Extracting frames from 59.94 FPS video - only every other frame is different

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Extracting frames from 59.94 FPS video - only every other frame is different

Will Price
Hello,

I'm having a strange problem when extracting frames from a video recorded from a GoPro HERO 5 Black camera (1080p, 60FPS, Linear FOV). When I view the extracted frames it appears that every two frames is a duplicate of one another, i.e. frames 1 and 2 look the same, frame 3 shows a change, but frame 4 again looks the same as 3.

I've used `compare` from ImageMagick to actually determine whether the frames are different, and they are, the diff looks like a frame itself but with high brightness. (see frames 1, 2, and the diff at this link: https://drive.google.com/open?id=1Tn3dbZ6Ss7OdhHh6OiJT4qsPXSqCVVgF). If you visually compare frames 1 and 2 then to the human eye they look impercetibly different, yet the diff shows that there is a difference. When I look at the frames in a photo viewer and iterate through them rapidly the apparent motion is much more jerky than in the source video.

If I stitch the frames back together to a video then I get a smooth 60FPS video just like the source.

The motivation for needing smooth non-duplicated frames is because they are to be used as input to an optical flow algorithm which then produces inaccurate optical flow estimations due to the similarity between pairs of frames starting with an odd frame number.

I dumped the frames from the video to a folder using the following command:

$ ffmpeg -i GOPR0325.MP4 'gopro/frame_%06d.jpg'

ffmpeg version 3.4 Copyright (c) 2000-2017 the FFmpeg developers
built with gcc 7.2.0 (GCC)
configuration: --prefix=/usr --disable-debug --disable-static --disable-stripping --enable-avisynth --enable-avresample --enable-fontconfig -
-enable-gmp --enable-gnutls --enable-gpl --enable-ladspa --enable-libass --enable-libbluray --enable-libfreetype --enable-libfribidi --enable-l
ibgsm --enable-libiec61883 --enable-libmodplug --enable-libmp3lame --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopenjpeg -
-enable-libopus --enable-libpulse --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libv4l2 --enable-libvidstab --
enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxcb --enable-libxvid --enable-shared --enable-v
ersion3
libavutil 55. 78.100 / 55. 78.100
libavcodec 57.107.100 / 57.107.100
libavformat 57. 83.100 / 57. 83.100
libavdevice 57. 10.100 / 57. 10.100
libavfilter 6.107.100 / 6.107.100
libavresample 3. 7. 0 / 3. 7. 0
libswscale 4. 8.100 / 4. 8.100
libswresample 2. 9.100 / 2. 9.100
libpostproc 54. 7.100 / 54. 7.100
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x55c3a7e709c0] Using non-standard frame rate 59/1
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'GOPR0325.MP4':
Metadata:
major_brand : mp41
minor_version : 538120216
compatible_brands: mp41
creation_time : 2017-12-01T15:00:48.000000Z
firmware : HD5.02.01.55.00
Duration: 00:00:08.41, start: 0.000000, bitrate: 30249 kb/s
Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuvj420p(pc, bt709), 1920x1080 [SAR 1:1 DAR 16:9], 30110 kb/s, 59.94 fps, 59.94 t
br, 60k tbn, 119.88 tbc (default)
Metadata:
creation_time : 2017-12-01T15:00:48.000000Z
handler_name : GoPro AVC
encoder : GoPro AVC encoder
timecode : 15:16:04:22
Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 128 kb/s (default)
Metadata:
creation_time : 2017-12-01T15:00:48.000000Z
handler_name : GoPro AAC
timecode : 15:16:04:22
Stream #0:2(eng): Data: none (tmcd / 0x64636D74), 0 kb/s (default)
Metadata:
creation_time : 2017-12-01T15:00:48.000000Z
handler_name : GoPro TCD
timecode : 15:16:04:22
Stream #0:3(eng): Data: none (gpmd / 0x646D7067), 29 kb/s (default)
Metadata:
creation_time : 2017-12-01T15:00:48.000000Z
handler_name : GoPro MET
Stream #0:4(eng): Data: none (fdsc / 0x63736466), 14 kb/s (default)
Metadata:
creation_time : 2017-12-01T15:00:48.000000Z
handler_name : GoPro SOS
Stream mapping:
Stream #0:0 -> #0:0 (h264 (native) -> mjpeg (native))
Press [q] to stop, [?] for help
Output #0, image2, to 'gopro/frame_%06d.jpg':
Metadata:
major_brand : mp41
minor_version : 538120216
compatible_brands: mp41
firmware : HD5.02.01.55.00
encoder : Lavf57.83.100
Stream #0:0(eng): Video: mjpeg, yuvj420p(pc), 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 59.94 fps, 59.94 tbn, 59.94 tbc (default)
Metadata:
creation_time : 2017-12-01T15:00:48.000000Z
handler_name : GoPro AVC
timecode : 15:16:04:22
encoder : Lavc57.107.100 mjpeg
Side data:
cpb: bitrate max/min/avg: 0/0/200000 buffer size: 0 vbv_delay: -1
frame= 503 fps= 48 q=24.8 Lsize=N/A time=00:00:08.39 bitrate=N/A speed= 0.8x
video:20242kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown

$ ffprobe GOPR0325.MP4
ffprobe version 3.4 Copyright (c) 2007-2017 the FFmpeg developers
built with gcc 7.2.0 (GCC)
configuration: --prefix=/usr --disable-debug --disable-static --disable-stripping --enable-avisynth --enable-avresample --enable-fontconfig --enable-gmp --enable-gnutls --enable-gpl --enable-ladspa --enable-libass --enable-libbluray --enable-libfreetype --enable-libfribidi --enable-libgsm --enable-libiec61883 --enab
le-libmodplug --enable-libmp3lame --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libv4l2 --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264
--enable-libx265 --enable-libxcb --enable-libxvid --enable-shared --enable-version3
libavutil 55. 78.100 / 55. 78.100
libavcodec 57.107.100 / 57.107.100
libavformat 57. 83.100 / 57. 83.100
libavdevice 57. 10.100 / 57. 10.100
libavfilter 6.107.100 / 6.107.100
libavresample 3. 7. 0 / 3. 7. 0
libswscale 4. 8.100 / 4. 8.100
libswresample 2. 9.100 / 2. 9.100
libpostproc 54. 7.100 / 54. 7.100
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x55ecc7872200] Using non-standard frame rate 59/1
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'GOPR0325.MP4':
Metadata:
major_brand : mp41
minor_version : 538120216
compatible_brands: mp41
creation_time : 2017-12-01T15:00:48.000000Z
firmware : HD5.02.01.55.00
Duration: 00:00:08.41, start: 0.000000, bitrate: 30249 kb/s
Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuvj420p(pc, bt709), 1920x1080 [SAR 1:1 DAR 16:9], 30110 kb/s, 59.94 fps, 59.94 tbr, 60k tbn, 119.88 tbc (default)
Metadata:
creation_time : 2017-12-01T15:00:48.000000Z
handler_name : GoPro AVC
encoder : GoPro AVC encoder
timecode : 15:16:04:22
Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 128 kb/s (default)
Metadata:
creation_time : 2017-12-01T15:00:48.000000Z
handler_name : GoPro AAC
timecode : 15:16:04:22
Stream #0:2(eng): Data: none (tmcd / 0x64636D74), 0 kb/s (default)
Metadata:
creation_time : 2017-12-01T15:00:48.000000Z
handler_name : GoPro TCD
timecode : 15:16:04:22
Stream #0:3(eng): Data: none (gpmd / 0x646D7067), 29 kb/s (default)
Metadata:
creation_time : 2017-12-01T15:00:48.000000Z
handler_name : GoPro MET
Stream #0:4(eng): Data: none (fdsc / 0x63736466), 14 kb/s (default)
Metadata:
creation_time : 2017-12-01T15:00:48.000000Z
handler_name : GoPro SOS
Unsupported codec with id 0 for input stream 2
Unsupported codec with id 0 for input stream 3
Unsupported codec with id 0 for input stream 4

The source video, frames, and diff between frames 1 and 2 are available on google drive: https://drive.google.com/open?id=1Tn3dbZ6Ss7OdhHh6OiJT4qsPXSqCVVgF

Can anyone shed any light on this?

Many thanks,
Will Price
--
Will Price | PhD student | Visual Information Laboratory | University of Bristol
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Re: Extracting frames from 59.94 FPS video - only every other frame is different

Gyan

On 12/1/2017 10:42 PM, Will Price wrote:
> Hello,
>
> I'm having a strange problem when extracting frames from a video recorded from a GoPro HERO 5 Black camera (1080p, 60FPS, Linear FOV). When I view the extracted frames it appears that every two frames is a duplicate of one another, i.e. frames 1 and 2 look the same, frame 3 shows a change, but frame 4 again looks the same as 3.

Mostly a duplicate.

ffprobe GOPR0325.MP4 -show_entries packet=pts_time,size -select_streams
v -read_intervals %+#20 -of compact

shows

packet|pts_time=0.000000|size=365376
packet|pts_time=0.016683|size=5512
packet|pts_time=0.033367|size=72063
packet|pts_time=0.050050|size=15364
packet|pts_time=0.066733|size=63619
packet|pts_time=0.083417|size=17909
packet|pts_time=0.100100|size=75613
packet|pts_time=0.116783|size=17061
packet|pts_time=0.133467|size=72911
packet|pts_time=0.150150|size=21295
packet|pts_time=0.166833|size=77609
packet|pts_time=0.183517|size=20959
packet|pts_time=0.200200|size=86407
packet|pts_time=0.216883|size=16628
packet|pts_time=0.233567|size=87910
packet|pts_time=0.250250|size=22231
packet|pts_time=0.266933|size=92910
packet|pts_time=0.283617|size=11857
packet|pts_time=0.300300|size=90740
packet|pts_time=0.316983|size=24167

Every other frame's size looks to be much smaller. The first frame is an
I-frame and all others are P-frames. When x264 repeats a frame, the size
is usually up to a few hundred bytes.

Is the camera truly registering 60 times a second?

Gyan
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Re: Extracting frames from 59.94 FPS video - only every other frame is different

Rob Hallam-2
In reply to this post by Will Price
On 1 December 2017 at 17:12, Will Price <[hidden email]> wrote:

> I've used `compare` from ImageMagick to actually determine whether the frames are different, and they are, the diff looks like a frame itself but with high brightness. (see frames 1, 2, and the diff at this link: https://drive.google.com/open?id=1Tn3dbZ6Ss7OdhHh6OiJT4qsPXSqCVVgF). If you visually compare frames 1 and 2 then to the human eye they look impercetibly different, yet the diff shows that there is a difference. When I look at the frames in a photo viewer and iterate through them rapidly the apparent motion is much more jerky than in the source video.

I may be barking up the wrong tree, but do you expect to see a
perceptible difference between frames 1 and 2?

I haven't played much with IM's `compare`, but it looks like you are
in an office with possibly fluorescent lights - could the difference
in brightness be different parts of the 50Hz flicker?

> The motivation for needing smooth non-duplicated frames is because they are to be used as input to an optical flow algorithm which then produces inaccurate optical flow estimations due to the similarity between pairs of frames starting with an odd frame number.

Do you need 1920x1080x60 resolution? Would removing the 'similar'
images work? Would increasing the frequency to 120FPS do the trick?Or
higher? Seems like the Hero 5 has access to HEVC
(https://gopro.com/help/articles/block/hevc), is the frame output
issue there as well?

Someone more knowledgeable than I on h264 can perhaps weigh in on how
GoPro record and encode their video. Given the constraints of popular
consumer-level (relatively cheap) hardware aimed at sports / outdoor
activities etc, I wouldn't be surprised if they were doing something
with capture/h264 encoding that gives the behaviour you describe
and/or makes it unsuitable for your purposes.

For confirmation, you could compare the output ffmpeg supplies you
with GoPro's own 'Studio' software:
https://community.gopro.com/t5/GoPro-Apps-for-Desktop/extracting-single-frames-from-videos/td-p/5197

Cheers,
Rob

PS

> ffmpeg version 3.4

You will possibly be told that 'latest git head' is what is officially
supported on the ML!
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Re: Extracting frames from 59.94 FPS video - only every other frame is different

Moritz Barsnick
In reply to this post by Will Price
On Fri, Dec 01, 2017 at 17:12:38 +0000, Will Price wrote:

> If you visually compare frames 1 and 2 then to the human eye they
> look impercetibly different, yet the diff shows that there is a
> difference.

That's certainly due to lossy encoding. Even if the input frames were
identical (assuming for a moment that's what the GoPro is doing),
their actual bitwise content will be different, unless encoding
losslessly.

Moritz
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Re: Extracting frames from 59.94 FPS video - only every other frame is different

Andy Furniss-2
In reply to this post by Will Price
Will Price wrote:
> Hello,
>
> I'm having a strange problem when extracting frames from a video recorded from a GoPro HERO 5 Black camera (1080p, 60FPS, Linear FOV). When I view the extracted frames it appears that every two frames is a duplicate of one another, i.e. frames 1 and 2 look the same, frame 3 shows a change, but frame 4 again looks the same as 3.

Only sometimes - there are also runs of different frames.

> [mov,mp4,m4a,3gp,3g2,mj2 @ 0x55c3a7e709c0] Using non-standard frame rate 59/1

Maybe something to do with this.
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Re: Extracting frames from 59.94 FPS video - only every other frame is different

Andy Furniss-2
Andy Furniss wrote:

> Will Price wrote:
>> Hello,
>>
>> I'm having a strange problem when extracting frames from a video
>> recorded from a GoPro HERO 5 Black camera (1080p, 60FPS, Linear FOV).
>> When I view the extracted frames it appears that every two frames is a
>> duplicate of one another, i.e. frames 1 and 2 look the same, frame 3
>> shows a change, but frame 4 again looks the same as 3.
>
> Only sometimes - there are also runs of different frames.
>
>> [mov,mp4,m4a,3gp,3g2,mj2 @ 0x55c3a7e709c0] Using non-standard frame
>> rate 59/1
>
> Maybe something to do with this.

Though playing the vid that may just be a distraction.

Looks like the early part is duped but the later part mostly isn't.

Maybe it's intended by the camera eg. the early part is lower motion or
lower light level.

Either could be a factor - you could experiment taking other scenes
varying motion or light levels and see if there is a pattern.
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Re: Extracting frames from 59.94 FPS video - only every other frame is different

Moritz Barsnick
On Fri, Dec 01, 2017 at 21:33:32 +0000, Andy Furniss wrote:
> Maybe it's intended by the camera eg. the early part is lower motion or
> lower light level.

Actually, googling for this issue gives a lot of hits, such as this:
https://community.gopro.com/t5/Cameras/High-speed-video-frame-doubling-issues/td-p/15968

So, yes, it's exposure, and you can turn "Auto Exposure" off.

Moritz, no GoPro.
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Re: Extracting frames from 59.94 FPS video - only every other frame is different

Will Price-2
Thank you all for your valuable insights.

It's a real shame that the GoPro does this without warning as it will make our lives more challenging. We need to compute the optical flow of the videos and without an easy method of determining whether frames are 'duplicated' or not we'll have to downsample the videos to 30FPS.

Thanks again,

--
Will Price | PhD student | Visual Information Laboratory | University of Bristol

On Dec 2 2017, at 3:55 am, Moritz Barsnick <[hidden email]> wrote:

> On Fri, Dec 01, 2017 at 21:33:32 +0000, Andy Furniss wrote:
> > Maybe it's intended by the camera eg. the early part is lower motion or
> > lower light level.
>
> Actually, googling for this issue gives a lot of hits, such as this:
> https://community.gopro.com/t5/Cameras/High-speed-video-frame-doubling-issues/td-p/15968
>
> So, yes, it's exposure, and you can turn "Auto Exposure" off.
>
> Moritz, no GoPro.
> _______________________________________________
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> http://ffmpeg.org/mailman/listinfo/ffmpeg-user
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> [hidden email] with subject "unsubscribe".
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Re: Extracting frames from 59.94 FPS video - only every other frame is different

Moritz Barsnick
On Mon, Dec 04, 2017 at 09:46:29 +0000, Will Price wrote:

> It's a real shame that the GoPro does this without warning as it will
> make our lives more challenging. We need to compute the optical flow
> of the videos and without an easy method of determining whether
> frames are 'duplicated' or not we'll have to downsample the videos to
> 30FPS.

Perhaps the optical flow algorithm needs to be improved to cover this.
;-)

No honestly: I personally haven't had the greatest success with the
"decimate" filter, but from its description, it can achieve what you
require: Dropping "nearly identical" frames.

https://ffmpeg.org/ffmpeg-filters.html#decimate-1

The optical flow algorithm then of course needs to understand the
timestamps of the video, as subsequent frames will have varying time
gaps.

Moritz
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Re: Extracting frames from 59.94 FPS video - only every other frame is different

Carl Eugen Hoyos-2
2017-12-04 11:02 GMT+01:00 Moritz Barsnick <[hidden email]>:

> I personally haven't had the greatest success with the
> "decimate" filter, but from its description, it can achieve
> what you require: Dropping "nearly identical" frames.

The releveant filter is called "mpdecimate":
https://ffmpeg.org/ffmpeg-filters.html#mpdecimate

The decimate filter is (part of) an inverse telecine filter
and has a different purpose (the important words in the
description being "at regular intervals" as opposed to
"whenever a frame is duplicated").

Carl Eugen
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Re: Extracting frames from 59.94 FPS video - only every other frame is different

Moritz Barsnick
On Mon, Dec 04, 2017 at 13:28:06 +0100, Carl Eugen Hoyos wrote:

> 2017-12-04 11:02 GMT+01:00 Moritz Barsnick <[hidden email]>:
> > "decimate" filter, but from its description, it can achieve
> > what you require: Dropping "nearly identical" frames.
>
> The releveant filter is called "mpdecimate":
> https://ffmpeg.org/ffmpeg-filters.html#mpdecimate
>
> The decimate filter is (part of) an inverse telecine filter
> and has a different purpose (the important words in the
> description being "at regular intervals" as opposed to
> "whenever a frame is duplicated").

Oh, indeed! Sorry. I should pay more attention to actually reading the
documentation I quote here. D'uh.

Moritz

P.S.: I must try that filter again. Actually, looking at it more
      precisely, I probably tried to use the decimate filter for
      whatever I tried to achieve. Grrr. But its intent isn't totally
      clear (to me) from the docs.
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Re: Extracting frames from 59.94 FPS video - only every other frame is different

Carl Eugen Hoyos-2
2017-12-04 14:25 GMT+01:00 Moritz Barsnick <[hidden email]>:

> P.S.: I must try that filter again. Actually, looking at it more
>       precisely, I probably tried to use the decimate filter for
>       whatever I tried to achieve. Grrr. But its intent isn't totally
>       clear (to me) from the docs.

Which one?

The mpdecimate filter - as you wrote - produces vfr video
which may not always be wanted.

Carl Eugen
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Re: Extracting frames from 59.94 FPS video - only every other frame is different

Moritz Barsnick
On Mon, Dec 04, 2017 at 14:29:25 +0100, Carl Eugen Hoyos wrote:
> 2017-12-04 14:25 GMT+01:00 Moritz Barsnick <[hidden email]>:
> >       clear (to me) from the docs.
>
> Which one?

The decimate filter's practical use isn't clear to me from the docs.

> The mpdecimate filter - as you wrote - produces vfr video
> which may not always be wanted.

I believe that was something I wanted, or could fix with the setpts
filter. I wanted to do stupid minimal motion (change) detection.

OT: Actually, I want a filter which does certain parts of what the
program "motion" does, but not with a camera device, but with an input
video instead. (The advantage of a filter being I could crop the input
first, or omit parts of the timeline, and I could modify it to only
look at certain segements, and so on.) I did have a concept in my head
for what this filter should do, and approx. how, but found to many
filters doing certain elements of this already. I was afraid of
duplicating stuff (though it would have been nice practice), and never
found the spare time.

Moritz
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Re: Extracting frames from 59.94 FPS video - only every other frame is different

Carl Eugen Hoyos-2
2017-12-04 14:41 GMT+01:00 Moritz Barsnick <[hidden email]>:
> On Mon, Dec 04, 2017 at 14:29:25 +0100, Carl Eugen Hoyos wrote:
>> 2017-12-04 14:25 GMT+01:00 Moritz Barsnick <[hidden email]>:
>> >       clear (to me) from the docs.
>>
>> Which one?
>
> The decimate filter's practical use isn't clear to me from the docs.

It is an essential part of one of the inverse telecine filter-chains,
the one that includes the fieldmatch filter (that never drops a
frame and therefore cannot really inverse-telecine by itself).

Carl Eugen
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