I'm not sure where to post about this because it's an issue with the program itself, not really a tech support thing. This is the best spot I've found, so here goes.
OBS suggests that you capture your recordings with a file format such as .mkv or .flv, in case the program crashes or is unable to process the video- this way it will still be usable if that happens. I've had .mp4 recordings get lost by OBS crashes before, so I do this because it's better to be safe than sorry. .mkv and .flv files are not usable in editing programs like Sony Vegas or Adobe Premiere, so they must first be re-encoded/remuxed to .mp4 or a similar streamable video file format.
OBS offers the option to do this for you and it's very convenient, but for several months now (maybe even years) the remuxing process goes wrong somewhere in the middle and it creates a file with an improper .mp4 container. For some reason, the .mp4 file it creates is incompatible with GPU-accelerated video processing. NVEC, HEVC, and CUDA do not work with the .mp4 files created by OBS and it's been this way across multiple computers, multiple installs of OBS in different environments. There are several threads on the forums about this. This problem can currently be solved by disabling GPU acceleration and rendering using CPU only, but that leads to this:
This video would take less than an hour to render if I were able to use GPU-accelerated rendering, but the file is broken so I cannot. I tried it in both Sony Vegas and Adobe Premiere and ran into the same problem. If I take the source .mkv file and convert it to .mp4 on my own using Handbrake or FFMPEG, it's a much slower process than OBS' own remuxing but this problem does not occur. I'm not really much of a behind-the-scenes guy so I don't know what specifically is causing it, but something about the remuxing process has been broken for a very long time. I would like to see it fixed.
OBS suggests that you capture your recordings with a file format such as .mkv or .flv, in case the program crashes or is unable to process the video- this way it will still be usable if that happens. I've had .mp4 recordings get lost by OBS crashes before, so I do this because it's better to be safe than sorry. .mkv and .flv files are not usable in editing programs like Sony Vegas or Adobe Premiere, so they must first be re-encoded/remuxed to .mp4 or a similar streamable video file format.
OBS offers the option to do this for you and it's very convenient, but for several months now (maybe even years) the remuxing process goes wrong somewhere in the middle and it creates a file with an improper .mp4 container. For some reason, the .mp4 file it creates is incompatible with GPU-accelerated video processing. NVEC, HEVC, and CUDA do not work with the .mp4 files created by OBS and it's been this way across multiple computers, multiple installs of OBS in different environments. There are several threads on the forums about this. This problem can currently be solved by disabling GPU acceleration and rendering using CPU only, but that leads to this:

This video would take less than an hour to render if I were able to use GPU-accelerated rendering, but the file is broken so I cannot. I tried it in both Sony Vegas and Adobe Premiere and ran into the same problem. If I take the source .mkv file and convert it to .mp4 on my own using Handbrake or FFMPEG, it's a much slower process than OBS' own remuxing but this problem does not occur. I'm not really much of a behind-the-scenes guy so I don't know what specifically is causing it, but something about the remuxing process has been broken for a very long time. I would like to see it fixed.