cxadc_vhs_server

A terrible HTTP server made for capturing VHS with two cxadc cards and cxadc-clock-generator-audio-adc or cxadc-clockgen-mod.

Usage

cxadc_vhs_server version|<port>|unix:<socket>

⚠️ Do not expose the server to the public internet. It is not intended to be secure.

Endpoints provided:

• GET /: Hello world.
• GET /version: Version.
• GET /start: Start a capture. Returns a JSON with stats. Parameters:
  • cxadc<number>: Capture /dev/cxadc<number>
  • lname=<device name>: Use <device name> ALSA device for capture. Defaults to hw:CARD=CXADCADCClockGe
  • lformat=<format>: Linear capture format. Defaults to device default.
  • lrate=<rate>: Linear capture sample rate. Defaults to device default.
    • lchannels=<channels>: Linear capture channels. Defaults to device default.
• GET /cxadc: Stream the data being captured from a CX card. Parameters:
  • <number>: Access the <number>th captured card (so if you capture cxadc1 only, you can access it as 0, not 1)
• GET /linear: Stream the data being captured from the ALSA device.
• GET /stats: Capture statistics.
• GET /stop: Stop the current capture. Reports back how many overflows happened.

For more details such as returned JSON format test the endpoints or check the source code.

Examples

Remote capture

Start the server on the capture machine:

$ cxadc_vhs_server 8080

Then queue up the download of the streams:

$ aria2c -Z \
    http://192.168.1.1:8080/linear \
    http://192.168.1.1:8080/cxadc?0 \
    http://192.168.1.1:8080/cxadc?1

Start the capture:

$ curl http://192.168.1.1:8080/start?cxadc0&cxadc1

Once you're done, you just need to stop it:

$ curl http://192.168.1.1:8080/stop

Local capture

The script local-capture.sh is included in the repository to aid with local captures. It runs the sever on a UNIX socket, which is the same thing as used for piping command outputs. The benefit of using the server is the sample drop resilient buffering and better starting point synchronization.

Dependencies

• bash
• curl
• jq
• cxadc_vhs_server
• ffmpeg (optional) with libsoxr (optional)

You can install the first three from most distros' default repositories:

RHEL / Fedora

yum install bash curl jq

Debian / Ubuntu

apt install bash curl jq

The cxadc_vhs_server binary can be obtained from releases, or compiled from sources. The binary releases support glibc 2.17 and later.

A static ffmpeg build with libsoxr can be obtained from https://johnvansickle.com/ffmpeg/. If placed next to the script, it will be used instead of system ffmpeg.

Usage

Usage: local-capture.sh [options] <basepath>
        --video=          Number of CX card to use for video capture (unset=disabled)
        --hifi=           Number of CX card to use for hifi capture (unset=disabled)
        --linear=         ALSA device identifier for linear (unset=default)
        --add-date        Add current date and time to the filenames
        --convert-linear  Convert linear to flac+u8
        --compress-video  Compress video
        --compress-hifi   Compress hifi
        --resample-hifi   Resample hifi to 10 MSps
        --debug           Show commands executed
        --help            Show usage information

Example

$ ./local-capture.sh --video=0 --hifi=1 --convert-linear --compress-video --compress-hifi --resample-hifi test
Server started (PID 3854)
server listening on unix:/tmp/tmp.qDMBd0Ynxu/server.sock
PID 3872 is capturing video to test-video.ldf
PID 3874 is capturing hifi to test-hifi.flac
PID 3876 is capturing linear to test-linear.flac, headswitch to test-headswitch.u8
Capture running... Press 'q' to stop the capture.
Capturing for 0m 0s... Buffers:  0%  0%  0%
Capturing for 0m 5s... Buffers:  0%  0%  0%
q
Stopping capture
Encountered 0 overflows during capture
Waiting for writes to finish...
Killing server
Finished!