[FFmpeg-user] RTSP stream fps 29.97 instead of 30

Post by Jonathan Viney
Hi,
I am pulling an RTSP stream from an Axis 4K IP camera. The stream from the
camera is 30fps, but the resulting stream from ffmpeg is 29.97fps. Here is
ffmpeg -rtsp_transport tcp -i rtsp://10.9.9.1:554/axis-media/media.amp
-loglevel debug
a=framerate:30.000000
The full log output is below. Is there a way to force the framerate to 30
fps?
This video undergoes a second pass where it gets re-encoded, so we could
adjust the frame rate there if necessary. But it would be preferable for it
to be right at this step.
...
v=0
o=- 8374289283112756277 1 IN IP4 10.9.9.1
s=Session streamed with GStreamer
i=rtsp-server
t=0 0
a=tool:GStreamer
a=type:broadcast
a=range:npt=now-
a=control:rtsp://10.9.9.1:554/axis-media/media.amp
m=video 0 RTP/AVP 96
c=IN IP4 0.0.0.0
b=AS:240000
a=rtpmap:96 H264/90000
a=fmtp:96
packetization-mode=1;profile-level-id=640033;sprop-parameter-sets=Z2QAM6w0yAPABD/8BbgICAoAAAfSAAHUwdDAAGP/gAAMf+Nd5caGAAMf/AAAY/8a7y4b04A=,aO48MA==

This SPS in the SDP decodes with:

@126 VUI: timing_info_present_flag 1 ( 1)
@127 VUI: num_units_in_tick 00000000000000000000001111101001 (1001)
@159 VUI: time_scale 00000000000000001110101001100000 (60000)
@191 VUI: fixed_frame_rate_flag 1 ( 1)

That is, the H.264 stream indeed has a fixed framerate of 60000/1001/2 ~ 29.97fps, and that is what ffmpeg is reading - the RTSP layer is likely lying about it. (You may be able to count frames to check that.)

If you want an exactly 30fps output then you should tell the camera to generate a 30fps stream rather than the 30000/1001fps it currently is.

- Mark
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Jonathan Viney

2017-10-03 20:22:56 UTC

Post by Jonathan Viney
Hi,
I am pulling an RTSP stream from an Axis 4K IP camera. The stream from

the

Post by Jonathan Viney
camera is 30fps, but the resulting stream from ffmpeg is 29.97fps. Here

Post by Jonathan Viney
ffmpeg -rtsp_transport tcp -i rtsp://10.9.9.1:554/axis-media/media.amp
-loglevel debug
a=framerate:30.000000
The full log output is below. Is there a way to force the framerate to 30
fps?
This video undergoes a second pass where it gets re-encoded, so we could
adjust the frame rate there if necessary. But it would be preferable for

Post by Jonathan Viney
to be right at this step.
...
v=0
o=- 8374289283112756277 1 IN IP4 10.9.9.1
s=Session streamed with GStreamer
i=rtsp-server
t=0 0
a=tool:GStreamer
a=type:broadcast
a=range:npt=now-
a=control:rtsp://10.9.9.1:554/axis-media/media.amp
m=video 0 RTP/AVP 96
c=IN IP4 0.0.0.0
b=AS:240000
a=rtpmap:96 H264/90000
a=fmtp:96
packetization-mode=1;profile-level-id=640033;sprop-

parameter-sets=Z2QAM6w0yAPABD/8BbgICAoAAAfSAAHUwdDAAGP/
gAAMf+Nd5caGAAMf/AAAY/8a7y4b04A=,aO48MA==
@126 VUI: timing_info_present_flag 1 (
1)
@127 VUI: num_units_in_tick
00000000000000000000001111101001 (1001)
@159 VUI: time_scale
00000000000000001110101001100000 (60000)
@191 VUI: fixed_frame_rate_flag 1 (
1)
That is, the H.264 stream indeed has a fixed framerate of 60000/1001/2 ~
29.97fps, and that is what ffmpeg is reading - the RTSP layer is likely
lying about it. (You may be able to count frames to check that.)
If you want an exactly 30fps output then you should tell the camera to
generate a 30fps stream rather than the 30000/1001fps it currently is.
- Mark

Thanks Mark. That's interesting, I'll see if there is a way to adjust the
stream from the camera.

How did you decode the data from the sprop-parameter-sets value?

Thanks,
-Jonathan.
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Mark Thompson

2017-10-04 21:20:25 UTC

Post by Jonathan Viney
Hi,
I am pulling an RTSP stream from an Axis 4K IP camera. The stream from

the

Post by Jonathan Viney
camera is 30fps, but the resulting stream from ffmpeg is 29.97fps. Here

Thanks Mark. That's interesting, I'll see if there is a way to adjust the
stream from the camera.
How did you decode the data from the sprop-parameter-sets value?

It's just the SPS and PPS base64 coded: decode the base64, add start codes, feed it to any H.264 stream parser.

- Mark
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Carl Eugen Hoyos

2017-10-05 06:48:34 UTC

Post by Jonathan Viney
parameter-sets=Z2QAM6w0yAPABD/8BbgICAoAAAfSAAHUwdDAAGP/
gAAMf+Nd5caGAAMf/AAAY/8a7y4b04A=,aO48MA==
@126 VUI: timing_info_present_flag 1 (
1)
@127 VUI: num_units_in_tick
00000000000000000000001111101001 (1001)
@159 VUI: time_scale
00000000000000001110101001100000 (60000)
@191 VUI: fixed_frame_rate_flag 1 (
1)
That is, the H.264 stream indeed has a fixed framerate of 60000/1001/2 ~
29.97fps, and that is what ffmpeg is reading - the RTSP layer is likely
lying about it. (You may be able to count frames to check that.)
If you want an exactly 30fps output then you should tell the camera to
generate a 30fps stream rather than the 30000/1001fps it currently is.

Thanks Mark. That's interesting, I'll see if there is a way to adjust the
stream from the camera.
How did you decode the data from the sprop-parameter-sets value?

It's just the SPS and PPS base64 coded: decode the base64,
add start codes, feed it to any H.264 stream parser.

My question would have been:
Where can I find any H.264 stream parser?

Thank you, Carl Eugen
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ffmpe

Mark Thompson

2017-10-05 10:28:31 UTC

Post by Carl Eugen Hoyos

Thanks Mark. That's interesting, I'll see if there is a way to adjust the
stream from the camera.
How did you decode the data from the sprop-parameter-sets value?

It's just the SPS and PPS base64 coded: decode the base64,
add start codes, feed it to any H.264 stream parser.

Where can I find any H.264 stream parser?

<http://ffmpeg.org/pipermail/ffmpeg-devel/2017-September/216249.html> - the trace_headers filter will generate traces like this.

Unfortunately that doesn't actually work for the stream fragment here because outer layers in ffmpeg don't like a stream containing no slices - I instead used the JM reference decoder in this case, which is happy to parse an isolated NAL unit.

- Mark
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Carl Eugen Hoyos

2017-10-05 10:31:00 UTC

Post by Mark Thompson
I instead used the JM reference decoder in this case, which
is happy to parse an isolated NAL unit.

Thank you!

Carl Eugen
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Jonathan Viney

2017-10-30 03:56:03 UTC

Post by Carl Eugen Hoyos

Post by Jonathan Viney
parameter-sets=Z2QAM6w0yAPABD/8BbgICAoAAAfSAAHUwdDAAGP/
gAAMf+Nd5caGAAMf/AAAY/8a7y4b04A=,aO48MA==
@126 VUI: timing_info_present_flag 1

(

Post by Jonathan Viney
1)
@127 VUI: num_units_in_tick
00000000000000000000001111101001 (1001)
@159 VUI: time_scale
00000000000000001110101001100000 (60000)
@191 VUI: fixed_frame_rate_flag 1

(

Post by Jonathan Viney
1)
That is, the H.264 stream indeed has a fixed framerate of 60000/1001/2

Post by Jonathan Viney
29.97fps, and that is what ffmpeg is reading - the RTSP layer is likely
lying about it. (You may be able to count frames to check that.)
If you want an exactly 30fps output then you should tell the camera to
generate a 30fps stream rather than the 30000/1001fps it currently is.

Thanks Mark. That's interesting, I'll see if there is a way to adjust

the