scrcpy/app/src/video_buffer.c

#include "video_buffer.h"

#include <assert.h>
#include <libavutil/avutil.h>
#include <libavformat/avformat.h>

#include "util/log.h"

bool
video_buffer_init(struct video_buffer *vb, bool render_expired_frames) {
    vb->decoding_frame = av_frame_alloc();
    if (!vb->decoding_frame) {
        goto error_0;
    }

    vb->pending_frame = av_frame_alloc();
    if (!vb->pending_frame) {
        goto error_1;
    }

    vb->rendering_frame = av_frame_alloc();
    if (!vb->rendering_frame) {
        goto error_2;
    }

    bool ok = sc_mutex_init(&vb->mutex);
    if (!ok) {
        goto error_3;
    }

    vb->render_expired_frames = render_expired_frames;
    if (render_expired_frames) {
        ok = sc_cond_init(&vb->pending_frame_consumed_cond);
        if (!ok) {
            sc_mutex_destroy(&vb->mutex);
            goto error_2;
        }
        // interrupted is not used if expired frames are not rendered
        // since offering a frame will never block
        vb->interrupted = false;
    }

    // there is initially no rendering frame, so consider it has already been
    // consumed
    vb->pending_frame_consumed = true;

    return true;

error_3:
    av_frame_free(&vb->rendering_frame);
error_2:
    av_frame_free(&vb->pending_frame);
error_1:
    av_frame_free(&vb->decoding_frame);
error_0:
    return false;
}

void
video_buffer_destroy(struct video_buffer *vb) {
    if (vb->render_expired_frames) {
        sc_cond_destroy(&vb->pending_frame_consumed_cond);
    }
    sc_mutex_destroy(&vb->mutex);
    av_frame_free(&vb->rendering_frame);
    av_frame_free(&vb->pending_frame);
    av_frame_free(&vb->decoding_frame);
}

static void
video_buffer_swap_decoding_frame(struct video_buffer *vb) {
    sc_mutex_assert(&vb->mutex);
    AVFrame *tmp = vb->decoding_frame;
    vb->decoding_frame = vb->pending_frame;
    vb->pending_frame = tmp;
}

static void
video_buffer_swap_rendering_frame(struct video_buffer *vb) {
    sc_mutex_assert(&vb->mutex);
    AVFrame *tmp = vb->rendering_frame;
    vb->rendering_frame = vb->pending_frame;
    vb->pending_frame = tmp;
}

void
video_buffer_offer_decoded_frame(struct video_buffer *vb,
                                 bool *previous_frame_skipped) {
    sc_mutex_lock(&vb->mutex);
    if (vb->render_expired_frames) {
        // wait for the current (expired) frame to be consumed
        while (!vb->pending_frame_consumed && !vb->interrupted) {
            sc_cond_wait(&vb->pending_frame_consumed_cond, &vb->mutex);
        }
    }

    video_buffer_swap_decoding_frame(vb);

    *previous_frame_skipped = !vb->pending_frame_consumed;
    vb->pending_frame_consumed = false;

    sc_mutex_unlock(&vb->mutex);
}

const AVFrame *
video_buffer_take_rendering_frame(struct video_buffer *vb) {
    sc_mutex_lock(&vb->mutex);
    assert(!vb->pending_frame_consumed);
    vb->pending_frame_consumed = true;

    video_buffer_swap_rendering_frame(vb);

    if (vb->render_expired_frames) {
        // unblock video_buffer_offer_decoded_frame()
        sc_cond_signal(&vb->pending_frame_consumed_cond);
    }
    sc_mutex_unlock(&vb->mutex);

    // rendering_frame is only written from this thread, no need to lock
    return vb->rendering_frame;
}

void
video_buffer_interrupt(struct video_buffer *vb) {
    if (vb->render_expired_frames) {
        sc_mutex_lock(&vb->mutex);
        vb->interrupted = true;
        sc_mutex_unlock(&vb->mutex);
        // wake up blocking wait
        sc_cond_signal(&vb->pending_frame_consumed_cond);
    }
}