ytcast

cast YouTube videos to your smart TV from command-line.

this program does roughly the same thing as the "Play on TV" button that appears on the player bar when you visit youtube.com with Chrome or when you use the YouTube smartphone app:

(the feature is also described here).

I don't use Chrome as my daily driver because of reasons and I tend to use my smartphone the least as possible when I'm at home... but still I want the "Play on TV" functionality to watch videos on the big television screen without having to search them with the remote! this is why I wrote this tool. also my computing workflow is "command-line centric" and ytcast fits well in my toolbox (see other tools).

ytcast-demo-small.mp4

(video demo on YouTube if above doesn't play).

contents

• usage
• install
• how it works
• BUGS
• workarounds
• THANKS
• other tools

usage

• the computer running ytcast and the target device must be on the same network.
• the target device must support the DIAL protocol (see how it works).
• the target device must have the YouTube on TV app already installed.

run ytcast -h for the full usage, here I'll show the basic options.

the -d (device) option selects the target device matching by name, hostname (ip), or unique service name:

$ ytcast -d fire https://www.youtube.com/watch?v=dQw4w9WgXcQ

to see the already discovered (cached) devices use the -l (list) option:

$ ytcast -l
28bc7426 192.168.1.35    "FireTVStick di Marco"         cached lastused
d0881fbe 192.168.1.227   "[LG] webOS TV UM7100PLB"      cached

to update the devices cache use the -s (search) option (it's implicit when the cache is empty or when -d doesn't match anything in the cache):

$ ytcast -s
28bc7426 192.168.1.35    "FireTVStick di Marco"         lastused
d0881fbe 192.168.1.227   "[LG] webOS TV UM7100PLB"      cached

if your target device doesn't show up, you can try increasing the search timeout with the -t (timeout) option to give the device more time to respond to the query:

$ ytcast -s -t 10s
28bc7426 192.168.1.35    "FireTVStick di Marco"         lastused
d0881fbe 192.168.1.227   "[LG] webOS TV UM7100PLB"      cached

remember that the computer and the target device must be on the same network. if it doesn't show up after several tries, you may consider using the -pair option to skip the discovery process altogether. this adds some limitations though, see workarounds.

to cast to the last used device use the -p option:

$ ytcast -p https://www.youtube.com/watch?v=dQw4w9WgXcQ

when no url is passed in the arguments, ytcast reads video urls (or ids) from stdin one per line:

$ ytcast -d lg < watchlist

this makes it easy to combine ytcast with other tools like ytfzf or my ytfzf clone ytsearch.

to see what's going on under the hood use the -verbose option:

$ ytsearch fireplace 10 hours | ytcast -d lg -verbose
21:13:08 ytcast.go:82: ytcast v0.1.0-6-g8e6daeb
21:13:08 ytcast.go:168: mkdir -p /home/marco/.cache/ytcast
21:13:08 ytcast.go:177: loading cache /home/marco/.cache/ytcast/ytcast.json
21:13:08 ytcast.go:319: reading videos from stdin
21:13:15 dial.go:153: GET http://192.168.1.227:1754/
21:13:15 dial.go:153: GET http://192.168.1.227:36866/apps/YouTube
21:13:15 ytcast.go:293: "YouTube" is stopped on "[LG] webOS TV UM7100PLB"
21:13:15 ytcast.go:306: launching "YouTube" on "[LG] webOS TV UM7100PLB"
21:13:15 dial.go:153: POST http://192.168.1.227:36866/apps/YouTube
21:13:18 dial.go:153: GET http://192.168.1.227:36866/apps/YouTube
21:13:18 ytcast.go:293: "YouTube" is running on "[LG] webOS TV UM7100PLB"
21:13:18 ytcast.go:358: requesting YouTube Lounge to play [cdKop6aixVE] on "[LG] webOS TV UM7100PLB"
21:13:18 remote.go:233: POST https://www.youtube.com/api/lounge/bc/bind
21:13:18 remote.go:233: POST https://www.youtube.com/api/lounge/bc/bind
21:13:18 ytcast.go:197: saving cache /home/marco/.cache/ytcast/ytcast.json

(please run with -verbose and attach the log when reporting an issue).

install

you can get a pre-compiled binary from the latest release assets and copy it somewhere in your $PATH.

here a quick and dirty one-liner script to do it fast on unix-like systems (adjust target and dir to your needs, lookup available targets in the latest release assets):

(target="linux-amd64"; dir="$HOME/bin"; \
  wget -O - https://api.github.com/repos/MarcoLucidi01/ytcast/releases/latest \
    | jq -r --arg target "$target" '.assets[] | select(.name | match("checksums|"+$target)) | .browser_download_url' \
    | wget -i - \
   && sha256sum -c --ignore-missing ytcast-v*-checksums.txt \
   && tar -vxf ytcast-v*"$target.tar.gz" \
   && install -m 755 ytcast-v*"$target/ytcast" "$dir")

if you run Arch Linux (btw I don't) you can get ytcast-bin from the AUR (many thanks to the maintainer)!

if your os or architecture are not available, or you want to get the latest changes from master, you can compile from source. a go compiler and make are required for building and installing:

$ git clone https://github.com/MarcoLucidi01/ytcast.git
...
$ cd ytcast
$ make install
...

make install installs in /usr/local/bin by default, you can change PREFIX if you want, for example I like to keep my binaries inside $HOME/bin so I usually install with:

$ make install PREFIX=$HOME
...
go build -trimpath -tags netgo,osusergo -ldflags="-w -s -X main.progVersion=v0.5.0-3-gd513b8e" -o ytcast
mkdir -p /home/marco/bin
install -m 755 ytcast /home/marco/bin

to uninstall run make uninstall (with the same PREFIX used for install).

how it works

I've always been curious to know how my phone can find my TV on my home network and instruct it to start the YouTube on TV app and play a video right away without basically any manual pairing.

I did some research and found about this nice little protocol called DIAL (DIscovery And Launch) developed by Netflix and Google which does the initial part i.e. allows second-screen devices (phone, laptop, etc..) to discover and launch apps on first-screen devices (TV, set-top, blu-ray, etc..). there is a 40 pages specification and a reference implementation for this protocol.

the discovery part of DIAL is actually performed using another protocol, SSDP (Simple Service Discovery Protocol), which in turn is part of UPnP.

all this is not enough to play videos. once the YouTube on TV app is started by DIAL, we need some other way to "tell" the app which video we want to play (actually DIAL allows to pass parameters to an app you want to launch, but this mechanism is not used by the YouTube on TV app anymore).

after a little more research, I found about the YouTube Lounge api which is used by Chrome and the YouTube smartphone app to remotely control the YouTube on TV app. it allows to start playing videos, pause, unpause, skip, add videos to the queue and more. the api is not documented and understanding how it works it's not an easy and fun job. luckily lots of people have already reverse engineered the thing (see THANKS) so all I had to do was taking the bits I needed to build ytcast.

the bridge between DIAL and YouTube Lounge api is the screenId which as you can imagine is an identifier for your "screen" (TV app). DIAL allows to get information about the current "state" of an app on a particular device. some fields of this state are required by DIAL, other fields are app specific (called additional data). screenId is a YouTube specific field that can be used to get a token from the YouTube Lounge api: with that token we can control the YouTube on TV app via api calls.

putting all together, what ytcast does is:

1. search DIAL enabled devices on the local network (SSDP)
2. get the state of the YouTube on TV app on the target device (DIAL)
3. if the app is stopped, start it (DIAL)
4. get the screenId of the app (DIAL)
5. get a token for that screenId (Lounge)
6. call the api's "play video endpoint" passing the token and the video urls to play (Lounge)

(there is a "devices cache" involved so ytcast won't necessarily do all these steps every time, also if the target device is turned off, ytcast tries to wake it up with Wake-on-Lan).

as you may have already guessed, all this can stop working at any time! the weakest point is the YouTube Lounge api since it's not documented and ytcast depends heavily on it. moreover, ytcast may not work at all on your setup! I use and test ytcast with 2 devices:

• Amazon Fire TV Stick
• LG Smart TV running WebOS

that's all I have. ytcast works great with both these devices but I don't know if it will work well on setups different than mine (it should, but I don't know for sure). if it doesn't work on your setup please open an issue describing your setup and attach a -verbose log so we can investigate what's wrong and hopefully fix it.

also Chromecast. I don't own a Chromecast and you'll probably need to use the -pair option (see workarounds) to make ytcast work with Chromecast because it doesn't use the DIAL protocol anymore, but switched to mDNS for discovery.

BUGS

• sometimes the playing queue gets "messed up" i.e. some videos are added between others, some videos don't get added at all or even an old queue might be "reused" so you could see videos from an old session after the ones you requested to play. unfortunately, using (or misusing) an undocumented api may lead to these kinds of problems and I haven't bothered too much trying to fix them.

• the -a (add) option is slower because it does an api call for each video you want to add and adds a random "sleep delay" before each call. without this delay, the queue gets messed up more easily and videos get lost i.e. they don't get added to the queue.

• playing a video from a specific starting time (t parameter in urls) works only for the first video and only if you are not using the -a (add) option.

• ytcast doesn't appear in Settings > Linked devices menu. it used to show up there and there was a button to "unlink all devices" which caused the screenId to change, but a YouTube update "broke" this feature.

workarounds

• some devices don't support the DIAL protocol (notably Chromecast) so they can't be discovered by ytcast. the YouTube on TV app has a "link with code" functionality which can be used as workaround to pair ytcast with these devices. the pairing code can be found in Settings > Link with TV code and then you can use the -pair option to do the pairing:

  $ ytcast -pair 123456789101
  8a59f138 unknown         "YouTube on TV"
  

  once paired you can cast videos in the usual way:

  $ ytcast -d 8a59 https://www.youtube.com/watch?v=t0Q2otsqC4I
  

  when using this method, ytcast and the target device do not need to be on the same network, but it adds many manual steps i.e. the YouTube on TV app must be already open because ytcast won't be able to start it nor to Wake-On-Lan the TV and it won't automatically "re-pair" when the screenId changes (I don't know how often that happens).

• playlist urls don't work with ytcast, I haven't found a reliable way to pass playlist ids to the api. youtube-dl comes to the rescue (see also other tools) since it can extract all video urls of YouTube playlists:

  $ youtube-dl -j --flat-playlist https://www.youtube.com/playlist?list=PLrOv9FMX8xJHqMvSGB_9G9nZZ_4IgteYf | jq -r '.url' | ytcast -p
  

  you can of course filter the pipeline as you like and this makes it so flexible that I actually don't feel the need for ytcast to support playlist urls: less is more!

• this might sound obvious, but if you are tired of typing the device name (even a substring of it) every time you want to cast something or if you have multiple devices with the same name, you can define shell aliases and benefit from shell tab-completion feature:

  $ alias ytcbed="ytcast -d 'LG 32'"
  $ ytcbed https://www.youtube.com/watch?v=dQw4w9WgXcQ
  

  (see your shell documentation to make aliases persistent, usually you have to add them in the shell's rc file).

THANKS

I would like to thank all the people whose work has helped me tremendously in building ytcast, especially the following projects/posts:

• https://0x41.cf/automation/2021/03/02/google-assistant-youtube-smart-tvs.html
• https://github.com/thedroidgeek/youtube-cast-automation-api
• https://github.com/mutantmonkey/youtube-remote
• https://bugs.xdavidhu.me/google/2021/04/05/i-built-a-tv-that-plays-all-of-your-private-youtube-videos
• https://github.com/aykevl/plaincast
• https://github.com/ur1katz/casttube

other tools

as I said earlier, my computing environment is very command-line centric and I'd like to showcase the other tools I use to enjoy a "no frills" YouTube experience from the terminal!

• youtube-dl (actually yt-dlp these days) doesn't need introduction, it's an awesome tool and it's well integrated with mpv so I can watch videos with my favorite player without having my laptop fan spin like an airplane engine thanks to this mpv config:

  ytdl-format=bestvideo[height<=?1080][vcodec!=?vp9]+bestaudio/best
  

• ytsearch is my clone of the initial version of ytfzf. it allows to search and select video urls from the command-line using the wonderful fzf (fun fact: it's implemented basically as a single big pipe ahah). you have already seen it in action in ytcast examples, but it works great with mpv too:

  $ ytsearch matrix 4 | xargs mpv
  $ ytsearch 9 symphony | xargs mpv --no-video
  

• ytxrss allows to extract the rss feed url of a YouTube channel starting from a video or channel url. I use rss feeds (newsboat) to keep up-to-date with things and I'm really glad YouTube still supports them for channel uploads. if I'm interested in a channel's future uploads, what I usually do is:

  $ ytxrss https://www.youtube.com/user/Computerphile >> ~/.newsboat/urls
  

---

see license file for copyright and license details.