[FFmpeg-devel] [PATCH 2/2] dshow: handle events in graph

Don Moir donmoir at comcast.net
Thu Dec 6 02:54:41 CET 2012

> From: "Ramiro Polla" <ramiro.polla at gmail.com>
> To: "FFmpeg development discussions and patches" <ffmpeg-devel at ffmpeg.org>
> Sent: Tuesday, December 04, 2012 1:23 AM
> Subject: [FFmpeg-devel] [PATCH 2/2] dshow: handle events in graph
>> Hi,
>> Thanks to Don Moir for pointing out the problem and providing a fix.
>> Don, could you please test that this patch fixes the problem for you?
>> Ramiro
> Ramiro, your patch sort of works but had a couple bugs.
> o - fixes return value in dshow_read_header. Your patch for this had a couple misplaced ')' in it.
> o - re-added ctx->eof. After the device has failed, this is a check to stop trying to read any more packets in dshow_read_packet.
> Without this check and someone calls av_read_frame after it has already failed will result in a hang.
> o - dshow_check_event_queue did not free the event when eof was detected. I modified it to take the ctx struct instead of media
> event so that ctx->eof could be set.
> o - added CoUninitialize to dshow_read_close. Every call to CoInitialize should have a matching CoUnititalize. Changed the 
> position
> of CoInitialize in dshow_read_header so we always know to call CoUnintialize without flagging it.
> With event handling added to dshow.c and fix for ret value in dshow_read_header I can't get any abnormal behavior like hangs.
> Without the changes I can get to fail in at least 3 different ways.
> I will be working in the area of camera support for awhile and will continue to test. So if any kind of modifications to dshow
> support or device listing is wanted, now would be a good time for them.
> Ramiro, please review the attached modified dshow.c
> Don

Attached dshow.c and dshow.diff.  diff is from current dshow.c and attached dshow.c

Had to move the position of ICreateDevEnum_Release in  dshow_read_header since on error dshow_read_close is called which now calls 

static int dshow_read_header(AVFormatContext *avctx)

-    if (ret < 0)
-        dshow_read_close(avctx);
-    if (devenum)
-        ICreateDevEnum_Release(devenum);
+    if (devenum)
+        ICreateDevEnum_Release(devenum);
+    if (ret < 0)
+        dshow_read_close(avctx);
    return ret;
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