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  1. Member
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    I recently captured a 3 hour VHS tape in 30 min increments using Lagarith and want to merge the files together and save in Lagarith format for archiving.

    I tested merging using with VirtualDub2 and Avidemux but both have given me different sized videos.

    For VirtualDub2, my method was to append them and cut out any over lapping scenes. I used "Direct Stream Copy" for the video and audio as I didn't want to re-encode and then I saved the compiled video in Lagarith format.

    For Avidemux, I selected "Copy" for video and audio, appended each clip, cut out overlapping scenes and saved in avi container.

    The resulting file Vdub 2 produced is 03:03:41 long and 80.6 GB (86,616,642,958 bytes).

    General
    Complete name : D:\Video Captures\Live Aid\Panasonic Lag\pan tape 1 bright 127 cont 27 FINAL\Tape 1 Merged.avi
    Format : AVI
    Format/Info : Audio Video Interleave
    Format profile : OpenDML
    File size : 80.7 GiB
    Duration : 3 h 3 min
    Overall bit rate : 62.9 Mb/s
    Writing library : VirtualDub2 build 44282/release

    Video
    ID : 0
    Format : Lagarith
    Codec ID : LAGS
    Duration : 3 h 3 min
    Bit rate : 61.3 Mb/s
    Width : 720 pixels
    Height : 576 pixels
    Display aspect ratio : 5:4
    Frame rate : 25.000 FPS
    Standard : PAL
    Color space : YUV
    Chroma subsampling : 4:2:2
    Bit depth : 8 bits
    Bits/(Pixel*Frame) : 5.915
    Stream size : 78.7 GiB (98%)

    Audio
    ID : 1
    Format : PCM
    Format settings : Little / Signed
    Codec ID : 1
    Duration : 3 h 3 min
    Bit rate mode : Constant
    Bit rate : 1 536 kb/s
    Channel(s) : 2 channels
    Sampling rate : 48.0 kHz
    Bit depth : 16 bits
    Stream size : 1.97 GiB (2%)
    Alignment : Aligned on interleaves
    Interleave, duration : 40 ms (1.00 video frame)
    Interleave, preload duration : 500 ms

    The Avidemux video is 03:03:38 and 80.1 GB (86,112,507,668 bytes).

    General
    Complete name : D:\Video Captures\Live Aid\Panasonic Lag\pan tape 1 bright 127 cont 27 FINAL\Tape 1 Merged avidemux lag.avi
    Format : AVI
    Format/Info : Audio Video Interleave
    Format profile : OpenDML
    File size : 80.2 GiB
    Duration : 3 h 3 min
    Overall bit rate : 62.5 Mb/s

    Video
    ID : 0
    Format : Lagarith
    Codec ID : LAGS
    Duration : 3 h 3 min
    Bit rate : 61.0 Mb/s
    Width : 720 pixels
    Height : 576 pixels
    Display aspect ratio : 5:4
    Frame rate : 25.000 FPS
    Standard : PAL
    Color space : YUV
    Chroma subsampling : 4:2:2
    Bit depth : 8 bits
    Bits/(Pixel*Frame) : 5.881
    Stream size : 78.2 GiB (98%)

    Audio
    ID : 1
    Format : PCM
    Format settings : Little / Signed
    Codec ID : 1
    Duration : 3 h 3 min
    Bit rate mode : Constant
    Bit rate : 1 536 kb/s
    Channel(s) : 2 channels
    Sampling rate : 48.0 kHz
    Bit depth : 16 bits
    Stream size : 1.97 GiB (2%)
    Alignment : Aligned on interleaves
    Interleave, duration : 25 ms (0.63 video frame)
    As you can see, the two videos seem to have the same properties aside from "Bits/(Pixel*Frame)".

    1. Is my method for merging the videos in VDub2 correct? There's also the option for "Fast Re-compress" but I wasn't sure if I should use that or Direct Stream Copy. My goal is to have no re-compression and loss of quality.

    2. Can anyone explain why the VDub 2 produced video is 700 mb larger than the AVIdemux video? It can't be simply because its 3 seconds longer. I assume I've messed up the merging some how...?

    Thank you!
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  2. Member DB83's Avatar
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    Well the bitrate for the former is slightly bigger than the latter. So that, 3 secs aside, accounts for the variance in file size.


    Now vdub2 has, IIRC, its own built-in Lagarith codec. But you can also select the stand-alone that avidemux would rely upon. So that may be a factor.


    I guess you are doing the capture this way since you can not allow for a complete tape capture in one go.
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  3. Even if the video streams were exactly the same you would expect different file sizes because different muxers have different overhead. Some will alighn frames to start on 512 byte (or 1024 byte, or some other value) boundaries so there will be different padding. Different metadata may be included. Etc.
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    Thank you for the replies!

    Yes, I captured the video as Lagarith in 30 min blocks as I cannot capture it in one go. I want to compile the videos together into one 3 hour block.

    Am I correct in thinking that by using "Direct Stream Copy", the video won't be re-encoded? I ask because I read that the video should save very quickly when using this option, but it still took around 90 mins. But maybe that's because the video is 3 hours long...?

    Just out of curiosity, if I was to choose "Full Processing Mode" and choose Lagarith from the list of codecs and re-encoded the video, would it result in a loss of quality? My background is mostly in audio work. If you capture an LP in .wav format, edit it and save it as a .wav file you don't lose any quality. Can the same logic be applied to capturing, trimming (not applying filters) and saving using Lagarith?

    Finally, am I right in assuming that there will be no difference in quality by VDub2 in "Direct Stream" mode vs Avidemux in "Copy" mode despite the file sizes being different?

    Many thanks for the help!
    Last edited by dave_van_damme; 13th Aug 2021 at 01:26. Reason: grammar
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  5. Member DB83's Avatar
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    Although I do not use direct stream copy (or even deal with 3 hour captures/edits) I just did a quick test.


    A 45 sec Lagarith appeared to take over 20 sec to write so your 90 mins does appear to be typical using vdub2.


    However, running the same test in avidemux the copy was almost instant and did, in fact create a slightly larger file even with a short source.


    No. There should be no quality difference between the two modes.
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  6. Originally Posted by dave_van_damme View Post
    Am I correct in thinking that by using "Direct Stream Copy", the video won't be re-encoded?
    Yes.

    Originally Posted by dave_van_damme View Post
    I ask because I read that the video should save very quickly when using this option, but it still took around 90 mins. But maybe that's because the video is 3 hours long...?
    How long it takes depends on several issues including the size of the file, the speed of your drive(s), whether your input and output are on the same drive or different drive, how recently you accessed the source, etc. If you're remuxing a very large file from hard drive to the same hard drive it's not surprising it takes a long time -- given the large amount of data, the inability of Windows to cache all that data, the large amount of drive seeking on the alternating reads and writes, etc.

    Originally Posted by dave_van_damme View Post
    Just out of curiosity, if I was to choose "Full Processing Mode" and choose Lagarith from the list of codecs and re-encoded the video, would it result in a loss of quality?
    As long as you avoid any pixel format changes. For example, if you convert from incoming Lagarith YUY2 to RGB, back to YUY2, then save as Lagarith again, you will get losses from the color format conversions. Old versions of VirtualDub always converted YUY2 to RGB when using Full Processing Mode (even if not filtering). Newer versions of VirtualDub (and all versions of VirtualDub2) are smarter about that and only converted when filters need RGB.

    Originally Posted by dave_van_damme View Post
    Finally, am I right in assuming that there will be no difference in quality by VDub2 in "Direct Stream" mode vs Avidemux in "Copy" mode despite the file sizes being different?
    Yes.
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    Fantastic - thank you both for taking the time to answer my questions!!
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