On Fri, 21 Jul 2023, Richard Acayan wrote:
Will this patch be applied or receive any comments? I have been waiting
more than 2 weeks since the original submission
(https://ffmpeg.org/pipermail/ffmpeg-devel/2023-July/311580.html) and
have not received a response since.
I am trying to get mpv to work again with the v4l2_m2m codec, as it
started emitting segmentation faults. This is partly due to some
incorrect usage of libavcodec in mpv, and partly due to the
error/warning handling in libavcodec. An mpv maintainer dismissed this
as a bug in ffmpeg, and this change is simpler than what mpv would need
for a fix, so I am hoping that this patch goes in.
I don't have write access so I can't apply it myself, even if there are
no objections.
On Tue, Jul 18, 2023 at 06:00:17PM -0400, Richard Acayan wrote:
The error handler for POLLERRs assumes that the timeout is only zero
when v4l2_dequeue_v4l2buf is called by v4l2_getfree_v4l2buf. This
assumption is incorrect, as ff_v4l2_context_dequeue_frame also calls
this function with a timeout of zero. Do not check for unavailable
buffers if the buffers are uninitialized.
See https://trac.ffmpeg.org/ticket/9957 for the original bug report.
Signed-off-by: Richard Acayan <mailingrad...@gmail.com>
---
libavcodec/v4l2_context.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/libavcodec/v4l2_context.c b/libavcodec/v4l2_context.c
index a40be94690..69ddf80723 100644
--- a/libavcodec/v4l2_context.c
+++ b/libavcodec/v4l2_context.c
@@ -327,7 +327,7 @@ start:
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 (timeout == 0) {
+ if (timeout == 0 && ctx->buffers) {
This would warn if no buffers are allocated yet, but this is not a warning
condition as far as I understand the issue, simply a different API usage
pattern. So maybe it is better to simply do a
if (!ctx->buffers)
return NULL;
in the beginning of the if (timeout == 0) block.
Thanks,
Marton
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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