C#•3y ago

❔ ffmpeg pipes

Hello, I've been trying to get ffmpeg to work in my c# project for a few hours now.

        private async void ExtractAudio(Stream input, Stream output)
        {
            var process = new Process
            {
                StartInfo =
                {
                    FileName = "ffmpeg",
                    Arguments = "-i pipe:0 -f mp3 -codec:a libmp3lame -",
                    RedirectStandardInput = true,
                    RedirectStandardOutput = true,
                    UseShellExecute = false,
                    CreateNoWindow = false,
                }
            };

            process.Start();

            var stdin = process.StandardInput.BaseStream;
            input.CopyToAsync(stdin);
            process.StandardOutput.BaseStream.CopyToAsync(output);

            process.WaitForExit();
        }

        private async void ExtractAudio(Stream input, Stream output)
        {
            var process = new Process
            {
                StartInfo =
                {
                    FileName = "ffmpeg",
                    Arguments = "-i pipe:0 -f mp3 -codec:a libmp3lame -",
                    RedirectStandardInput = true,
                    RedirectStandardOutput = true,
                    UseShellExecute = false,
                    CreateNoWindow = false,
                }
            };

            process.Start();

            var stdin = process.StandardInput.BaseStream;
            input.CopyToAsync(stdin);
            process.StandardOutput.BaseStream.CopyToAsync(output);

            process.WaitForExit();
        }

I tried multiple different variations but none seem to work. I basically have a file in-memory and want to pass it to ffmpeg to extract the audio and then give it back to me in-memory. Everytime it runs it seemingly just gets stuck up and doesn't continue at all. Why could that be?

が

がんばるかも•5/28/23, 4:26 PM

you do not seem to be ing the async calls

が

がんばるかも•5/28/23, 4:26 PM

the CopyToAsync calls I mean

が

がんばるかも•5/28/23, 4:28 PM

if you need it to run on a different thread then you should run it on a different thread. async/await does not necessarily mean it involves spawning a new thread

が

がんばるかも•5/28/23, 4:29 PM

though wouldn't it be easy if you just saved the data to a file in a temporary location and pass the path to it instead

ががんばるかも you do not seem to be `await` ing the async calls

Sh1beOP•5/28/23, 4:32 PM

yeah, because I read that apparently while im inputting the file through a buffer its outputting stuff already which leads it to somehow fill up the buffer and makes it stuck up like i just have it right now?

Sh1beOP•5/28/23, 4:33 PM

I will create a new thread for both the reading and inputting calls and try it

ががんばるかも though wouldn't it be easy if you just saved the data to a file in a temporary l...

Sh1beOP•5/28/23, 4:34 PM

that would make it easy probably, but it bugs me that I can't get it to work through pipes which would be much more efficient

が

がんばるかも•5/28/23, 4:34 PM

as long as it's good enough

ががんばるかも as long as it's good enough™️

Sh1beOP•5/28/23, 4:42 PM

okay this doesn't work either, guess I will try to save the data to a file and pass the path to it then

が

がんばるかも•5/28/23, 4:43 PM

better ways to do it would be to use probably. But

が

がんばるかも•5/28/23, 4:43 PM

I'm actually curious

Sh1beOP•5/28/23, 4:43 PM

task.run does the same thing afaik

が

がんばるかも•5/28/23, 4:44 PM

how are you getting the console output if you're redirecting the stdout for receiving the file

SSh1be task.run does the same thing afaik

が

がんばるかも•5/28/23, 4:44 PM

yeah but task run is prettier grinowo

ががんばるかも how are you getting the console output if you're redirecting the stdout for rece...

Sh1beOP•5/28/23, 4:45 PM

I genuinely have no idea, I was confused at first as well

Sh1beOP•5/28/23, 4:45 PM

it doesn't make sense at all

Sh1beOP•5/28/23, 4:46 PM

this is kind of pissing me off

が

がんばるかも•5/28/23, 4:46 PM

is the output from the ffmpeg actually going anywhere

が

がんばるかも•5/28/23, 4:48 PM

just genuinely curious. Usually when I used ffmpeg I'd specify some sort of output explicitly

ががんばるかも is the output from the ffmpeg actually going anywhere

Sh1beOP•5/28/23, 4:48 PM

if I remove the standardOutput copying and set the redirectStandardOutput to false, then I get this in my console which looks like the actual data

Sh1beOP•5/28/23, 4:48 PM

so it is being piped out

が

がんばるかも•5/28/23, 4:48 PM

huh. ok

ががんばるかも is the output from the ffmpeg actually going anywhere

Sh1beOP•5/28/23, 4:49 PM

if you look at the arguments, there is a "-" at the end which tells ffmpeg to spit it out instead of making a file

が

がんばるかも•5/28/23, 4:50 PM

oh ok. apparently it is

が

がんばるかも•5/28/23, 4:50 PM

since it is running in a separate thread

が

がんばるかも•5/28/23, 4:51 PM

might as well as get rid of from the copying threads?

が

がんばるかも•5/28/23, 4:51 PM

so it copies synchronously

が

がんばるかも•5/28/23, 4:52 PM

it looks like the stdin copy part works because it works when you disable stdout redirection

ががんばるかも might as well as get rid of `Async` from the copying threads?

Sh1beOP•5/28/23, 4:52 PM

i can try that

ががんばるかも it looks like the stdin copy part works because it works when you disable stdout...

Sh1beOP•5/28/23, 4:52 PM

yeah it works, it only seems to have a problem piping my stuff back in

が

がんばるかも•5/28/23, 4:52 PM

....or that would be my guess

が

がんばるかも•5/28/23, 4:53 PM

~~if it was me I'd just write to a file~~

Sh1beOP•5/28/23, 4:53 PM

.... aand it does the same thing (doesn't work)

が

がんばるかも•5/28/23, 4:53 PM

sad

ががんばるかも ~~if it was me I'd just write to a file~~

Sh1beOP•5/28/23, 4:53 PM

why do they have a piping feature if it doesn't work

Sh1beOP•5/28/23, 4:53 PM

hopefully somebody more experienced comes around and passes on the knowledge

Sh1beOP•5/28/23, 4:54 PM

else I have seriously wasted 4 hours of my life on practically nothing

が

がんばるかも•5/28/23, 4:54 PM

aaaaaactually

が

がんばるかも•5/28/23, 4:55 PM

hm nevermind. gimme a min

ががんばるかも hm nevermind. gimme a min

Sh1beOP•5/28/23, 4:56 PM

sure, if you have some time maybe you could try something, I mean the MVP code is further up

が

がんばるかも•5/28/23, 5:00 PM

what happens if you call a on an empty stream

が

がんばるかも•5/28/23, 5:01 PM

I'm guessing it does nothing

が

がんばるかも•5/28/23, 5:01 PM

so if my theory is correct, returns immediately because it has nothing to read

が

がんばるかも•5/28/23, 5:01 PM

and because nothing is being read from the buffer ffmpeg waits for the buffer to be emptied

が

がんばるかも•5/28/23, 5:02 PM

but there is noone to empty the buffer

が

がんばるかも•5/28/23, 5:02 PM

deadlock?

が

がんばるかも•5/28/23, 5:02 PM

or is it supposed to block until the end of stream is reached

が

がんばるかも•5/28/23, 5:02 PM

probably it is

が

がんばるかも•5/28/23, 5:02 PM

hmmmmmmmmmmmmmm

が

がんばるかも•5/28/23, 5:05 PM

oh also :(