[FFmpeg-devel] [PATCH] libavdevice/v4l2: Return EAGAIN when receiving a frame of unexpected size

[Alexander Strasser]

I had found that when capturing video for some hours from
USB Camera-B4.09.24.1 (Manufacturer: OmniVision Technologies, Inc.),
sometimes when invoking the ioctl DQBUF, the returned buffer is not
filled with the size we expect for the raw video frame.

Here are two examples for such occurrences:

    [video4linux2,v4l2 @ 0x258b440] Dequeued v4l2 buffer contains 609596 bytes, but 614400 were expected. Flags: 0x00000001.
    /dev/video1: Invalid data found when processing input

    [video4linux2,v4l2 @ 0x225f440] Dequeued v4l2 buffer contains 609508 bytes, but 614400 were expected. Flags: 0x00000001.
    /dev/video1: Invalid data found when processing input

The ffmpeg CLI tool will then stop capturing and exit.

To avoid this, return AVERROR(EAGAIN) instead.

While searching for the above quoted error message I found a ticket
that mentions this type of problem on our tracker.

Probably fixes #4795
---

We re-discovered this problem that was reported many years ago, while running
the motion vector demo at Chemnitzer Linux-Tage yesterday and today.

 libavdevice/v4l2.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavdevice/v4l2.c b/libavdevice/v4l2.c
index 1b9c6e7..894692e 100644
--- a/libavdevice/v4l2.c
+++ b/libavdevice/v4l2.c
@@ -542,7 +542,7 @@ static int mmap_read_frame(AVFormatContext *ctx, AVPacket *pkt)
                    "Dequeued v4l2 buffer contains %d bytes, but %d were expected. Flags: 0x%08X.\n",
                    buf.bytesused, s->frame_size, buf.flags);
             enqueue_buffer(s, &buf);
-            return AVERROR_INVALIDDATA;
+            return AVERROR(EAGAIN);
         }
     }
 
--