rffmpeg-go

This is a rewrite of joshuaboniface's rffmpeg in Go! This wouldn't be possible without his work.

What is this?

rffmpeg-go is a remote FFmpeg wrapper used to execute FFmpeg commands on a remote server via SSH. It is most useful in situations involving media servers such as Jellyfin, where one might want to perform transcoding actions with FFmpeg on a remote machine or set of machines which can better handle transcoding, take advantage of hardware acceleration, or distribute transcodes across multiple servers for load balancing.

Quick start

Jellyfin Docker

This is the recommended and easiest method, you can use my prebuilt Jellyfin docker image:

ghcr.io/aleksasiriski/jellyfin-rffmpeg

If you want intro-skipper web you can use my other prebuilt Jellyfin Intro Skipper docker image:

ghcr.io/aleksasiriski/jellyfin-rffmpeg-intro-skipper

You can read more about setting up Jellyfin here.

Binary

Go to releases tab and download the latest binary for your OS
Move the downloaded binary somewhere useful, for instance at /usr/local/bin/rffmpeg
Make soft links to the binary named ffmpeg and ffprobe in the same folder
Copy the example config to /etc/rffmpeg/rffmpeg.yml and change the options to your liking. IMPORTANT: If you want to use ENV VARS to change your config, it's required to uncomment all of the options that are desired to be changed by ENV VARS. ENV VARS take precedence over the config file but are IGNORED if the config file has the options commented
Point your media program to use newly available ffmpeg link for rffmpeg-go, for instance at /usr/lib/rffmpeg-go/ffmpeg

Hosts configuration

For remote hosts to be able to transcode files sent by rffmpeg-go it is required for those hosts to have access to the media files that need transcodes as well as the directory which is used to store transcoded media at the same path as the local host running rffmpeg-go.

For example, if using Jellyfin: remote hosts need access to Jellyfin's media files as well as the temporary transcodes directory, and both the media files must be mounted to exactly the same location as they are on the local host.

Setup

The easiest way to setup remote transcoding hosts is to use this docker image:

ghcr.io/aleksasiriski/rffmpeg-worker

In addition to that, the easiest method to share media and transcoding dir is to setup a NFS share.

Adding

To add a target host, use the command:

rffmpeg add [-w/--weight int] [-n/--name string] <hostname/ip>

This command takes the optional weight flag to adjust the weight of the target host (see below) and name flag to set the server name (defaults to the hostname). A host can be added more than once under a different name.

Removing

To remove a target host, use the command:

rffmpeg remove <name>

This command takes a specific target server name. Removing an in-use target host will not terminate any running processes, though it may result in undefined behaviour within rffmpeg-go. Before removing a host it is best to ensure there is nothing using it.

Logic

Localhost and Fallback

If one of the configured target hosts is called localhost or 127.0.0.1, rffmpeg-go will run the ffmpeg/ffprobe commands locally without SSH. This can be useful if the local machine is also a powerful transcoding device, but you still want to offload some transcoding jobs to other machines.

In addition, rffmpeg-go will fall back to localhost automatically, even if it is not explicitly configured, should it be unable to find any working remote hosts. This helps prevent situations where rffmpeg-go cannot be run due to none of the remote host(s) being available.

In both cases, note that, if hardware acceleration is configured, it must be available on the local host as well, or the ffmpeg commands will fail. There is no easy way around this without rewriting arguments, and this is currently out-of-scope for rffmpeg-go. You should always use a lowest-common-denominator approach when deciding on what additional option(s) to enable, such that any configured host can run any process, or accept that fallback will not work if all remote hosts are unavailable.

The exact path to the local ffmpeg and ffprobe binaries can be overridden in the configuration, should their paths not match those of the remote system(s).

Target Host Selection

When more than one target host is present, rffmpeg-go uses the following rules to select a target host. These rules are evaluated each time a new rffmpeg-go alias process is spawned based on the current state (actively running processes, etc.).

Any hosts marked bad are ignored.
All remaining hosts are iterated through in an indeterminate order. For each host:

a. If the host is not localhost/127.0.0.1, it is tested to ensure it is reachable (responds to ffmpeg -version over SSH). If it is not reachable, it is marked bad for the duration of this processes' runtime and skipped.

b. If the host is idle (has no running processes), it is immediately chosen and the iteration stops.

c. If the host is active (has at least one running process), it is checked against the host with the current fewest number of processes, adjusted for host weight. If it has the fewest, it takes over this role.
Once all hosts have been iterated through, at least one host should have been chosen: either the first idle host, or the host with the fewest number of active processes. rffmpeg-go will then begin running against this host. If no valid target host was found, localhost is used (see section Localhost and Fallback above).

Target Host Weights and Duplicated Target Hosts

When adding a host to rffmpeg-go, a weight can be specified. Weights are used during the calculation of the fewest number of processes among hosts. The actual number of processes running on the host is floor divided (rounded down to the nearest divisible integer) by the weight to give a "weighted count", which is then used in the determination. This option allows one host to take on more processes than other nodes, as it will be chosen as the "least busy" host more often.

For example, consider two hosts: host1 with weight 1, and host2 with weight 5. host2 would have its actual number of processes floor divided by 5, and thus any number of processes under 5 would count as 0, any number of processes between 5 and 10 would count as 1, and so on, resulting in host2 being chosen over host1 even if it had several processes. Thus, host2 would on average handle 5x more ffmpeg processes than host1 would.

Host weighting is a fairly blunt instrument, and only becomes important when many simultaneous ffmpeg processes/transcodes are occurring at once across at least 2 remote hosts, and where the target hosts have significantly different performance profiles. Generally leaving all hosts at weight 1 would be sufficient for most use-cases.

Furthermore, it is possible to add a host of the same name more than once in the rffmpeg add command. This is functionally equivalent to setting the host with a higher weight, but may have some subtle effects on host selection beyond what weight alone can do; this is probably not worthwhile but is left in for the option.

`bad` hosts

As mentioned above under Target Host Selection, a host can be marked bad if it does not respond to an ffmpeg -version command in at least 1 second if it is due to be checked as a target for a new rffmpeg-go alias process. This can happen because a host is offline, unreachable, overloaded, or otherwise unresponsive.

Once a host is marked bad, it will remain so for as long as the rffmpeg-go process that marked it bad is running. This can last anywhere from a few seconds (library scan processes, image extraction) to several tens of minutes (a long video transcode). During this time, any new rffmpeg-go processes that start will see that the host is marked as bad and thus skip it for target selection. Once the marking rffmpeg-go process completes or is terminated, the bad status of that host will be cleared, allowing the next run to try it again. This strikes a balance between always retrying known-unresponsive hosts over and over (and thus delaying process startup), and ensuring that hosts will eventually be retried.

If for some reason all configured hosts are marked bad, fallback will be engaged; see the above section Localhost and Fallback for details on what occurs in this situation. An explicit localhost host entry cannot be marked bad.

FAQ

Can `rffmpeg-go` mangle/alter FFMPEG arguments?

Explicitly no. rffmpeg-go is not designed to interact with the arguments that the media server passes to ffmpeg/ffprobe at all, nor will it. This is an explicit design decision due to the massive complexity of FFMpeg - to do this, I would need to create a mapping of just about every possible FFMpeg argument, what it means, and when to turn it on or off, which is way out of scope.

This has a number of side effects:

rffmpeg-go does not know whether hardware acceleration is turned on or not (see above caveats under Localhost and Fallback).
rffmpeg-go does not know what media is playing or where it's outputting files to, and cannot alter these paths.
rffmpeg-go cannot turn on or off special ffmpeg options depending on the host selected.

Thus it is imperative that you set up your entire system correctly for rffmpeg-go to work.

aleksasiriski/rffmpeg-go