[FFmpeg-devel] [PATCH v4 2/3] avcodec/v4l2_context: resume the decoding process after source change event received.

[Ming Qian]

client need to resume the decoding process
after it dequeues the source change event.
no matter what's the return value of v4l2_resolution_changed().
if the client doesn't resume the decoding process,
the decoder may keep waiting

in documentation of v4l2 stateful decoder, we can see the following
description:
	The client must continue the sequence as described below to
	continue the decoding process.
	1.  Dequeue the source change event.
		Important
		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.
	2.  Continue with the Capture Setup sequence.

Signed-off-by: Ming Qian <ming.qian at nxp.com>
---
 libavcodec/v4l2_context.c | 52 ++++++++++++++++++++++++---------------
 1 file changed, 32 insertions(+), 20 deletions(-)

diff --git a/libavcodec/v4l2_context.c b/libavcodec/v4l2_context.c
index dda5157698c3..b08f0015c2e5 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
@@ -163,7 +178,7 @@ static int v4l2_handle_event(V4L2Context *ctx)
     V4L2m2mContext *s = ctx_to_m2mctx(ctx);
     struct v4l2_format cap_fmt = s->capture.format;
     struct v4l2_event evt = { 0 };
-    int reinit, ret;
+    int ret;
 
     ret = ioctl(s->fd, VIDIOC_DQEVENT, &evt);
     if (ret < 0) {
@@ -185,35 +200,29 @@ static int v4l2_handle_event(V4L2Context *ctx)
         return 0;
     }
 
-    reinit = v4l2_resolution_changed(&s->capture, &cap_fmt);
-    if (reinit) {
+    if (v4l2_resolution_changed(&s->capture, &cap_fmt)) {
         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)
-        s->reinit = 1;
+    s->reinit = 1;
 
-    if (reinit) {
-        if (s->avctx)
-            ret = ff_set_dimensions(s->avctx, s->capture.width, s->capture.height);
-        if (ret < 0)
-            av_log(logger(ctx), AV_LOG_WARNING, "update avcodec height and width\n");
+    if (s->avctx)
+        ret = ff_set_dimensions(s->avctx, s->capture.width, s->capture.height);
+    if (ret < 0)
+        av_log(logger(ctx), AV_LOG_WARNING, "update avcodec height and width\n");
 
-        ret = ff_v4l2_m2m_codec_reinit(s);
-        if (ret) {
-            av_log(logger(ctx), AV_LOG_ERROR, "v4l2_m2m_codec_reinit\n");
-            return AVERROR(EINVAL);
-        }
-        goto reinit_run;
+    ret = ff_v4l2_m2m_codec_reinit(s);
+    if (ret) {
+        av_log(logger(ctx), AV_LOG_ERROR, "v4l2_m2m_codec_reinit\n");
+        return AVERROR(EINVAL);
     }
 
-    /* dummy event received */
-    return 0;
-
     /* reinit executed */
-reinit_run:
     return 1;
 }
 
@@ -551,6 +560,9 @@ int ff_v4l2_context_set_status(V4L2Context* ctx, uint32_t cmd)
     int type = ctx->type;
     int ret;
 
+    if (ctx->streamon == (cmd == VIDIOC_STREAMON))
+        return 0;
+
     ret = ioctl(ctx_to_m2mctx(ctx)->fd, cmd, &type);
     if (ret < 0)
         return AVERROR(errno);
-- 
2.32.0