FFmpeg simple 1:1 overlay and concatenate? - ffmpeg

Question

I am using ffmpeg on Ubuntu 14.04 (Jon Severinsson's PPA) and am playing video files out of a folder - one by one.
First question I wasn't able to figure out yet - how can I add a simple overlay - 720p footage with 720p overlay (with partial transparency)? So there is no resize or alignment needed - just the 1:1 overlay. I tried a lot already with -vf and -filter_complex but didn't show up.
Second question - with concatenate, is it possible to have the switches between the files seamless? Best without creating a new file - so, on the fly? I need to reduce the gaps between the file switches or eliminate them completely.
This is my bash right now:
#!/usr/bin/env bash
while :; do
files=(*)
ffmpeg -re -i "${files[$RANDOM % ${#files[#]}]}" -acodec copy -vcodec copy -f flv ServerAddress
done
So I have everything in /vod - the videofiles, as well as the overlay.png
Thanks a bunch in advance,
Tim

Answer 1

For the overlay you need to scale the image to the original source dimensions.
To concat multiple source files that have the same codec use the concat demuxer.
Eg:
Make a playlist.txt with the following format:
file '/path/to/file_1'
file '/path/to/file_2'
file '/path/to/file_3'
[..]
And then:
ffmpeg -f concat -i playlist.txt -i overlay.png -filter_complex "[1:v] scale=1280:720 [ovr];[0:v][ovr] overlay=0:0" ...
If the video and the image are the same size you can just use:
ffmpeg -f concat -i playlist.txt -i overlay.png -filter_complex "[0:v] overlay"
Update:
Full example:
You cannot filter and copy the video stream at the same time!
ffmpeg -re -f concat -i playlist.txt -i overlay.png -filter_complex "[0:v] overlay" -c:v h264 -c:a libfdk_aac -ar 44100 -f flv rtmp://...
If your audio stream is valid and has one of the supported audio rates (44100, 22050, 11025) you can do:
ffmpeg -re -f concat -i playlist.txt -i overlay.png -filter_complex "[0:v] overlay" -c:v h264 -c:a copy -f flv rtmp://...