[FFmpeg-cvslog] avcodec/v4l2_context: send start decode command after dynamic resolution change event

[Ming Qian]

ffmpeg | branch: release/5.0 | Ming Qian <ming.qian at nxp.com> | Tue Jan  4 17:08:32 2022 +0800| [832aae6c8684041a874943d4dc2f9272869809c9] | committer: Andriy Gelman

avcodec/v4l2_context: send start decode command after dynamic resolution change event

Fixes decoding of sample https://streams.videolan.org/ffmpeg/incoming/720p60.mp4
on RPi4 after kernel driver commit:
staging: bcm2835-codec: Format changed should trigger drain

Reference:
linux/Documentation/userspace-api/media/v4l/dev-decoder.rst
    "A source change triggers an implicit decoder drain, similar to the
     explicit Drain sequence. The decoder is stopped after it completes.
     The decoding process must be resumed with either a pair of calls to
     VIDIOC_STREAMOFF and VIDIOC_STREAMON on the CAPTURE queue, or a call to
     VIDIOC_DECODER_CMD with the V4L2_DEC_CMD_START command."

Reviewed-by: Andriy Gelman <andriy.gelman at gmail.com>
Signed-off-by: Ming Qian <ming.qian at nxp.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=832aae6c8684041a874943d4dc2f9272869809c9
---

 libavcodec/v4l2_context.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/libavcodec/v4l2_context.c b/libavcodec/v4l2_context.c
index dda5157698..a181f884d2 100644
--- a/libavcodec/v4l2_context.c
+++ b/libavcodec/v4l2_context.c
@@ -153,6 +153,21 @@ static inline void v4l2_save_to_context(V4L2Context* ctx, struct v4l2_format_upd
     }
 }
 
+static int v4l2_start_decode(V4L2Context *ctx)
+{
+    struct v4l2_decoder_cmd cmd = {
+        .cmd = V4L2_DEC_CMD_START,
+        .flags = 0,
+    };
+    int ret;
+
+    ret = ioctl(ctx_to_m2mctx(ctx)->fd, VIDIOC_DECODER_CMD, &cmd);
+    if (ret)
+        return AVERROR(errno);
+
+    return 0;
+}
+
 /**
  * handle resolution change event and end of stream event
  * returns 1 if reinit was successful, negative if it failed
@@ -190,6 +205,9 @@ static int v4l2_handle_event(V4L2Context *ctx)
         s->capture.height = v4l2_get_height(&cap_fmt);
         s->capture.width = v4l2_get_width(&cap_fmt);
         s->capture.sample_aspect_ratio = v4l2_get_sar(&s->capture);
+    } else {
+        v4l2_start_decode(ctx);
+        return 0;
     }
 
     if (reinit)