GOP for dummies
30. 3. 2026GOP = Group of Pictures
Chatgpt constructed bash script could look like
#!/usr/bin/env bash
# GOP
input="$1"
RED="\033[31m"
GREEN="\033[32m"
BLUE="\033[34m"
RESET="\033[0m"
ffprobe -v error \
-select_streams v:0 \
-show_frames \
-show_entries frame=pict_type,pkt_size \
-of csv=p=0 "$1" |
awk -F',' -v R="\033[31m" -v G="\033[32m" -v B="\033[34m" -v X="\033[0m" '
{
type=""
size=""
for (i=1; i<=NF; i++) {
if ($i ~ /^[IPB]$/) type=$i
if ($i ~ /^[0-9]+$/) size=$i
}
if (!type && size) type="I"
if (type && size) {
color = (type=="I") ? R : (type=="P") ? G : B
printf "%6d %s%s%s %8d bytes\n", NR, color, type, X, size
}
}
'
Typical cineform mov, all frames are I frames (ffprobe will not return frame type, so script assumes I type):
gop cineform.mov
1 I 1428668 bytes
2 I 1495596 bytes
3 I 1478536 bytes
4 I 1435628 bytes
5 I 1500988 bytes
6 I 1604252 bytes
7 I 1473584 bytes
8 I 1530488 bytes
9 I 1637484 bytes
10 I 1475332 bytes
11 I 1525756 bytes
12 I 1648728 bytes
13 I 1450760 bytes
14 I 1480096 bytes
15 I 1468560 bytes
16 I 1439028 bytes
17 I 1501236 bytes
18 I 1602928 bytes
19 I 1481236 bytes
20 I 1525344 bytes
21 I 1622172 bytes
22 I 1506064 bytes
23 I 1529228 bytes
24 I 1629456 bytes
25 I 1452368 bytes
26 I 1481740 bytes
27 I 1448896 bytes
28 I 1437796 bytes
29 I 1486024 bytes
30 I 1578068 bytes
Typical ultrafast x.264 (screen recording), doesn’t bother with B frames
gop ultrafastAVC.mp4 | head -n 30
1 I 911822 bytes
2 P 123747 bytes
3 P 394756 bytes
4 P 11416 bytes
5 P 6375 bytes
6 P 6773 bytes
7 P 6389 bytes
8 P 26484 bytes
9 P 6701 bytes
10 P 6503 bytes
11 P 6233 bytes
12 P 6066 bytes
13 P 6486 bytes
14 P 6548 bytes
15 P 6248 bytes
16 P 6245 bytes
17 P 59351 bytes
18 P 7809 bytes
19 P 6411 bytes
20 P 6887 bytes
21 P 6560 bytes
22 P 6165 bytes
23 P 6290 bytes
24 P 6671 bytes
25 P 25275 bytes
26 P 6727 bytes
27 P 6814 bytes
28 P 8137 bytes
29 P 7559 bytes
30 P 7283 bytes
Veryslow x.264 preset
gop veryslowAVC.mp4 | head -n 30
1 I 159087 bytes
2 B 30468 bytes
3 B 49405 bytes
4 B 26404 bytes
5 P 106049 bytes
6 B 28771 bytes
7 B 45149 bytes
8 B 24049 bytes
9 P 100280 bytes
10 B 27993 bytes
11 B 43132 bytes
12 B 24211 bytes
13 P 88936 bytes
14 B 24944 bytes
15 B 41915 bytes
16 B 25152 bytes
17 P 92606 bytes
18 B 32308 bytes
19 B 47765 bytes
20 B 22979 bytes
21 P 80585 bytes
22 B 25030 bytes
23 B 51157 bytes
24 B 27996 bytes
25 P 53829 bytes
26 I 138291 bytes
27 B 7836 bytes
28 B 11356 bytes
29 B 7449 bytes
30 P 27069 bytes
50 mbit XDCAM mpeg2 thing, GOP is 12 frames long, encoding type is CBR
gop xdcam.mxf | head -n 30
1 I 250000 bytes
2 B 250000 bytes
3 B 250000 bytes
4 P 250000 bytes
5 B 250000 bytes
6 B 250000 bytes
7 P 250000 bytes
8 B 250000 bytes
9 B 250000 bytes
10 P 250000 bytes
11 B 250000 bytes
12 B 250000 bytes
13 I 250000 bytes
14 B 250000 bytes
15 B 250000 bytes
16 P 250000 bytes
17 B 250000 bytes
18 B 250000 bytes
19 P 250000 bytes
20 B 250000 bytes
21 B 250000 bytes
22 P 250000 bytes
23 B 250000 bytes
24 B 250000 bytes
25 I 250000 bytes
26 B 250000 bytes
27 B 250000 bytes
28 P 250000 bytes
29 B 250000 bytes
30 B 250000 bytes
Very nice.
