Videocapture skip frames by pletessier · Pull Request #16190 · opencv/opencv

pletessier · 2019-12-18T13:35:59Z

This pullrequest changes

Add the possibility to skip frames in VideoCapture by using the existing OPENCV_FFMPEG_CAPTURE_OPTIONS environment variable and the AVCodecContext::skip_frame method.

AVDiscard options are :
AVDISCARD_NONE : discard nothing
AVDISCARD_DEFAULT : discard useless packets like 0 size packets in avi
AVDISCARD_NONREF : discard all non reference
AVDISCARD_BIDIR : discard all bidirectional frames
AVDISCARD_NONKEY : discard all frames except keyframes
AVDISCARD_ALL : discard all

For example, if you want VideoCapture to capture only keyframes, you can set the env var :
OPENCV_FFMPEG_CAPTURE_OPTIONS=avdiscard;nonkey

asmorkalov · 2019-12-23T08:19:09Z

@pletessier Thanks for the PR. The changes looks good for me. Could you add simple test for the feature? The simplest solution I see is to use some existing video in opencv_extra, restrict FFmpeg provide key frames only with AVDISCARD_NONKEY option and check if cv::VideoCaptrue returns expected amount of frames. Also please, guard the test with FFMPEG specific macro to not break test for other backends.

pletessier · 2020-01-03T12:58:49Z

Hi @asmorkalov,
Thanks for taking this PR.
I wrote a test that works pretty well, but I don't know how to set the OPENCV_FFMPEG_CAPTURE_OPTIONS env var only for this single test.

Setting it in my shell before to run the test is breaking some tests using FFMpeg. That was expected.
Setting it in source code with the setenv method is breaking tests also, but only after my new one.
I tried to unset the var with the same setenv method and a empty value, or using the unsetenv method. It doesn't change anything.

Is there another approach I could try ?

asmorkalov · 2020-01-04T19:01:49Z

OPENCV_FFMPEG_CAPTURE_OPTIONS is read at https://github.com/opencv/opencv/blob/master/modules/videoio/src/cap_ffmpeg_impl.hpp#L911. The option is read every time when VideoCapture object is created and opened, so unset should resolve side effects. Please push your test code to discuss it.

pletessier · 2020-01-06T10:05:42Z

@asmorkalov Starting from a clean env, it works fine now !

pletessier · 2020-01-06T14:30:10Z

@asmorkalov Windows tests are failing. Probably because of #9292 (comment).

I can't test on Windows. I am not even sure that the _WIN32 variable is defined...

asmorkalov

@pletessier I have Windows host in my hands and will check it in mean time. Thanks for the test!

modules/videoio/test/test_ffmpeg.cpp

asmorkalov · 2020-01-20T11:37:34Z

Hello @pletessier , I found out the failure reason. OpenCV links FFMPEG using wrapper code to prevent license conflict. When the library is built on Unix and wrapper code is built together with the library as we do not distribute FFMPEG itself. On Windows the wrapper is built as dedicated library and is loaded on the go, if FFMPEG is present in the distribution. Wrapper is built and updated manually and CI just uses old version of the wrapper lib without your skip option.

asmorkalov · 2020-01-20T11:37:38Z

👍

asmorkalov · 2020-01-20T11:39:18Z

@pletessier Please clean up test code and we can merge the path and update pre-built libs after it.

asmorkalov · 2020-01-20T13:17:45Z

👍

asmorkalov · 2020-01-20T13:19:50Z

@pletessier Could you squash your commits to have clean library commit history.

alalek · 2020-01-20T13:49:17Z

You need to skip Windows tests for now (until FFmpeg wrapper got new update) - we can't merge with red builders.

Add this guard for test code:

#ifndef _WIN32  // details: https://github.com/opencv/opencv/pull/16190
...
#endif

alalek · 2020-01-20T15:12:32Z

modules/videoio/src/cap_ffmpeg_impl.hpp

+            else if (strcmp(avdiscard_entry->value, "nonkey") == 0)
+                enc->skip_frame = AVDISCARD_NONKEY;
+            else if (strcmp(avdiscard_entry->value, "nonref") == 0)
+                enc->skip_frame = AVDISCARD_NONREF;


What FFmpeg / libav versions support that? (at least compilation)

Need to properly guard code through "#if"s.

BTW, access to OPENCV_FFMPEG_CAPTURE_OPTIONS is guarded by

#if LIBAVFORMAT_BUILD >= CALC_FFMPEG_VERSION(52, 111, 0)

@alalek All options (except AVDISCARD_NONINTRA) are in use since ffmpeg 0.7 (libavcodec 52.123.0)

First use of AVDISCARD_NONINTRA is in version 2.3 (libavcodec 55.69.100).

I added some checks on LIBAVCODEC_BUILD version in my last commit, and squashed previous ones.

asmorkalov · 2020-01-23T05:30:23Z

👍

asmorkalov · 2020-01-23T05:31:15Z

@alalek Could you take a look and merge the patch?

alalek · 2020-01-25T20:12:50Z

Rebased on 3.4 branch and "disabled" test:

currently there is no way to detect LIBAV or old FFmpeg versions from the test code (to skip / workaround)
test can be launched locally using "--gtest_also_run_disabled_tests" option.

asmorkalov added category: videoio pr: needs test New functionality requires minimal tests set labels Dec 23, 2019

asmorkalov self-assigned this Dec 23, 2019

asmorkalov added the feature label Dec 23, 2019

asmorkalov reviewed Jan 10, 2020

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modules/videoio/test/test_ffmpeg.cpp Outdated Show resolved Hide resolved

asmorkalov removed the pr: needs test New functionality requires minimal tests set label Jan 20, 2020

alalek reviewed Jan 20, 2020

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pletessier force-pushed the videocapture_skip_frames branch 2 times, most recently from fa3f3ec to 20f5063 Compare January 20, 2020 16:58

asmorkalov self-requested a review January 23, 2020 05:30

asmorkalov approved these changes Jan 23, 2020

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pletessier and others added 2 commits January 24, 2020 22:40

enable skipping frames

c024ae6

update videoio_skip test

c6a7990

alalek merged commit 0853085 into opencv:3.4 Jan 26, 2020

alalek mentioned this pull request Jan 28, 2020

Merge 3.4 #16450

Merged

alalek mentioned this pull request Jun 18, 2020

videoio(test): enable test "videoio_skip.read" #17574

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pletessier commented Dec 18, 2019

This pullrequest changes

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