HANDY TIP: Using FFprobe for stream analysis

HANDY TIP:

You can easily extract bitrate data and frame types (I,P,B) using FFprobe.

At the time of writing, FFprobe version SVN-r92, Copyright (c) 2007-2009 Stefano Sabatini works for frame analysis amongst many other things. The FFprobe attachment to the trunk of FFmpeg version SVN-r23145, Copyright (c) 2000-2010 the FFmpeg developers is not fully complete. Never fear, it works great anyway. Just install the SVN-r92 FFprobe version and run it manually.

./ffprobe -show_frames -pretty two_pass.mp4

...produces this output:

[FRAME]
codec_type=video
pict_type=I
width=1024
height=576
quality=0
coded_picture_number=0
display_picture_number=0
interlaced_frame=0
repeat_pict=0
reference=3
stream_index=0
size=822.000 byte
pkt_pts=0:00:00.000000
pkt_dts=0:00:00.960000
pkt_duration=0:00:00.040000
file_pkt_nb=1
stream_pkt_nb=1
pkt_flag_key=K
[/FRAME]
...etc.

This is repeated for every frame of video which can be a VERY long list. You can filter the list by piping the output to the grep command.

./ffprobe -show_frames -pretty two_pass.mp4 | grep 'size\|pict_type\|coded_picture_number'

pict_type=I
coded_picture_number=0
size=822.000 byte
pict_type=P
coded_picture_number=1
size=219.000 byte
pict_type=P
coded_picture_number=2
size=515.000 byte
pict_type=P
coded_picture_number=3
size=942.000 byte
pict_type=B
coded_picture_number=5
size=2.292 Kibyte
pict_type=P
coded_picture_number=4
size=3.896 Kibyte
pict_type=B
coded_picture_number=7
size=5.546 Kibyte
...etc.

(Note the frame reordering in the structure of the file.)

Now the challenge is to create an open source graphing program for this data.

Any thoughts?




Michael

"half-way to world domination A.K.A. the belligerent blue bike shed"

Thanks Rodney.

I will investigate.

Michael

"half-way to world domination A.K.A. the belligerent blue bike shed"

Hi Michael. The syntax for sed and awk can be tricky, and they can both do pretty advanced stuff. I think awk may be the more appropriate tool for this, although it could be done directly using either Python or Perl too (but I'm not a programmer so I'm not the right person to ask about that).

Mind you, I'm no expert on awk or sed either, but I know that you can use either one to achieve what you want. Sed (Stream EDitor) is designed for line-by-line string editing/replacement, whereas awk is more powerful and probably more suited to parsing the data output from ffprobe and rewriting it into the format that you need for gnuplot. That is my understanding, anyway.

After a bit of tinkering, I think I have got the result I was looking for. Open source bitrate graphing with frame type identification. The following two images are the results of one pass and two pass x264 encoding with FFmpeg. IPB frames are identified by colour. NOTE: As labelled, the y dimension is measured in Bytes per frame.





For context or interest, this is the test video that I have used for this experiment. (I created it with Blender, another great open source program;-)



I chose/created this video specifically for its inherently variable bitrate structure.

For the unix minded, how I did it?

Let me know if you get stuck;-)

# SOFTWARE NEEDED (all open source)
FFmpeg (>SVN-r23145), FFprobe FFprobe (>SVN-r92, currently being merged into FFmpeg as of time of posting) gnuplot (>4.2), grep, sed.

# COMMAND LINE
./ffprobe -show_frames funnyhq.mp4 | grep 'size\|coded_picture_number\|pict_type' > raw.dat && paste -s -d '\t\t\n' raw.dat > fixed.dat && sed -e 's/coded_picture_number=//g' -e 's/size=//g' -e 's/pict_type=//g' -e 's/I/167116800/g' -e 's/P/65280/g' -e 's/B/255/g' fixed.dat > column.dat && gnuplot plot.txt

# GNUPLOT "plot.txt"
set title "1pass"
set xlabel "frame number\n\n./ffmpeg -i funny_bubbles.mov -vcodec libx264 -vpre hq -b 1500k funnyhq.mp4"
set ylabel "Bytes per frame"
set yrange [0:35000]
set ytics (35000, 30000, 25000, 20000, 15000, 10000, 5000)
set xrange [-10:850]
set lmargin 12
set rmargin 2
set grid
set pointsize 2
set label 1 "I frames"
set label 1 at graph .85, .96 tc lt 1
set label 2 "P frames"
set label 2 at graph .85, .92 tc lt 2
set label 3 "B frames"
set label 3 at graph .85, .88 tc lt 3
plot 'column.dat' using 2:3:1 notitle with i lc rgb variable

Now, to work out how to write a sh script to make it easier.

Michael

"half-way to world domination A.K.A. the belligerent blue bike shed"

pretty impressive huh!
Can you point me to a win32 binary of this version of FFprobe.
FFprobe that is packed with the daily builds of FFmpeg does not contain the -show_frames option.

John

Hi,
Is it possible to use the same tool for files with asf formats. Because i tried with asf on Windows. I was able to parse it but I am not getting the size of each frame.

Kindly help