Ffmpeg: writing audio and video to a stream in an mpeg format

I had the commands for exporting a video stream to an mpeg file working correctly with the following code:

ffmpeg -r 24 -pix_fmt rgba -s 1280x720 -f rawvideo -y -i -vf vflip -vcodec mpeg1video -qscale 4 -bufsize 500KB -maxrate 5000KB OUTPUT_FILE

Now, I wanted to add the commands so that audio can be used as well since there's no option for that right now.

I've edited the previous command to the next one:

ffmpeg -r 24 -pix_fmt rgba -s 1280x720 -f rawvideo -y -i -f s16le -ac 1 -ar 44100 -i - -acodec pcm_s16le -ac 1 -b:a 320k -ar 44100 -vf vflip -vcodec mpeg1video -qscale 4 -bufsize 500KB -maxrate 5000KB OUTPUT_FILE

So as you can see I added a new input with the settings for the audio I'm going to be inputting (I'm going to test this with the values of a sine wave).

I'm writing the data to the file like this:

// Write a frame to the ffmpeg stream
fwrite(frame, sizeof(unsigned char*) * frameWidth * frameHeight, 1, ffmpeg); 

// Write multiple sound samples per written frame
for (int t = 0; t < 44100/24; ++t)
    fwrite(&audio, sizeof(short int), 1, ffmpeg);

The first line is the one that only writes the video (where the frame object is a render to texture from the video I'm inputting) After that I'm trying to add the audio. I'm using a for-loop so I can use multiple samples per video frame (because otherwise you would only have 24 audio samples per second)

This does render with a couple of issues:

• 
  

  The rendered video shows green flashes

  
  


• 
  

  The video slides across the screen. For example, if it slides 200 pixels to the right those pixels get rendered at the other side. Also a bit of the frame that should be at the bottom is rendered at the top (so the frame also slides down but this is a constant, it doesn't move over time)

  
  

I can't figure out where my mistake is. I've tried multiple codecs and tried different orders for the commands but it stays the same or gets worse.

Thanks in advance