>> I have written a patch for FFmpeg that deals with the problem for both
>> devices so it’s not really an issue for me anymore, but I’m not sure
>> if the patch will get accepted in their master git as it’s a little
>> messy.
>
> Please post this patch here!
Here you go, Andrey. This patch basically makes it throw away corrupted buffers and then also the first 8 buffers after the last corrupted buffer.
It’s not sufficient just to throw away the corrupted buffers as I have noticed that the first few legitimate buffers appear at slightly irregular time intervals leading to FFmpeg spewing out a bunch of warnings for the duration of the capture. In my tests around 3 buffers have to be ignored but I’ve fixed it at 8 to be on the safe side. It’s a bit ugly though, to be honest, I don’t know how the number of buffers that need to be ignored would depend on the framerate, video size etc, but it works for my 1080i test.
With this patch, you get some warnings at the start, for both devices, as it encounters (and recovers from) the corrupted buffers but after that the captures work just fine.
diff --git a/libavdevice/v4l2.c b/libavdevice/v4l2.c
old mode 100644
new mode 100755
index ddf331d..7b4a826
--- a/libavdevice/v4l2.c
+++ b/libavdevice/v4l2.c
@@ -79,6 +79,7 @@ struct video_data {
int buffers;
volatile int buffers_queued;
+ int buffers_ignore;
void **buf_start;
unsigned int *buf_len;
char *standard;
@@ -519,7 +520,9 @@ static int mmap_read_frame(AVFormatContext *ctx, AVPacket *pkt)
av_log(ctx, AV_LOG_WARNING,
"Dequeued v4l2 buffer contains corrupted data (%d bytes).\n",
buf.bytesused);
- buf.bytesused = 0;
+ s->buffers_ignore = 8;
+ enqueue_buffer(s, &buf);
+ return FFERROR_REDO;
} else
#endif
{
@@ -529,14 +532,28 @@ static int mmap_read_frame(AVFormatContext *ctx, AVPacket *pkt)
s->frame_size = buf.bytesused;
if (s->frame_size > 0 && buf.bytesused != s->frame_size) {
- av_log(ctx, AV_LOG_ERROR,
+ av_log(ctx, AV_LOG_WARNING,
"Dequeued v4l2 buffer contains %d bytes, but %d were expected. Flags: 0x%08X.\n",
buf.bytesused, s->frame_size, buf.flags);
+ s->buffers_ignore = 8;
enqueue_buffer(s, &buf);
- return AVERROR_INVALIDDATA;
+ return FFERROR_REDO;
}
}
+
+ /* if we just encounted some corrupted buffers then we ignore the next few
+ * legitimate buffers because they can arrive at irregular intervals, causing
+ * the timestamps of the input and output streams to be out-of-sync and FFmpeg
+ * to continually emit warnings. */
+ if (s->buffers_ignore) {
+ av_log(ctx, AV_LOG_WARNING,
+ "Ignoring dequeued v4l2 buffer due to earlier corruption.\n");
+ s->buffers_ignore --;
+ enqueue_buffer(s, &buf);
+ return FFERROR_REDO;
+ }
+
/* Image is at s->buff_start[buf.index] */
if (avpriv_atomic_int_get(&s->buffers_queued) == FFMAX(s->buffers / 8, 1)) {
/* when we start getting low on queued buffers, fall back on copying data */
@@ -608,6 +625,7 @@ static int mmap_start(AVFormatContext *ctx)
}
}
s->buffers_queued = s->buffers;
+ s->buffers_ignore = 0;
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (v4l2_ioctl(s->fd, VIDIOC_STREAMON, &type) < 0) {
--
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