[FFmpeg-devel] [PATCH v2] avcodec/v4l2_context: suppress POLLERR when buffers are uninitialized

[Richard Acayan <mailingradian@gmail.com>]

A POLLERR occurs when libavcodec attempts to dequeue output buffers
before enqueuing capture buffers. This could happen to an application
deciding to send the first coded packet. Suppress these POLLERRs when
the buffers are uninitialized.

See https://trac.ffmpeg.org/ticket/9957 for the original bug report.

Signed-off-by: Richard Acayan <mailingradian@gmail.com>
---
Changes since v1 (20230718220017.3336-1-mailingradian@gmail.com):
 - stopped emitting POLLERR logs for this case (thanks to feedback from
   Marton Balint)

 libavcodec/v4l2_context.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/libavcodec/v4l2_context.c b/libavcodec/v4l2_context.c
index a40be94690..f20f713e1d 100644
--- a/libavcodec/v4l2_context.c
+++ b/libavcodec/v4l2_context.c
@@ -325,9 +325,13 @@ start:
 
     /* 0. handle errors */
     if (pfd.revents & POLLERR) {
-        /* if we are trying to get free buffers but none have been queued yet
-           no need to raise a warning */
+        /* if we are trying to get free buffers but none have been queued yet,
+         * or if no buffers have been allocated yet, no need to raise a warning
+         */
         if (timeout == 0) {
+            if (!ctx->buffers)
+                return NULL;
+
             for (i = 0; i < ctx->num_buffers; i++) {
                 if (ctx->buffers[i].status != V4L2BUF_AVAILABLE)
                     av_log(logger(ctx), AV_LOG_WARNING, "%s POLLERR\n", ctx->name);
-- 
2.41.0

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