Originally committed as revision 25379 to svn://svn.ffmpeg.org/ffmpeg/trunk
/**
* Read one packet and put it in 'pkt'. pts and flags are also
* set. 'av_new_stream' can be called only if the flag
- * AVFMTCTX_NOHEADER is used.
+ * AVFMTCTX_NOHEADER is used and only in the calling thread (not in a
+ * background thread).
* @return 0 on success, < 0 on error.
* When returning an error, pkt must not have been allocated
* or must be freed before returning