrit : > > > Does V4L2_CID_MIN_BUFFERS_FOR_CAPTURE make any sense for encoders? > > > > We do account for it in GStreamer (the capture/output handling is > > generic), but I don't know if it's being used anywhere. > > Do you use this value directly for REQBUFS, or do you use it as the minimum > value but in practice use more buffers? We add more buffers to that value. We assume this value is what will be held by the driver, hence without adding some buffers, the driver would go idle as soon as one is dequeued. We also need to allocate for the importing driver. In general, if we have a pipeline with Driver A sending to Driver B, both driver will require a certain amount of buffers to operate. E.g. with DRM display, the driver will hold on 1 buffer (the scannout buffer). In GStreamer, it's implemented generically, so we do: MIN_BUFFERS_FOR + remote_min + 1 If only MIN_BUFFERS_FOR was allocated, ignoring remote driver requirement, the streaming will likely get stuck. regards, Nicolas
