Q:

FFMPEG error with avformat_open_input returning -135

I have a DLL one of my applications uses to receive video from RTSP cameras.   Under the hood, the DLL uses FFMPEG libs from this release zip :
ffmpeg-20141022-git-6dc99fd-win64-shared.7z

We have a wide variety of cameras in house and most of them work just fine.   However, on one particular Pelco Model Number: IXE20DN-OCP, I am unable to connect.   I tested the camera and rtsp connection string on VLC and it connects to the camera just fine.
I found the connection string here : http://www.ispyconnect.com/man.aspx?n=Pelco
rtsp://IPADDRESS:554/1/stream1

Oddly, even if I leave the port off of VLC, it connects, so I'm guessing its the default RTSP port or that VLC tries a variety of things based on your input.
In any case, when I attempt to connect, I get an error from av_format_open_input.   It returns a code of -135.    When I looked in the error code list I didn't see that listed.   For good measure, I printed out all the errors in error.h just to see what their values were.
DumpErrorCodes - Error Code : AVERROR_BSF_NOT_FOUND = -1179861752
DumpErrorCodes - Error Code : AVERROR_BUG = -558323010
DumpErrorCodes - Error Code : AVERROR_BUFFER_TOO_SMALL = -1397118274
DumpErrorCodes - Error Code : AVERROR_DECODER_NOT_FOUND = -1128613112
DumpErrorCodes - Error Code : AVERROR_DEMUXER_NOT_FOUND = -1296385272
DumpErrorCodes - Error Code : AVERROR_ENCODER_NOT_FOUND = -1129203192
DumpErrorCodes - Error Code : AVERROR_EOF = -541478725
DumpErrorCodes - Error Code : AVERROR_EXIT = -1414092869
DumpErrorCodes - Error Code : AVERROR_EXTERNAL = -542398533
DumpErrorCodes - Error Code : AVERROR_FILTER_NOT_FOUND = -1279870712
DumpErrorCodes - Error Code : AVERROR_INVALIDDATA = -1094995529
DumpErrorCodes - Error Code : AVERROR_MUXER_NOT_FOUND = -1481985528
DumpErrorCodes - Error Code : AVERROR_OPTION_NOT_FOUND = -1414549496
DumpErrorCodes - Error Code : AVERROR_PATCHWELCOME = -1163346256
DumpErrorCodes - Error Code : AVERROR_PROTOCOL_NOT_FOUND = -1330794744
DumpErrorCodes - Error Code : AVERROR_STREAM_NOT_FOUND = -1381258232
DumpErrorCodes - Error Code : AVERROR_BUG2 = -541545794
DumpErrorCodes - Error Code : AVERROR_UNKNOWN = -1313558101
DumpErrorCodes - Error Code : AVERROR_EXPERIMENTAL = -733130664
DumpErrorCodes - Error Code : AVERROR_INPUT_CHANGED = -1668179713
DumpErrorCodes - Error Code : AVERROR_OUTPUT_CHANGED = -1668179714
DumpErrorCodes - Error Code : AVERROR_HTTP_BAD_REQUEST = -808465656
DumpErrorCodes - Error Code : AVERROR_HTTP_UNAUTHORIZED = -825242872
DumpErrorCodes - Error Code : AVERROR_HTTP_FORBIDDEN = -858797304
DumpErrorCodes - Error Code : AVERROR_HTTP_NOT_FOUND = -875574520
DumpErrorCodes - Error Code : AVERROR_HTTP_OTHER_4XX = -1482175736
DumpErrorCodes - Error Code : AVERROR_HTTP_SERVER_ERROR = -1482175992

Nothing even close to -135.   I did find this error, sort of on stack overflow, here runtime error when linking ffmpeg libraries in qt creator where the author claims it is a DLL loading problem error.    I'm not sure what led him to think that, but I followed the advice and used the dependency walker (http://www.dependencywalker.com/) to checkout what dependencies it thought my DLL needed.   It listed a few, but they were already provided in my install package.
To make sure it was picking them up, I manually removed them from the install and observed a radical change in program behavior(that being my DLL didn't load and start to run at all).
So, I've got a bit of init code :
void FfmpegInitialize()
{
 av_lockmgr_register(&LockManagerCb);
 av_register_all();
 LOG_DEBUG0("av_register_all returned\n");
}

Then I've got my main open connection routine ...
int RTSPConnect(const char *URL, int width, int height, frameReceived callbackFunction)
{

    int errCode =0;
    if ((errCode = avformat_network_init()) != 0)
    {
        LOG_ERROR1("avformat_network_init returned error code %d\n", errCode);  
    }
    LOG_DEBUG0("avformat_network_init returned\n");
    //Allocate space and setup the the object to be used for storing all info needed for this connection
    fContextReadFrame = avformat_alloc_context(); // free'd in the Close method

    if (fContextReadFrame == 0)
    {
        LOG_ERROR1("Unable to set rtsp_transport options.   Error code = %d\n", errCode);
        return FFMPEG_OPTION_SET_FAILURE;
    }

    LOG_DEBUG1("avformat_alloc_context returned %p\n", fContextReadFrame);

    AVDictionary *opts = 0;
    if ((errCode = av_dict_set(&opts, "rtsp_transport", "tcp", 0)) < 0)
    {
        LOG_ERROR1("Unable to set rtsp_transport options.   Error code = %d\n", errCode);
        return FFMPEG_OPTION_SET_FAILURE;
    }
    LOG_DEBUG1("av_dict_set returned %d\n", errCode);

    //open rtsp
    DumpErrorCodes();
    if ((errCode = avformat_open_input(&fContextReadFrame, URL, NULL, &opts)) < 0)
    {
        LOG_ERROR2("Unable to open avFormat RF inputs.   URL = %s, and Error code = %d\n", URL, errCode);       
        LOG_ERROR2("Error Code %d = %s\n", errCode, errMsg(errCode));       
        // NOTE context is free'd on failure.
        return FFMPEG_FORMAT_OPEN_FAILURE;
    }
...

To be sure I didn't misunderstand the error code I printed the error message from ffmpeg but the error isn't found and my canned error message is returned instead.
My next step was going to be hooking up wireshark on my connection attempt and on the VLC connection attempt and trying to figure out what differences(if any) are causing the problem and what I can do to ffmpeg to make it work.    As I said, I've got a dozen other cameras in house that use RTSP and they work with my DLL.   Some utilize usernames/passwords/etc as well(so I know that isn't the problem).   
Also, my run logs :
FfmpegInitialize - av_register_all returned
Open - Open called.  Pointers valid, passing control.
Rtsp::RtspInterface::Open - Rtsp::RtspInterface::Open called
Rtsp::RtspInterface::Open - VideoSourceString(35) = rtsp://192.168.14.60:554/1/stream1
Rtsp::RtspInterface::Open - Base URL = (192.168.14.60:554/1/stream1)
Rtsp::RtspInterface::Open - Attempting to open (rtsp://192.168.14.60:554/1/stream1) for WxH(320x240) video
RTSPSetFormatH264 - RTSPSetFormatH264
RTSPConnect - Called
LockManagerCb - LockManagerCb invoked for op 1
LockManagerCb - LockManagerCb invoked for op 2
RTSPConnect - avformat_network_init returned
RTSPConnect - avformat_alloc_context returned 019E6000
RTSPConnect - av_dict_set returned 0
DumpErrorCodes - Error Code : AVERROR_BSF_NOT_FOUND = -1179861752
...
DumpErrorCodes - Error Code : AVERROR_HTTP_SERVER_ERROR = -1482175992
RTSPConnect - Unable to open avFormat RF inputs.   URL = rtsp://192.168.14.60:554/1/stream1, and Error code = -135
RTSPConnect - Error Code -135 = No Error Message Available

I'm going to move forward with wireshark but would like to know the origin of the -135 error code from ffmpeg.  When I look at the code if 'ret' is getting set to -135, it must be happening as a result of the return code from a helper method and not directly in the avformat_open_input method.
https://www.ffmpeg.org/doxygen/2.5/libavformat_2utils_8c_source.html#l00398
After upgrading to the latest daily ffmpeg build, I get data on wireshark.   Real Time Streaming Protocol : 
Request: SETUP rtsp://192.168.14.60/stream1/track1 RTSP/1.0\r\n
Method: SETUP
URL: rtsp://192.168.14.60/stream1/track1
Transport: RTP/AVP/TCP;unicast;interleaved=0-1
CSeq: 3\r\n
User-Agent: Lavf56.31.100\r\n
\r\n

The response to that is the first 'error' that I can detect in the initiation.
Response: RTSP/1.0 461 Unsupported Transport\r\n
Status: 461
CSeq: 3\r\n
Date: Sun, Jan 04 1970 16:03:05 GMT\r\n
\r\n

I'm going to guess that... it means the transport we selected was unsupported.   I quick check of the code reveals I picked 'tcp'.   Looking through the reply to the DESCRIBE command, it appears :
Media Protocol: RTP/AVP

Further, when SETUP is issued by ffmpeg, it specifies :
Transport: RTP/AVP/TCP;unicast;interleaved=0-1

I'm going to try, on failure here to pick another transport type and see how that works.   Still don't know where the -135 comes from.

A:

The solution turned out to be that this particular camera didn't support RTSP over TCP transport.   It wanted UDP.   
I updated to code to try TCP and if that failed, to use an alternate set of options for UDP and another call to try an open things up.
if ((errCode = av_dict_set(&opts, "rtsp_transport", "udp", 0)) < 0)

Works like a charm.   Still concerned about the origin of the -135 and -22 error codes which don't appear in the error.h file.   Maybe an ffmpeg bug where a stray error code is allowed through.

