Interesting symmetry when plotting PTS intervals against frame number on graph… Can anyone explain it?
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So recently I wanted to study whether a transport streams successive PTS timestamps were at regular intervals.
Here's what I did. I used the ffprobe command:
ffprobe -show_frames [input] | grep pkt_pts_time > times.txt
Then I just put those values into excel, and worked out the intervals. And finally plotted it on a graph, with PTS interval on the y-axis, and the PTS timestamp number on the x-axis.
And I see a really cool mirror effect happening about the x-axis. Does anyone have any idea why this is?
mpeg2-ts
asked Nov 22 at 15:02
Baba.S
509
add a comment |
up vote
-1
down vote
favorite
So recently I wanted to study whether a transport streams successive PTS timestamps were at regular intervals.
Here's what I did. I used the ffprobe command:
ffprobe -show_frames [input] | grep pkt_pts_time > times.txt
Then I just put those values into excel, and worked out the intervals. And finally plotted it on a graph, with PTS interval on the y-axis, and the PTS timestamp number on the x-axis.
And I see a really cool mirror effect happening about the x-axis. Does anyone have any idea why this is?
mpeg2-ts
asked Nov 22 at 15:02
Baba.S
509
B frames. Use DTS instead, or sort the pts comumn before calculating frame duration.
– szatmary
Nov 22 at 16:35
@szatmary Just wanted to clear up any confusion on my side. I am assuming the following: 1)The command I use in ffprobe will give by each frame in Presentation order 2) Since the frames are shown in presentation order, the PTS timestamps should therefore be chronological. So this is why its confusing that a particular PTS value can be less than that of a preceding frame's PTS value.
– Baba.S
Nov 22 at 19:29
Your assumptions are wrong. Decode order is not guaranteed to be the same as display order. Google “b frame” all the information is available on the internet.
– szatmary
Nov 22 at 20:58
I understand what a B frame is. It is bi-directional and the decoder needs the I and P frames before it can deal with the B frame. I understand that the access units arrive to the decoder in decode order, and then is re-ordered into presentation order. But I have been told that running the command I used in ffprobe gives the information in PRESENTATION order. Therefore, I find it strange that PTS deltas can be negative... I hope I have made it more clear.
– Baba.S
Nov 23 at 9:26
add a comment |
up vote
-1
down vote
favorite
up vote
-1
down vote
favorite
So recently I wanted to study whether a transport streams successive PTS timestamps were at regular intervals.
Here's what I did. I used the ffprobe command:
ffprobe -show_frames [input] | grep pkt_pts_time > times.txt
Then I just put those values into excel, and worked out the intervals. And finally plotted it on a graph, with PTS interval on the y-axis, and the PTS timestamp number on the x-axis.
And I see a really cool mirror effect happening about the x-axis. Does anyone have any idea why this is?
mpeg2-ts
asked Nov 22 at 15:02
Baba.S
509
So recently I wanted to study whether a transport streams successive PTS timestamps were at regular intervals.
Here's what I did. I used the ffprobe command:
ffprobe -show_frames [input] | grep pkt_pts_time > times.txt
Then I just put those values into excel, and worked out the intervals. And finally plotted it on a graph, with PTS interval on the y-axis, and the PTS timestamp number on the x-axis.
And I see a really cool mirror effect happening about the x-axis. Does anyone have any idea why this is?
mpeg2-ts
mpeg2-ts
asked Nov 22 at 15:02
Baba.S
509
asked Nov 22 at 15:02
Baba.S
509
asked Nov 22 at 15:02
Baba.S
509
asked Nov 22 at 15:02
Baba.S
509
asked Nov 22 at 15:02
Baba.S
509
509
B frames. Use DTS instead, or sort the pts comumn before calculating frame duration.
– szatmary
Nov 22 at 16:35
@szatmary Just wanted to clear up any confusion on my side. I am assuming the following: 1)The command I use in ffprobe will give by each frame in Presentation order 2) Since the frames are shown in presentation order, the PTS timestamps should therefore be chronological. So this is why its confusing that a particular PTS value can be less than that of a preceding frame's PTS value.
– Baba.S
Nov 22 at 19:29
Your assumptions are wrong. Decode order is not guaranteed to be the same as display order. Google “b frame” all the information is available on the internet.
– szatmary
Nov 22 at 20:58
I understand what a B frame is. It is bi-directional and the decoder needs the I and P frames before it can deal with the B frame. I understand that the access units arrive to the decoder in decode order, and then is re-ordered into presentation order. But I have been told that running the command I used in ffprobe gives the information in PRESENTATION order. Therefore, I find it strange that PTS deltas can be negative... I hope I have made it more clear.
– Baba.S
Nov 23 at 9:26
add a comment |
B frames. Use DTS instead, or sort the pts comumn before calculating frame duration.
– szatmary
Nov 22 at 16:35
@szatmary Just wanted to clear up any confusion on my side. I am assuming the following: 1)The command I use in ffprobe will give by each frame in Presentation order 2) Since the frames are shown in presentation order, the PTS timestamps should therefore be chronological. So this is why its confusing that a particular PTS value can be less than that of a preceding frame's PTS value.
– Baba.S
Nov 22 at 19:29
Your assumptions are wrong. Decode order is not guaranteed to be the same as display order. Google “b frame” all the information is available on the internet.
– szatmary
Nov 22 at 20:58
I understand what a B frame is. It is bi-directional and the decoder needs the I and P frames before it can deal with the B frame. I understand that the access units arrive to the decoder in decode order, and then is re-ordered into presentation order. But I have been told that running the command I used in ffprobe gives the information in PRESENTATION order. Therefore, I find it strange that PTS deltas can be negative... I hope I have made it more clear.
– Baba.S
Nov 23 at 9:26
B frames. Use DTS instead, or sort the pts comumn before calculating frame duration.
– szatmary
Nov 22 at 16:35
B frames. Use DTS instead, or sort the pts comumn before calculating frame duration.
– szatmary
Nov 22 at 16:35
@szatmary Just wanted to clear up any confusion on my side. I am assuming the following: 1)The command I use in ffprobe will give by each frame in Presentation order 2) Since the frames are shown in presentation order, the PTS timestamps should therefore be chronological. So this is why its confusing that a particular PTS value can be less than that of a preceding frame's PTS value.
– Baba.S
Nov 22 at 19:29
@szatmary Just wanted to clear up any confusion on my side. I am assuming the following: 1)The command I use in ffprobe will give by each frame in Presentation order 2) Since the frames are shown in presentation order, the PTS timestamps should therefore be chronological. So this is why its confusing that a particular PTS value can be less than that of a preceding frame's PTS value.
– Baba.S
Nov 22 at 19:29
Your assumptions are wrong. Decode order is not guaranteed to be the same as display order. Google “b frame” all the information is available on the internet.
– szatmary
Nov 22 at 20:58
Your assumptions are wrong. Decode order is not guaranteed to be the same as display order. Google “b frame” all the information is available on the internet.
– szatmary
Nov 22 at 20:58
I understand what a B frame is. It is bi-directional and the decoder needs the I and P frames before it can deal with the B frame. I understand that the access units arrive to the decoder in decode order, and then is re-ordered into presentation order. But I have been told that running the command I used in ffprobe gives the information in PRESENTATION order. Therefore, I find it strange that PTS deltas can be negative... I hope I have made it more clear.
– Baba.S
Nov 23 at 9:26
I understand what a B frame is. It is bi-directional and the decoder needs the I and P frames before it can deal with the B frame. I understand that the access units arrive to the decoder in decode order, and then is re-ordered into presentation order. But I have been told that running the command I used in ffprobe gives the information in PRESENTATION order. Therefore, I find it strange that PTS deltas can be negative... I hope I have made it more clear.
– Baba.S
Nov 23 at 9:26
add a comment |
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B frames. Use DTS instead, or sort the pts comumn before calculating frame duration.
– szatmary
Nov 22 at 16:35
@szatmary Just wanted to clear up any confusion on my side. I am assuming the following: 1)The command I use in ffprobe will give by each frame in Presentation order 2) Since the frames are shown in presentation order, the PTS timestamps should therefore be chronological. So this is why its confusing that a particular PTS value can be less than that of a preceding frame's PTS value.
– Baba.S
Nov 22 at 19:29
Your assumptions are wrong. Decode order is not guaranteed to be the same as display order. Google “b frame” all the information is available on the internet.
– szatmary
Nov 22 at 20:58
I understand what a B frame is. It is bi-directional and the decoder needs the I and P frames before it can deal with the B frame. I understand that the access units arrive to the decoder in decode order, and then is re-ordered into presentation order. But I have been told that running the command I used in ffprobe gives the information in PRESENTATION order. Therefore, I find it strange that PTS deltas can be negative... I hope I have made it more clear.
– Baba.S
Nov 23 at 9:26