Piping raw []byte video to ffmpeg - Go - go

Question

I have a video directly from the http body in a [] byte format:
//Parsing video
videoData, err := ioutil.ReadAll(r.Body)
if err != nil {
w.WriteHeader(UPLOAD_ERROR)
w.Write([]byte("Error uploading the file"))
return
}
and I need a single frame of the video and convert it to a png. This is how someone would do it with a static and encoded file using ffmpeg:
filename := "test.mp4"
width := 640
height := 360
cmd := exec.Command("ffmpeg", "-i", filename, "-vframes", "1", "-s", fmt.Sprintf("%dx%d", width, height), "-f", "singlejpeg", "-")
var buffer bytes.Buffer
cmd.Stdout = &buffer
if cmd.Run() != nil {
panic("could not generate frame")
}
How can I achieve the same with a raw video?
A user from reddit told me that I might achieve this with https://ffmpeg.org/ffmpeg-protocols.html#pipe but I was unable to find any resources.
Any help is appreciated, thanks.
(EDIT: I tried to pipe the []byte array to ffmpeg now, but ffmpeg does not fill in my buffer:
width := 640
height := 360
log.Print("Size of the video: ", len(videoData))
cmd := exec.Command("ffmpeg", "-i", "pipe:0", "-vframes", "1", "-s", fmt.Sprintf("%dx%d", width, height), "-f", "singlejpeg", "-")
cmd.Stdin = bytes.NewReader(videoData)
var imageBuffer bytes.Buffer
cmd.Stdout = &imageBuffer
err := cmd.Run()
if err != nil {
log.Panic("ERROR")
}
imageBytes := imageBuffer.Bytes()
log.Print("Size of the image: ", len(imageBytes))
But I get following error:
[mov,mp4,m4a,3gp,3g2,mj2 # 0x7ff05d002600]stream 0, offset 0x5ded: partial file
pipe:0: Invalid data found when processing input
Finishing stream 0:0 without any data written to it.
frame= 0 fps=0.0 q=0.0
Lsize= 0kB time=-577014:32:22.77 bitrate= -0.0kbits/s speed=N/A
video:0kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB
muxing overhead: unknown
Output file is empty, nothing was encoded (check -ss / -t / -frames parameters if used)

Answer 1

I need a single frame of the video and convert it to a png. This is
how someone would do it with ffmpeg.
There is a popular go library that is exactly made for what you search for:
https://github.com/bakape/thumbnailer
thumbnailDimensions := thumbnailer.Dims{Width: 320, Height: 130}
thumbnailOptions := thumbnailer.Options{JPEGQuality:100, MaxSourceDims:thumbnailer.Dims{}, ThumbDims:thumbnailDimensions, AcceptedMimeTypes: nil}
sourceData, thumbnail, err := thumbnailer.ProcessBuffer(videoData, thumbnailOptions)
imageBytes := thumbnail.Image.Data
They use ffmpeg under the hood, but removes the abstraction for you.

Answer 2

Please check this out, I wrote this to down sample mp3 files to 128k bitrate and it should work with you. Please change the command which suits you:
package main
import (
"bytes"
"io/ioutil"
"log"
"os"
"os/exec"
)
func check(err error) {
if err != nil {
log.Fatalln(err)
}
}
func main() {
file, err := os.Open("test.mp3") // open file
check(err)
defer file.Close()
buf, err := ioutil.ReadAll(file)
check(err)
cmd := exec.Command("ffmpeg", "-y", // Yes to all
//"-hide_banner", "-loglevel", "panic", // Hide all logs
"-i", "pipe:0", // take stdin as input
"-map_metadata", "-1", // strip out all (mostly) metadata
"-c:a", "libmp3lame", // use mp3 lame codec
"-vsync", "2", // suppress "Frame rate very high for a muxer not efficiently supporting it"
"-b:a", "128k", // Down sample audio birate to 128k
"-f", "mp3", // using mp3 muxer (IMPORTANT, output data to pipe require manual muxer selecting)
"pipe:1", // output to stdout
)
resultBuffer := bytes.NewBuffer(make([]byte, 5*1024*1024)) // pre allocate 5MiB buffer
cmd.Stderr = os.Stderr // bind log stream to stderr
cmd.Stdout = resultBuffer // stdout result will be written here
stdin, err := cmd.StdinPipe() // Open stdin pipe
check(err)
err = cmd.Start() // Start a process on another goroutine
check(err)
_, err = stdin.Write(buf) // pump audio data to stdin pipe
check(err)
err = stdin.Close() // close the stdin, or ffmpeg will wait forever
check(err)
err = cmd.Wait() // wait until ffmpeg finish
check(err)
outputFile, err := os.Create("out.mp3") // create new file
check(err)
defer outputFile.Close()
_, err = outputFile.Write(resultBuffer.Bytes()) // write result buffer to file
check(err)
}
Reference: https://gist.github.com/aperture147/ad0f5b965912537d03b0e851bb95bd38