I tried playing two flv files with this program and it would only play one of the files. I also tried the "FLVPlayer" from http://streampower.free.fr/ and it also only played one file (the same one.) Neither program supports drag-and-drop and the interface for each is rough at best.

I then discovered that Sorenson Squeeze 4 came with "SorensonFlvPlayer" which played both files and supported drag-and-drop. :)

The file that would NOT play in this program began as follows:
00000000 46 4c 56 01 05 00 00 00 09 00 00 00 00 12 00 00 |FLV.............|
00000010 e0 00 00 00 00 00 00 00 02 00 0a 6f 6e 4d 65 74 |...........onMet|
00000020 61 44 61 74 61 08 00 00 00 0a 00 08 64 75 72 61 |aData.......dura|
00000030 74 69 6f 6e 00 40 33 9e 35 3f 7c ed 92 00 05 77 |tion.@3.5?|....w|
00000040 69 64 74 68 00 40 7c 40 00 00 00 00 00 00 06 68 |idth.@|@.......h|
00000050 65 69 67 68 74 00 40 75 00 00 00 00 00 00 00 0d |eight.@u........|
00000060 76 69 64 65 6f 64 61 74 61 72 61 74 65 00 40 79 |videodatarate.@y|
00000070 00 00 00 00 00 00 00 09 66 72 61 6d 65 72 61 74 |........framerat|
00000080 65 00 40 3d f8 51 00 00 00 00 00 0c 76 69 64 65 |e.@=.Q......vide|
00000090 6f 63 6f 64 65 63 69 64 00 40 10 00 00 00 00 00 |ocodecid.@......|
000000a0 00 00 0d 61 75 64 69 6f 64 61 74 61 72 61 74 65 |...audiodatarate|
000000b0 00 40 58 00 00 00 00 00 00 00 0a 61 75 64 69 6f |.@X........audio|
000000c0 64 65 6c 61 79 00 3f a3 74 bc 6a 7e f9 db 00 0c |delay.?.t.j~....|
000000d0 61 75 64 69 6f 63 6f 64 65 63 69 64 00 40 00 00 |audiocodecid.@..|
000000e0 00 00 00 00 00 00 0c 63 61 6e 53 65 65 6b 54 6f |.......canSeekTo|
000000f0 45 6e 64 01 01 00 00 09 00 00 |End.......|

The file which would play in this program began as follows:
00000000 46 4c 56 01 05 00 00 00 09 00 00 00 00 12 00 01 |FLV.............|
00000010 3e 00 00 00 00 00 00 00 02 00 0a 6f 6e 4d 65 74 |>..........onMet|
00000020 61 44 61 74 61 08 00 00 00 0e 00 08 64 75 72 61 |aData.......dura|
00000030 74 69 6f 6e 00 40 35 8c 08 31 26 e9 79 00 0d 6c |tion.@5..1&.y..l|
00000040 61 73 74 74 69 6d 65 73 74 61 6d 70 00 40 35 8c |asttimestamp.@5.|
00000050 08 31 26 e9 79 00 08 64 61 74 61 73 69 7a 65 00 |.1&.y..datasize.|
00000060 41 38 5e 3f 00 00 00 00 00 0f 6d 65 74 61 64 61 |A8^?......metada|
00000070 74 61 63 72 65 61 74 6f 72 02 00 05 46 6c 69 78 |tacreator...Flix|
00000080 32 00 0c 63 61 6e 53 65 65 6b 54 6f 45 6e 64 00 |2..canSeekToEnd.|
00000090 3f f0 00 00 00 00 00 00 00 0c 76 69 64 65 6f 63 |?.........videoc|
000000a0 6f 64 65 63 69 64 00 40 00 00 00 00 00 00 00 00 |odecid.@........|
000000b0 05 77 69 64 74 68 00 40 74 00 00 00 00 00 00 00 |.width.@t.......|
000000c0 06 68 65 69 67 68 74 00 40 6e 00 00 00 00 00 00 |.height.@n......|
000000d0 00 0d 76 69 64 65 6f 64 61 74 61 72 61 74 65 00 |..videodatarate.|
000000e0 40 80 24 eb f0 5d 56 51 00 09 66 72 61 6d 65 72 |@.$..]VQ..framer|
000000f0 61 74 65 00 40 3d fa ba e7 e0 |ate.@=....|