[FFmpeg-devel] [PATCH] lavd/v4l2: Return FFERROR_REDO 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 FFERROR_REDO instead. I have not seen the
issue appearing twice or more often in a row. It was more like
one single error every two hours.

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

Fixes #4795
---
 libavdevice/v4l2.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavdevice/v4l2.c b/libavdevice/v4l2.c
index 1b9c6e7..5a1b324 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 FFERROR_REDO;
         }
     }

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