avfvideosrc: BUFFER_QUEUE_SIZE too small

Submitted by Ilya Konstantinov

Assigned to Ilya Konstantinov

Link to original bug (#747270)

Description

In avfvideosrc.m, we have:

#define BUFFER_QUEUE_SIZE 2

This buffer queue is used in a producer-consumer fashion between the AV capture callbacks (on AVFoundation's thread) and the element (on the main thread).

With such a small queue, we were constantly:

a) losing performance due to the main thread going to sleep constantly

b) periodically dropping frames in this code:

if ([bufQueue count] == BUFFER_QUEUE_SIZE)
[bufQueue removeLastObject];

Increasing the queue size to e.g. 32 improves performance significantly. On iPhone 5s, improvement of ~7% is seen in the following pipeline:

avfvideosrc device-index=0 ! video/x-raw,width=1280,height=720,framerate=30/1 ! vtenc_h264 bitrate=400 ! fakesink