display only lines from output that contains a specified word

Question

I'm looking for a way to get only the lines that contains a specified word, in this case all lines that contains the word Stream from an output

I've tried;

streams=$(ffprobe -i  "movie.mp4"  | grep "Stream")

but that didn't get any results..

or do I need to output it to a file and then try to extract the lines I'm looking for?

"grep" should be what you're looking for. Q: What does `ffprobe -i "movie.mp4" | grep "Stream"` look like when you run it from the command line? Perhaps "ffprobe" isn't writing to stdout? Or "Stream" is spelled differently? — paulsm4, Oct 12 '20 at 20:12

score 3 · Accepted Answer · answered Oct 12 '20 at 20:24

3

@paulsm4 was spot on ... the output goes to STDERR.

streams=$(ffprobe -i  "movie.mp4"  |& grep "Stream")

Note the &

answered Oct 12 '20 at 20:24

tink

1

Yes @JoBe ... unix/linux tools typically implement both standard output and standard error as separate streams, in short STDOUT/STDERR ... for some reason the developer of `ffprobe` seems to think of their output as "error" rather than "output", the reason for this I can't quite fathom. – tink Oct 12 '20 at 21:24
The ffmpeg tools have a common logging API. Since ffmpeg can pipe media data over stdout, logs are sent to stderr. – Gyan Oct 15 '20 at 18:59

score 1 · Answer 2 · answered Oct 21 '20 at 20:44

No need for grep. Just use ffprobe directly to get whatever info you need.

Output all info

ffprobe -loglevel error -show_format -show_streams input.mp4

ffprobe -loglevel error -show_streams -select_streams v input.mp4

ffprobe -loglevel error -show_streams -select_streams a input.mp4