[FFmpeg-devel] [PATCH v4] avcodec/v4l2_m2m: handle the v4l2 eos event

[Ming Qian]

when the last frame of capture is dequeueed,
driver may send this V4L2_EVENT_EOS event,
If this event is received, then the capture buffers have been flushed and
avcodec_receive_packet()/avcodec_receive_frame() can return AVERROR_EOF.
Otherwise, the draining continues until all the capture buffers have been dequeued or VIDIOC_DQBUF ioctl returns an EPIPE error.

Some devices may not support V4L2_EVENT_EOS.
This is logged as a warning message and not treated as a fatal error during initialization.

Without this patch imx8qm often hangs at the end of encoding/decoding when
flushing the capture buffers

Signed-off-by: Ming Qian <ming.qian at nxp.com>
---
 libavcodec/v4l2_context.c |  6 ++++++
 libavcodec/v4l2_m2m_dec.c |  8 ++++++++
 libavcodec/v4l2_m2m_enc.c | 19 +++++++++++++++++++
 3 files changed, 33 insertions(+)

diff --git a/libavcodec/v4l2_context.c b/libavcodec/v4l2_context.c
index 8110bbb555..6b1f65fe4c 100644
--- a/libavcodec/v4l2_context.c
+++ b/libavcodec/v4l2_context.c
@@ -154,6 +154,7 @@ static inline void v4l2_save_to_context(V4L2Context* ctx, struct v4l2_format_upd
 }
 
 /**
+ * handle resolution change event and end of stream event
  * returns 1 if reinit was successful, negative if it failed
  * returns 0 if reinit was not executed
  */
@@ -171,6 +172,11 @@ static int v4l2_handle_event(V4L2Context *ctx)
         return 0;
     }
 
+    if (evt.type == V4L2_EVENT_EOS) {
+        ctx->done = 1;
+        return 0;
+    }
+
     if (evt.type != V4L2_EVENT_SOURCE_CHANGE)
         return 0;
 
diff --git a/libavcodec/v4l2_m2m_dec.c b/libavcodec/v4l2_m2m_dec.c
index d666edffe4..9989649784 100644
--- a/libavcodec/v4l2_m2m_dec.c
+++ b/libavcodec/v4l2_m2m_dec.c
@@ -123,6 +123,14 @@ static int v4l2_prepare_decoder(V4L2m2mContext *s)
         }
     }
 
+    memset(&sub, 0, sizeof(sub));
+    sub.type = V4L2_EVENT_EOS;
+    ret = ioctl(s->fd, VIDIOC_SUBSCRIBE_EVENT, &sub);
+    if (ret < 0) {
+        av_log(s->avctx, AV_LOG_WARNING,
+                "the v4l2 driver does not support end of stream VIDIOC_SUBSCRIBE_EVENT\n");
+    }
+
     return 0;
 }
 
diff --git a/libavcodec/v4l2_m2m_enc.c b/libavcodec/v4l2_m2m_enc.c
index 84de63ec9d..78cf9ba47a 100644
--- a/libavcodec/v4l2_m2m_enc.c
+++ b/libavcodec/v4l2_m2m_enc.c
@@ -155,6 +155,23 @@ static int v4l2_check_b_frame_support(V4L2m2mContext *s)
     return AVERROR_PATCHWELCOME;
 }
 
+static int v4l2_subscribe_eos_event(V4L2m2mContext *s)
+{
+    struct v4l2_event_subscription sub;
+    int ret;
+
+    memset(&sub, 0, sizeof(sub));
+    sub.type = V4L2_EVENT_EOS;
+    ret = ioctl(s->fd, VIDIOC_SUBSCRIBE_EVENT, &sub);
+    if (ret < 0) {
+        av_log(s->avctx, AV_LOG_WARNING,
+                "the v4l2 driver does not support end of stream VIDIOC_SUBSCRIBE_EVENT\n");
+        return ret;
+    }
+
+    return 0;
+}
+
 static int v4l2_prepare_encoder(V4L2m2mContext *s)
 {
     AVCodecContext *avctx = s->avctx;
@@ -164,6 +181,8 @@ static int v4l2_prepare_encoder(V4L2m2mContext *s)
     /**
      * requirements
      */
+    v4l2_subscribe_eos_event(s);
+
     ret = v4l2_check_b_frame_support(s);
     if (ret)
         return ret;
-- 
2.26.0