The V4L2M2M API operates asynchronously, so multiple packets can
be enqueued before getting a batch of frames back. Since it was
only possible to receive a frame by submitting another packet,
there wasn't a way to drain those excess output frames from when
avcodec_receive_frame() returned AVERROR(EAGAIN).
In my testing, this change reduced decode latency of a real-time
60 FPS H.264 stream by approximately 10x (200ms -> 20ms) on a
Raspberry Pi 4.
Signed-off-by: Cameron Gutman <aicomman...@gmail.com>
---
libavcodec/v4l2_m2m_dec.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/libavcodec/v4l2_m2m_dec.c b/libavcodec/v4l2_m2m_dec.c
index 224eb3d5e7..b0c3d30ac8 100644
--- a/libavcodec/v4l2_m2m_dec.c
+++ b/libavcodec/v4l2_m2m_dec.c
@@ -142,8 +142,12 @@ static int v4l2_receive_frame(AVCodecContext *avctx,
AVFrame *frame)
if (!s->buf_pkt.size) {
ret = ff_decode_get_packet(avctx, &s->buf_pkt);
- if (ret < 0 && ret != AVERROR_EOF)
- return ret;
+ if (ret < 0) {
+ if (ret == AVERROR(EAGAIN))
+ return ff_v4l2_context_dequeue_frame(capture, frame, 0);
+ else if (ret != AVERROR_EOF)
+ return ret;
+ }
}
if (s->draining)
--
2.25.1
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