Years ago I asked this question on: stackoverflow about correct syntax using the ffmpeg Concat demuxer to join mp4 files together. One question I hadn't thought to ask at the time was, when joining mp4s that have been encoded by ffmpeg with -movflags +faststart what happens to each joined file's moov atom? Is there only one now? Is the moov still at the top?
Ex: file1.mp4 and file2.mp4 both encoded with ffmpeg using -movflags +faststart and then are joined together using ffmpeg concat demuxer to create all.mp4
I did some investigative work but I'm not very knowledgeable and wanted a definite answer rather than my own assumption. Using the example above I compared the output for "file1.mp4" using atomic parsley and compared it to the output of "all.mp4" and it appears to me that the .moov atom is not in the "faststart" position.
file1.mp4 output
Atom ftyp @ 0 of size: 32, ends @ 32
Atom moov @ 32 of size: 8067606, ends @ 8067638
Atom mvhd @ 40 of size: 108, ends @ 148
Atom trak @ 148 of size: 5898695, ends @ 5898843
Atom tkhd @ 156 of size: 92, ends @ 248
Atom edts @ 248 of size: 36, ends @ 284
Atom elst @ 256 of size: 28, ends @ 284
Atom mdia @ 284 of size: 5898559, ends @ 5898843
Atom mdhd @ 292 of size: 32, ends @ 324
Atom hdlr @ 324 of size: 45, ends @ 369
Atom minf @ 369 of size: 5898474, ends @ 5898843
Atom vmhd @ 377 of size: 20, ends @ 397
Atom dinf @ 397 of size: 36, ends @ 433
Atom dref @ 405 of size: 28, ends @ 433
Atom stbl @ 433 of size: 5898410, ends @ 5898843
Atom stsd @ 441 of size: 150, ends @ 591
Atom avc1 @ 457 of size: 134, ends @ 591
Atom avcC @ 543 of size: 48, ends @ 591
Atom stts @ 591 of size: 24, ends @ 615
Atom stss @ 615 of size: 5584, ends @ 6199
Atom ctts @ 6199 of size: 2502720, ends @ 2508919
Atom stsc @ 2508919 of size: 1047220, ends @ 3556139
Atom stsz @ 3556139 of size: 1258620, ends @ 4814759
Atom stco @ 4814759 of size: 1084084, ends @ 5898843
Atom trak @ 5898843 of size: 2168697, ends @ 8067540
Atom tkhd @ 5898851 of size: 92, ends @ 5898943
Atom edts @ 5898943 of size: 36, ends @ 5898979
Atom elst @ 5898951 of size: 28, ends @ 5898979
Atom mdia @ 5898979 of size: 2168561, ends @ 8067540
Atom mdhd @ 5898987 of size: 32, ends @ 5899019
Atom hdlr @ 5899019 of size: 45, ends @ 5899064
Atom minf @ 5899064 of size: 2168476, ends @ 8067540
Atom smhd @ 5899072 of size: 16, ends @ 5899088
Atom dinf @ 5899088 of size: 36, ends @ 5899124
Atom dref @ 5899096 of size: 28, ends @ 5899124
Atom stbl @ 5899124 of size: 2168416, ends @ 8067540
Atom stsd @ 5899132 of size: 106, ends @ 5899238
Atom mp4a @ 5899148 of size: 90, ends @ 5899238
Atom esds @ 5899184 of size: 54, ends @ 5899238
Atom stts @ 5899238 of size: 32, ends @ 5899270
Atom stsc @ 5899270 of size: 40, ends @ 5899310
Atom stsz @ 5899310 of size: 1084092, ends @ 6983402
Atom stco @ 6983402 of size: 1084084, ends @ 8067486
Atom sgpd @ 8067486 of size: 26, ends @ 8067512 ~
Atom sbgp @ 8067512 of size: 28, ends @ 8067540
Atom udta @ 8067540 of size: 98, ends @ 8067638
Atom meta @ 8067548 of size: 90, ends @ 8067638
Atom hdlr @ 8067560 of size: 33, ends @ 8067593
Atom ilst @ 8067593 of size: 45, ends @ 8067638
Atom ©too @ 8067601 of size: 37, ends @ 8067638
Atom data @ 8067609 of size: 29, ends @ 8067638
Atom free @ 8067638 of size: 8, ends @ 8067646
Atom mdat @ 8067646 of size: 403164726, ends @ 411232372
all.mp4 output
Atom ftyp @ 0 of size: 32, ends @ 32
Atom free @ 32 of size: 8, ends @ 40
Atom mdat @ 40 of size: 197417544, ends @ 197417584
Atom moov @ 197417584 of size: 5203090, ends @ 202620674
Atom mvhd @ 197417592 of size: 108, ends @ 197417700
Atom trak @ 197417700 of size: 3803979, ends @ 201221679
Atom tkhd @ 197417708 of size: 92, ends @ 197417800
Atom edts @ 197417800 of size: 48, ends @ 197417848
Atom elst @ 197417808 of size: 40, ends @ 197417848
Atom mdia @ 197417848 of size: 3803831, ends @ 201221679
Atom mdhd @ 197417856 of size: 32, ends @ 197417888
Atom hdlr @ 197417888 of size: 45, ends @ 197417933
Atom minf @ 197417933 of size: 3803746, ends @ 201221679
Atom vmhd @ 197417941 of size: 20, ends @ 197417961
Atom dinf @ 197417961 of size: 36, ends @ 197417997
Atom dref @ 197417969 of size: 28, ends @ 197417997
Atom stbl @ 197417997 of size: 3803682, ends @ 201221679
Atom stsd @ 197418005 of size: 150, ends @ 197418155
Atom avc1 @ 197418021 of size: 134, ends @ 197418155
Atom avcC @ 197418107 of size: 48, ends @ 197418155
Atom stts @ 197418155 of size: 104, ends @ 197418259
Atom stss @ 197418259 of size: 3464, ends @ 197421723
Atom ctts @ 197421723 of size: 1613944, ends @ 199035667
Atom stsc @ 199035667 of size: 675328, ends @ 199710995
Atom stsz @ 199710995 of size: 811620, ends @ 200522615
Atom stco @ 200522615 of size: 699064, ends @ 201221679
Atom trak @ 201221679 of size: 1398897, ends @ 202620576
Atom tkhd @ 201221687 of size: 92, ends @ 201221779
Atom edts @ 201221779 of size: 36, ends @ 201221815
Atom elst @ 201221787 of size: 28, ends @ 201221815
Atom mdia @ 201221815 of size: 1398761, ends @ 202620576
Atom mdhd @ 201221823 of size: 32, ends @ 201221855
Atom hdlr @ 201221855 of size: 45, ends @ 201221900
Atom minf @ 201221900 of size: 1398676, ends @ 202620576
Atom smhd @ 201221908 of size: 16, ends @ 201221924
Atom dinf @ 201221924 of size: 36, ends @ 201221960
Atom dref @ 201221932 of size: 28, ends @ 201221960
Atom stbl @ 201221960 of size: 1398616, ends @ 202620576
Atom stsd @ 201221968 of size: 106, ends @ 201222074
Atom mp4a @ 201221984 of size: 90, ends @ 201222074
Atom esds @ 201222020 of size: 54, ends @ 201222074
Atom stts @ 201222074 of size: 112, ends @ 201222186
Atom stsc @ 201222186 of size: 160, ends @ 201222346
Atom stsz @ 201222346 of size: 699112, ends @ 201921458
Atom stco @ 201921458 of size: 699064, ends @ 202620522
Atom sgpd @ 202620522 of size: 26, ends @ 202620548 ~
Atom sbgp @ 202620548 of size: 28, ends @ 202620576
Atom udta @ 202620576 of size: 98, ends @ 202620674
Atom meta @ 202620584 of size: 90, ends @ 202620674
Atom hdlr @ 202620596 of size: 33, ends @ 202620629
Atom ilst @ 202620629 of size: 45, ends @ 202620674
Atom ©too @ 202620637 of size: 37, ends @ 202620674
Atom data @ 202620645 of size: 29, ends @ 202620674
Can anyone with moov knowledge prove my assumption right or wrong? If I'm right and ffmpeg concat does not automatically assume to move the moov atom to the top should I change my approach and add -movflags +faststart to the concat demuxer command?
