How to map ffmpeg multiple outputs to pipes

Question

I'm working on a transcoder backend to a project that intends to serve static mpeg-dash manifests and files for a frontend player. And I'm trying to figure out how I can get multiple outputs into multiple pipes from ffmpeg.

One of the backend routes takes in a video file and uses ffmpeg to convert that video file into multiple mpeg-dash representations. I've already got a command working to convert a given mp4 into a manifest, 2 video representations, and 1 audio representation, using the sample command from ffmpeg's wiki:

 ffmpeg -re -i input.mp4 -c:a aac -c:v libx264 -map 0 -map 0 -b:v:0 800k -b:v:1 300k -s:v:1 320x170 -bf 1 -keyint_min 120 -g 120 -sc_threshold 0 -b_strategy 0 -ar:a:1 22050 -use_timeline 1 -use_template 1  -adaptation_sets "id=0,streams=v id=1,streams=a" -single_file 1 -f dash output.mpd

The problem I face is: How do I get the output of this ffmpeg command into pipes instead of files?

Answer 1

For anyone in a similar situation to me of wanting to make a server that transcodes videos uploaded to it, I found a pretty good solution, but it doesn't involve pipes like I originally thought would be best.

As it turns out ffmpeg automatically handles filenames being http urls, so by making a few internal routes for reading/writing objects from a minio bucket, I was able to get this to work.

My final command ended up being something like:

ffmpeg -re -i http://localhost:8080/read/input.mp4 \
  -c:a aac \
  -c:v libx264 \
  -map 0 -map 0 \
  -b:v:0 800k \
  -b:v:1 300k \
  -s:v:1 320x170 \
  -bf 1 \
  -keyint_min 120 \
  -g 120 \
  -sc_threshold 0 \
  -b_strategy 0 \
  -ar:a:1 22050 \
  -use_timeline 1 \
  -use_template 1  \
  -adaptation_sets "id=0,streams=v id=1,streams=a" \
  -single_file 1 \
  -f dash http://localhost:8080/write/output.mpd

This causes all the output streams to make requests to urls like: http://localhost:8080/write/output-stream1.mp4 etc.

An important note is that your read route must support byte ranges for file types (like mp4) that need to be seekable.