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Do you have any advice for digitizing VHS tapes?
(sh.itjust.works)
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this post was submitted on 10 Sep 2024
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Ha, honestly, I wish that I would've done this to begin with. It's way cheaper, and simpler to get the one composite capture card rather than converting composite to HDMI, then capturing HDMI. I'm honestly not entirely sure why I did the latter — perhaps it's because I was under some presumption that such a device wouldn't exist (which, now, I realize is an obviously silly assumption to make). I found this one. It's still just a generic capture card, but it's a direct composite capture. Do you think that it would suffice?
Hmmm... It seems to be an EasyCAP clone, there are several devices in this form factor with different chipsets. As far as I've looked, they all will stream lossless interlaced video and it's up to you how to handle it. The "720p" claim in the listing is likely bogus - the seller just misread the actual spec, which is 720x480i for NTSC and 720x576i for PAL. The last time I was capturing video, I used the VirtualDub software, which can store the raw capture in HuffYUV, however OBS can also capture interlaced video with decent compression. This capture device seems to be labeled as "BR116" based on photos in reviews, which can help identifying the chipset. BR116 is sold by Conrad and its manual by them mentions "STK1160" in a screenshot, so this Amazon one most likely also uses the STK1160 chip, which was one of the worst ones in this timebase stability test (which means it has no TBC). However, it's alright if your VCR is a late model that already does TBC internally.
Good to know! That link has a lot of good information.
Noted! I will keep this in mind.
I came across this video about digitizing VHS tapes [1]. It talks about hardware to use, and hardware to avoid [1.6]. One of the examples that it gives for hardware to avoid seems to be a clone of the device that I was looking at on Amazon [1.2]. The rationale for why it should be avoided was that it doesn't pass both fields of the interlaced video through independently [1.1]. Though, you have mentioned that it's fine to capture the video interlaced, so perhaps this isn't a big deal-breaker. The capture cards that the video recommends are:
References
So, uh... The EasyCAP device passes both fields into your PC but the video says that the driver does not interpret them correctly and uses probably the most common, incorrect deinterlacing method (see earlier comment with the method list). It is technically possible to reinterlace the video but I haven't needed to do that, and you should do so before any lossy encoding to a file. I assume the community-written Linux driver has no such issue.
The tutorial is mostly correct for people who want to create YouTube uploads with just one program (for YouTube, progressive video is required and the 480p stream cannot be 60 fps and has a terrible bitrate (and 576p for PAL is not available AT ALL so 1080p60 makes sense) but I strongly recommend not deinterlacing nor scaling in OBS, you can do that later. Record 480i (interlaced) files at very high bitrate and perform the deinterlacing in post.
So, I bought an EasyCap device and ran some tests. I encountered a few things that I don't quite understand, and I would really appreciate your input!
I used a test VHS tape that I purchased at a thrift store (I'm not 100% sure if it's NTSC or PAL, but I'm decently confident that it's NTSC) (I'm also not sure what its aspect ratio is — I think it's either 1.33:1 or 4:3). I'm playing the tape in a PV-D4745S-K VCR. I have the composite out of the VCR going into the aforementioned capture device which is connected to a computer running Arch Linux.
First, I used the following ffmpeg capture settings:
After capturing a short snippet of the test tape, I probed its metadata with
ffprobe -i out.mkv, and saw that it was strangely in 25FPS, and 720x576 (which caused the video to be stretched vertically slightly), which is PAL. So, somehow the NTSC VHS being played in an NTSC VCR was being converted to PAL. In addition to that, the colors in the video were very overexposed. I tried a bunch of different manual settings like specifying interlacing with-vf "interlace",-standard ntsc,-vf scale=720:480,-vf fps=29.97,-standard NTSC, and none of them solved the issue. I then came across this answer on StackOverflow which stated that capture cards themselves have settings for the video feed, and ffmpeg can modify them with the-show_video_device_dialog trueoption. From the ffmpeg documentation:Unfortunately, when trying this option, an error popped up saying that the option was unrecognized. After some digging, and prompting ChatGPT, I found that apparently that option is Windows only as it relies on Windows' "DirectShow system". The way to modify it in Linux is to use the Video4Linux2 framework, which is controlled with
v4l2-ctl. So, I ran the following:which showed the following entry:
So it is able to output NTSC — ie 720x480 at 29.97fps (I guess it rounds up the fps for whatever reason). So I then tried
and it was able to output the video at 720x480 29.97 fps as desired, and the colors were no longer super overexposed. Using the
-vf "interlace"flag, I do seem to also be able to capture interlaced video, so it also doesn't force progressive which is nice.I thought that the capture card would be able to just autodetect what the input resolution was to allow ffmpeg to record at that, or at the very least, I would expect that specifying NTSC in ffmpeg would force the standard, but neither of those worked and I'm not sure why. There's also still an ongoing issue of the video being zoomed in/cropped slightly (I verified this by comparing against online sources of the same video (some were a VHS rip, others from non-VHS sources)). I tested the VCR's output on a regular TV, but unfortunately the TV forced 4:3 and cropped it even more, so I wasn't able to make a perfect comparison, though that was only additional horizontal cropping — the vertical cropping from before was still present. To be able to verify that, I'll have to pick up another test VHS tape to see if perhaps the test VHS tape that I currently have was just recorded in a cropped format.
With the
interlacefilter, make sure you get the field order right. I used not to be so familiar withffmpegand I ended up using some GUI program I can't remember back in the day. See if the driver has an option for no deinterlacing because that happens at driver level.There is no difference between 1⅓:1 and 4:3, they're just different representations of the same thing. Rounding the ratio to 1.33 produces a negligible difference but I would stick with 4:3 for a simpler pixel aspect ratio of 9:8 (1.125} as opposed to 150:133 (1.12782), assuming the capture is 720x480i60.
As for the zoom, TVs will have some overscan because different equipment caused various borders but the capture card should capture all 480 lines. You can check that the output is not vertically scaled by taking a snapshot in a high-movement scene (beware that most image formats are limited to square pixels so better force a PAR of 1:1 for this purpose) and observing if the interlacing indeed causes 1:1 combing as expected. Checking for horizontal crop can be done with another video source (camera, DVD player, STB, game console) generating a test pattern or at least a known image. However, if the vertical scale is correct and the content aspect ratio looks subjectively fine at 4:3 SAR, the crop is most likely OK.