Recording two simultaneous video streams - possible?

[thender]

I want to buy two of this

http://www.telepresencegear.com/hdmi-to-usb-3-0-converter/

And use it to capture two cameras - one camcorder , and one microscope camera, to two separate video files. I want them to have the same start time, so it's not like i have two separate capture apps and hit record in both and then have to manually sync them up later. I'm looking for something that can start recording from both of these to separate files that start at the SAME TIME. The camcorder stream will have HDMI audio, the microscope stream will be video only, both will be 1080p60.

Does software in Linux exist that will do this? I asked about using zoneminder for this and offered a donation just to answer the question but never heard back from them. I figure it's an annoying question if no one will answer it even for $100.

Thanks!

[Ant P.]

ffmpeg can do that without a problem using multiple -i and -map options, as long as they both show up as v4l devices.

[thender]

[Ant P.]

You'd be better off reading the wiki as a starting point, the full manual is hard to follow without experience. At the bare minimum here's something that should work (assuming both cameras already configured):

[thender]

[thender]

Since guvcview & cheese work where ffmpeg doesn't, is there a way to get one of those programs to record from two devices with the hit of one button? This would solve everything.

[krinn]

I think AntP gave you the solve.

With many ffmpeg options, they are working only for certain codec, in certain form.
You can map two diff channels of the same file, but i'm not sure AntP trys to map them in two files is what the map option is for. Considering ffmpeg usage of -i what he has suggest would have been more a -o file1 -o file2 in ffmpeg style. But there's just no multi -o usage in ffmpeg.
And again, only in certain format: so be sure to use a container that can handle multi-channels streams.

Record from the two streams in entry so they are sync, and map them within the same file to two channels.
Once done, you have a file with two streams that were record at the same time. You can then easy extract them into two separate files to do what you want with them.

[Ant P.]

Whoops, meant to write -video_size instead of -size. Or just -s works.

I'm not sure why your shell isn't interpreting a backslash line continuation correctly. Try it without.

[thender]

I tried

ffmpeg -framerate 10 -video_size vga -i /dev/video0

then

ffmpeg -f yuv -framerate 10 -video_size vga -i /dev/video0

then

ffmpeg -f v4l2 -framerate 10 -video_size vga -i /dev/video0

then

ffmpeg -f mjpg -framerate 10 -video_size vga -i /dev/video0

then

ffmpeg -f mjpeg -framerate 10 -video_size vga -i /dev/video0

Nothing, just errors on unknown input format

Here is the output of v42l listing the formats I can capture.

[thender]

I figured this was impossible. Ah well.

[Chiitoo]

[thender]

The problem is that it does not understand the v4l2 format at all. See below.

[krinn]

[thender]

[thender]

[krinn]

[thender]

I figured this out last night.. not figured out, but I tried typing the command and it magically worked. I didn't go back to figure out why. I was hoping it would be for something less stupid. God damn am I dumb!

[thender]

I got the USB dongle and it works great. Silly question though. It is supposed to support audio via the HDMI in. I can't find the device in pulse, and if I pull up guvcviewer, I see pulse, and my basic intel hdaudio integrated. Any clue or hint as to how I can look up if this thing really supports audio inan HDMI stream using V4L2?

Hopefully there is a simple solution and I just have shit in my ears this time.

This is the dongle. Pretty amazing for video so far

[thender]

I got the USB dongle and it works great. Silly question though. It is supposed to support audio via the HDMI in. I can't find the device in pulse, and if I pull up guvcviewer, I see pulse, and my basic intel hdaudio integrated. Any clue or hint as to how I can look up if this thing really supports audio in an HDMI stream using V4L2?

I tried this command to see what audio input devices were attached, and it doesn't recognize the dongle as anything.

[thender]

I recompiled my kernel and enabled some more options in the sound section. so now I get this.

[thender]

the cool thing is I found a line that works to record lossless audio & video from it

ffmpeg -f v4l2 -framerate 60 -s 1920x1080 -i /dev/video1 -f alsa -i pulse -c:v libx264 -crf 0 -preset ultrafast -c:a pcm_s16le outfile.mkv

the sad part is it only works 1 in 20 times. The other times, you get this.

[thender]

And solved!

Kernel 3.16.1 is absolutely useless for V4L2. 3.14.14 works amazing. No bugs, no buffer nonsense. If you want to use HDMI to USB3 capture dongles with Linux, avoid kernels in ~amd64.

You still get this silly nonsense with haswell integrated audio where everyone sounds like a chipmunk, but that is easily fixed. https://forums.gentoo.org/viewtopic-p-7568876-highlight-.html#7568876

Not only does the V4L2 driver in 3.14.14 work every time - CPU usage is close to nil! Here is the command line I was using before,and getting 110-130% CPU usage on. It is for realtime, lossless compression of the rawvideo stream.

ffmpeg -f v4l2 -framerate 60 -s 1920x1080 -i /dev/video0 -f alsa -i pulse -c:v libx264 -crf 0 -preset ultrafast -c:a pcm_s16le outfile.mkv

Now I get 33% CPU usage for doing the same thing. I am quite happy!

[thender]

Sometimes I get this in the middle ofa recording, and it dies. I've tried different dongles, same thing.

"Some buffers are still owned by the caller on close."

Is there a way to either

a) Fix this

b) Get it to make a sound when this happens so I know to look up and start the recording again?

[thender]

I solved this issue completely and want to go over everything I did to solve it incase anyone else decides to use their machine for the same purpose.

My goal was to record two lossless and/or uncompressed audio & video streams in realtime, together, in sync for editing later, so I can switch back and forth between them or have a splitscreen view where you can see the two cameras at the same time. I am using two Magewell XI100DUSB-HDMI capture dongles, and a dual core laptop. I spoke to many, many people who work in pro video and I was told what I am looking to achieve would not be possible without $1500-$2000 in capture hardware, $800-$1200 in software, and a top of the line octo-core computer. I am currently achieving this task with a dual core laptop with two cheap SSDs in RAID 0, with free software, with $300 capture dongles, and have no issues at all.

I hope this helps someone else in the same place!!

So that buffers owned by callers on close thing is an ffmpeg isolated issue. I finally solved this to my liking by switching to cvlc. The documentation is 100x more confusing, as is the command line syntax, so I just cobbled together what I could from the manual and from reading example posts from others. It really is a lot more confusing than ffmpeg's documentation.

I used this code to record lossless video & uncompressed audio from the camcorder

[GetOperational]

thender: I find your posts very interesting. I hear you on the advice from "video pros" that have this condescending attitude of "you need to step up to the big leagues and drop $5000 like me, otherwise it's impossible". Technology changes but their advice stays the same long after it has ceased to be accurate.

I have spent a great deal of time figuring out how to do lossless 60fps capture and editing using ffmpeg/x11grab. This works well for screencasts, however one thing I cannot do is capture 60fps lossless video in Linux from an external source.

I check every couple months to see if there is something that meets my needs and have come up empty every time, usually the dealbreakers are:
device only works in windows and requires the use of garbage software from the manufacturer to do anything (I'm looking at you Avermedia)
device can't do 60fps at 1080p
device can do 60fps at 1080p but only at a reduced bitrate
device does its own lossy hardware encoding, or downsamples to yuv420 colorspace, making lossless capture impossible
device is super expensive and can only do lossless capture into manufacturer-specific video formats (Blackmagic)

This Magewell device appears to do everything I need:
1080p60 lossless
no weird drivers or proprietary programs
works in Linux

My remaining reservations are:
There are almost no reviews of this thing, which means it's hard to find unbiased evidence proving it does what it says it does.
Distribution seems very limited, often shipping from China and not available in stores. If it was $20 I wouldn't care but at $300 I want to know it works since returning it would be difficult.
Their specs page says it captures YUY2 and RGB24 colorspace video. I am confused as to why it is able to capture rgb24 in the rgb colorspace but is limited to yuv422 in the yuv colorspace, does this mean it cannot capture yuv444 with ffmpeg?
(update: looks like yuv422 is common amongst almost all capture cards, since it also does rgb24 that's good enough for me.)

Any information from someone with the device would be great.
And thanks again to thender for all the useful info.