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    <p>I had a similar need recently. I was looking for a way in OpenCV to play a video that was already in memory, but without ever having to write the video file to disk. I found out that the ffmpeg interface already supports this through <code>av_open_input_stream</code>. There is just a little more prep work required compared to the <code>av_open_input_file</code> call used in OpenCV to open a file.</p> <p>Between the following two websites I was able to piece together a working solution using the ffmpeg calls. Please refer to the information on these websites for more details:</p> <p><a href="http://ffmpeg.arrozcru.org/forum/viewtopic.php?f=8&amp;t=1170">http://ffmpeg.arrozcru.org/forum/viewtopic.php?f=8&amp;t=1170</a></p> <p><a href="http://cdry.wordpress.com/2009/09/09/using-custom-io-callbacks-with-ffmpeg/">http://cdry.wordpress.com/2009/09/09/using-custom-io-callbacks-with-ffmpeg/</a></p> <p>To get it working in OpenCV, I ended up adding a new function to the <code>CvCapture_FFMPEG</code> class:</p> <pre><code>virtual bool openBuffer( unsigned char* pBuffer, unsigned int bufLen ); </code></pre> <p>I provided access to it through a new API call in the highgui DLL, similar to <code>cvCreateFileCapture</code>. The new <code>openBuffer</code> function is basically the same as the <code>open( const char* _filename )</code> function with the following difference:</p> <pre><code>err = av_open_input_file(&amp;ic, _filename, NULL, 0, NULL); </code></pre> <p>is replaced by:</p> <pre><code>ic = avformat_alloc_context(); ic-&gt;pb = av_alloc_put_byte(pBuffer, bufLen, 0, pBuffer, read_buffer, NULL, NULL); if(!ic-&gt;pb) { // handle error } // Need to probe buffer for input format unless you already know it AVProbeData probe_data; probe_data.buf_size = (bufLen &lt; 4096) ? bufLen : 4096; probe_data.filename = "stream"; probe_data.buf = (unsigned char *) malloc(probe_data.buf_size); memcpy(probe_data.buf, pBuffer, 4096); AVInputFormat *pAVInputFormat = av_probe_input_format(&amp;probe_data, 1); if(!pAVInputFormat) pAVInputFormat = av_probe_input_format(&amp;probe_data, 0); // cleanup free(probe_data.buf); probe_data.buf = NULL; if(!pAVInputFormat) { // handle error } pAVInputFormat-&gt;flags |= AVFMT_NOFILE; err = av_open_input_stream(&amp;ic , ic-&gt;pb, "stream", pAVInputFormat, NULL); </code></pre> <p>Also, make sure to call <code>av_close_input_stream</code> in the <code>CvCapture_FFMPEG::close()</code> function instead of <code>av_close_input_file</code> in this situation.</p> <p>Now the <code>read_buffer</code> callback function that is passed in to <code>av_alloc_put_byte</code> I defined as:</p> <pre><code>static int read_buffer(void *opaque, uint8_t *buf, int buf_size) { // This function must fill the buffer with data and return number of bytes copied. // opaque is the pointer to private_data in the call to av_alloc_put_byte (4th param) memcpy(buf, opaque, buf_size); return buf_size; } </code></pre> <p>This solution assumes the entire video is contained in a memory buffer and would probably have to be tweaked to work with streaming data.</p> <p>So that's it! Btw, I'm using OpenCV version 2.1 so YMMV.</p>
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    1. POprocess video stream from memory buffer
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    1. COI had solved this but forgot to post my solution. This is indeed how I did it.
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    2. COa couple notes: `memcpy(probe_data.buf, data, 4096)` should use probe_data.buf_size not 4096 (or it will crash for inputs smaller than 4096). `av_alloc_put_byte` has been renamed to `avio_alloc_context`
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