[Libav-user] custom av_log callback receiving incorrect format specifiers from h264 module

[Blake Senftner]

Adding a string replace from “%td” to “%d” on the fmt string enables logging without issue, btw. 

Sincerely,
-Blake Senftner

> On Dec 18, 2016, at 7:28 AM, Blake Senftner <bsenftner at earthlink.net> wrote:
> 
> Hello,
> 
> I am working with ffmpeg libav* 3.2 libs, downloaded pre-built from Zeranoe early November, my versions are:
> 
> libavutil      55. 34.100 / 55. 34.100
> libavcodec     57. 64.100 / 57. 64.100
> libavformat    57. 56.100 / 57. 56.100
> libavdevice    57.  1.100 / 57.  1.100
> libavfilter     6. 65.100 /  6. 65.100
> libswscale      4.  2.100 /  4.  2.100
> libswresample   2.  3.100 /  2.  3.100
> libpostproc    54.  1.100 / 54.  1.100
> 
> I’m developing a video playback library, (no audio handling.) I started with the Dranger tutorials, but have updated everything to the latest APIs from reading here, and other sources. So far the code is having no problems playing live USB video, or any video file I can find, but does not play IP cameras delivering rtsp h264 streams correctly. The non-keyframes are very blurry. Plus, for media files as well as rtsp streams, I can only get half speed or lower playback.
> 
> I’ll be posting a few questions about those issues later, but first I want to ask about my implementation of an av_log callback, as I am getting crashes from an “incorrect format specifier” delivered from the “h264” module. The specific format string causing the crash is “error while decoding MB %d %d, bytestream %td\n”. (Is the “t” size modifier valid in Visual Studio?)
> 
> void CE_LIBAV_Video::logging_callback(void *ptr, int level, const char *fmt, va_list vargs)
> {
> 	static char message[8192];		
> 	const char *module = NULL;
> 
> 	if (level > AV_LOG_WARNING)
> 		return;
> 
> 	 // Get module name
> 	 if (ptr)
> 	 {
> 		AVClass *avc = *(AVClass**) ptr;
> 		module = avc->item_name(ptr);
> 	 }
> 
> 	 // Create the actual message
> 	 vsnprintf_s(message, sizeof(message), _TRUNCATE, fmt, vargs);
> 
> 	 ofstream log_file;
> 	 log_file.open( "libav.log", std::ios::app );
> 	 log_file << message;
> 	 log_file.close();
> }
> 
> Playing USB video, I see no av_log format specifier issues. Playing media files, non-h264, I see no av_log issues, but when playing an h264 video file I also see the same format specifier issue. 
> 
> I’m working in Win10, Visual Studio 2013 Community. 
> 
> Sincerely,
> -Blake Senftner
> Mad Computer Scientist 
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