mail was sent to projects@mplayerhq.hu , so forwarding it here. -- Hello, When I using youtube-dl to download some video from website,I found that When the video file is very large like 4.48GB. RtmpDump will report error "ERROR: Unexpected start of file, error in tag sizes, couldn't arrive at prevTagSize=0" So I download the source file,try and try again finally the project works, and then check and check again ... At last I figure out what's wrong with the program. In the last version seems trying to fix the large file problem using ftello instead of ftell .But the fseek function remains the same ,when execute fseek(file, 0, SEEK_END); size = ftello(file); Actually ftello(file) returns 0 to size.Finally I figure out the bug is that replace all fseek with fseeko to deal with large file problem. Thank you for your team proving this wonderful software stack. //sunsocool //fseek(file, 0, SEEK_END); fseeko(file, 0, SEEK_END); size = ftello(file); //fseek(file, 4, SEEK_SET); fseeko(file, 4, SEEK_SET); ... // go through the file and find the last video keyframe do { int xread; skipkeyframe: if (size - tsize < 13) { RTMP_Log(RTMP_LOGERROR, "Unexpected start of file, error in tag sizes, couldn't arrive at prevTagSize=0 size(%lld) - tsize(%lld)< 13 ", size, tsize); return RD_FAILED; } --