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  1. My organization has previously posted video files to Youtube that were split into pieces to fit under the 10 minute limit. Now, we have a new account with the ability to post videos longer than 15 minutes. Since we need to migrate our old videos over to the new account anyway, we figured we may as well combine the split videos into one.

    We don't have access to the original source video files. Downloading them from Youtube via Video DownloadHelper for Firefox (HQ35 quality setting, which is the highest one available for these videos) yields FLV files with the following specs:

    via Media Player Classic Homecinema:
    Video: MPEG4 Video (H264) 608x480 [Video]
    Audio: AAC 44100Hz stereo [Audio]

    via VLC Player:
    Video Codec: H264 - MPEG-4 AVC (part 10) (avc1), Resolution: 600x480, Frame rate: 15
    Audio Codec: MPEG AAC Audio (mp4a), Channels: Stereo, Sample rate: 44100 Hz

    I've been trying to use Avidemux to combine them and spit out MP4 files via the video/audio "Copy" options, but the best results I can get still have noticeable audio sync issues.

    This might be related to the problem: When I load either FLV into Avidemux, I get the message "H.264 detected - If the file is using B-frames as reference it can lead to a crash or stuttering. Avidemux can use another mode which is safe but YOU WILL LOSE FRAME ACCURACY. Do you want to use that mode?" (Yes/No)

    I get the same sync problems no matter which of those options I pick, and even if I just import on of the files into Avidemux and immediately export it without trying to append the other half.

    I also tried saving the combined file in different containers like MKV (same result) and AVI (crashed the player and/or produced stuttering audio).

    Any ideas what might be causing this, and what settings or editing program can solve it? I got the impression from another post on this forum that it might be caused by the original video being variable bitrate, but I'm not sure whether my source videos use that or not.
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  2. I'm a MEGA Super Moderator Baldrick's Avatar
    Join Date: Aug 2000
    Location: Sweden
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    Joining often causes such problems. But try:

    Try join with mp4box / mymp4boxgui to a single mp4.
    Try join the flv to a single mkv with mkvmergegui.
    Try just renconvert the audio part in avidemux, under audio choose aac audio and see if it works any better.


    If that doesn't make any difference then check the flv with mediainfo and see if says anything else for the framerate, like vfr=variable frame rate.
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  3. it's a dumb idea to download them and rejoin them for splitting into larger pieces then to be reuploaded. Why? Because YouTube is just going to reencode them yet again and further degrade them. If you don't have the source material anymore, it's best to leave them as-is.

    And what's with the 608 (or 600)x480 resolution? What did you originally upload? An MPEG? And don't they play in slightly bad aspect ratio? Aren't people slightly tall and thin?
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  4. Thanks Baldrick, reconverting the audio did the trick.

    BTW, I tried joining the FLVs in mkvmergegui, but it said that format isn't supported. Did you have a way to make it handle them?

    manono: The decision to move the files over (which only involved rejoining them, not splitting them back up) was made by others. I was just responsible for the technical side.
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  5. I'm a MEGA Super Moderator Baldrick's Avatar
    Join Date: Aug 2000
    Location: Sweden
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    I was first thinking of mp4 files. I don't think mkvmergegui supports any flv.
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  6. Hoover Fanatic budwzr's Avatar
    Join Date: Apr 2007
    Location: City Of Angels
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    You're gonna need an NLE like Vegas or Premiere.

    You're gonna need to demux everything into single files.

    The files you have from YT are basically "podcasts". Low resolution. You need to upsample and do advanced editing to get them into 720p format.

    If you post a sample here, I'll do a short clip so you have an idea of what to expect. Or there are others here that can do this too.
    Last edited by budwzr; 6th Oct 2011 at 12:51.
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