Make cv::VideoCapture::get return cv::CAP_PROP_UNKNOWN (-1) for unsupported properties #21337
The return value indicating an unsupported property is not consistent across backends.
I stumbled on this issue because my code was determining if a property value is valid if it's non-zero (like the documentation says), which worked fine on macOS, but not on Android.
For example, auto-exposure is not supported on macOS, so get() returns 0. But it is supported on Android and 0 means auto-exposure is off.
I think -1 is the better return value to indicate unsupported properties.
I made changes to all the backends. I think I got every case. This breaks API compatibility for some backends, so I based this on branch 3.4.
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Fixed write return status in videoio module#29087
closes: https://github.com/opencv/opencv/issues/24287
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videoio(mjpeg): fix heap-buffer-overflow in put_bits off-by-one resize guard #29113
### Summary
Fix a heap-buffer-overflow (WRITE of size 4) in the built-in MJPEG encoder detected by AddressSanitizer during fuzzing.
Fixes#29112
### Root Cause
`mjpeg_buffer::put_bits` in `modules/videoio/src/cap_mjpeg_encoder.cpp` guards buffer resize with:
```cpp
if ((m_pos == (data.size() - 1) && len > bits_free) || m_pos == data.size())
resize(int(2 * data.size()));
```
When `len == bits_free` the guard is **false** (strict `>`), so no resize happens. The subsequent code then:
1. Subtracts `len` from `bits_free`, making it exactly 0.
2. Enters the `bits_free <= 0` branch and executes `++m_pos`.
3. Writes `data[m_pos]` — now equal to `data[data.size()]` — **out of bounds**.
### Fix
Change `len > bits_free` to `len >= bits_free` so the buffer is grown whenever the current slot will be exactly or more than consumed.
```diff
-if ((m_pos == (data.size() - 1) && len > bits_free) || m_pos == data.size())
+if ((m_pos == (data.size() - 1) && len >= bits_free) || m_pos == data.size())
```
### Verification
Reproducer (1×1 grayscale frame, `CAP_OPENCV_MJPEG`):
```cpp
uint8_t pixel = 0xff;
cv::Mat frame(1, 1, CV_8UC1, &pixel);
int fourcc = cv::VideoWriter::fourcc('M', 'J', 'P', 'G');
cv::VideoWriter writer;
writer.open("/tmp/poc.avi", cv::CAP_OPENCV_MJPEG, fourcc, 25.0, cv::Size(1,1), false);
writer.write(frame);
```
Ran under `-fsanitize=address,undefined`; exits cleanly with no error after this fix.
### Regression Test
`TEST(Videoio_MJPEG, put_bits_no_heap_overflow)` added to `modules/videoio/test/test_video_io.cpp` — opens a `CAP_OPENCV_MJPEG` VideoWriter for a 1×1 grayscale file and writes one frame; asserts `EXPECT_NO_THROW`.
Add CAP_PROP_IMAGE_SEQ_START #28844
Resolves https://github.com/opencv/opencv/issues/28843
New CAP_PROP_IMAGE_SEQ_START as an open only property for setting the first frame index when a VideoCap is opening with pattern, squashes test_images TODO.
`CAP_FFMPEG`: forwarded to the image2 demuxers "start_number" option.
`CAP_IMAGES`: Now a WithParams variant so the value reaches open() before probe runs, replaces 0 or 1 auto probe for sequence start.
Property is opt in so default behavior is not affected.
Please note that G_STREAMER is not considered here as I think its out of scope, it already has a "start-index" property and its backend is driven by the pipeline strings rather then these printf patterns.
If an alternative solution is preferred that will not involve a new property or promoting CAP_IMAGES to a "WithParams" variant I don't mind implementing.
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Avfoundation fractional fps seek fix#28833
Accompanied by PR on [opencv_extra](https://github.com/opencv/opencv_extra/pull/1345)
Fixes https://github.com/opencv/opencv/issues/28831
AVFoundation backend seeking slowly drifts for any video which has a non-integer frame rate.
Narrowing of a float `mAssetTrack.nominalFrameRate` to int32_t means fractional rates are treated as integer when seeking by frame number.
Solution implemented in this branch is to use the tracks native rational frame duration when seeking (and available).
I've also included an AVF only test case which uses a new test file in opencv_extra. This test just compares the video caps expected ms vs actual for a known rate file (23.976).
Could consider extending this test to more then just AVF, as from what I can see there are no fractional rate tests / files.
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Fix frame seeking with negative DTS values in FFMPEG backend #27878
**Merge with extra**: https://github.com/opencv/opencv_extra/pull/1289
Fixes https://github.com/opencv/opencv/issues/27819
Fixes https://github.com/opencv/opencv/issues/23472
Accompanied by PR on https://github.com/opencv/opencv_extra/pull/1289
The FFmpeg backend fails to correctly seek in H.264 videos that contain negative DTS values in their initial frames. This is a valid encoding practice used by modern video encoders (such as DaVinci Resolve's current export) where B-frame reordering causes the first few frames to have negative DTS values.
When picture_pts is unavailable (AV_NOPTS_VALUE), the code falls back to using pkt_dts:
`picture_pts = packet_raw.pts != AV_NOPTS_VALUE_ ? packet_raw.pts : packet_raw.dts;`
If this DTS value is negative (which is legal per H.264 spec), it propagates through the frame number calculation:
`frame_number = dts_to_frame_number(picture_pts) - first_frame_number;`
This results in negative frame numbers, messing up seeking operations.
Solution implemented in this branch is a timestamp normalization similar to FFmpegs -avoid_negative_ts_make_zero flag:
- Calculate a global offset once on the first decoded frame by getting the minimum timestamp in either:
- Container start_time
- Stream start_time
- First observed timestamp (PTS, then DTS).
- Apply the offset consistently to all timestamps, shifting negative values to begin at 0 while keeping relative timing.
- Simplify timestamp converters to remove `start_time` subtractions since timestamps are pre-normalized.
This also includes a new test `videoio_ffmpeg.seek_with_negative_dts`
This test verifies that seeking behavior performs as expected on a file which has negative DTS values in the first frames.
A PR on opencv_extra accompanies this one with that testing file: https://github.com/opencv/opencv_extra/pull/1279
```
opencv_extra=ffmpeg-videoio-negative-dts-test-data
```
<cut/>
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Open camera device by index through FFmpeg #27841
### Pull Request Readiness Checklist
resolves https://github.com/opencv/opencv/issues/26812
Example of explicit backend option (similar to `-f v4l2` from command line)
```
export OPENCV_FFMPEG_CAPTURE_OPTIONS="f;v4l2"
```
see https://trac.ffmpeg.org/wiki/Capture/Webcam for available options
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Add Raspberry Pi 4 and 5 V4L2 Stateless HEVC Hardware Acceleration with FFmpeg #27453
This PR enables V4L2 stateless HEVC hardware acceleration for Raspberry Pi 5 within OpenCV's videoio module. It leverages FFmpeg's drm acceleration ([FFmpeg API changes](https://github.com/FFmpeg/FFmpeg/blob/ee1f79b0fa4c82da9c19328b049b593c71611402/doc/APIchanges#L1529)), significantly improving HEVC decoding performance on RPi5 for robotics and embedded vision applications.
I have a working proof-of-concept with local benchmarks showing clear gains.
Checklist Status:
Ready: License, branch (4.x), FFmpeg reference, and (linked) related issue (#27452).
Seeking Guidance: Need help with formal C++ performance/accuracy tests, opencv_extra integration, and full documentation/examples.
As a Python developer, I welcome C++ best practice feedback and assistance with testing setup.
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FIX: CvCapture_FFMPEG::setProperty(CAP_PROP_POS_*) followed by getProperty #27523
Partially fixes#23088 and #23472. This PR fixes `get(CAP_PROP_POS_MSEC)` calls after a `set(CAP_PROP_POS_*)` without calling `read` first.
Since `seek` calls `grabFrame` which already sets `picture_pts`, manually setting `picture_pts` anywhere else in the call stack should not be necessary (except for the special case of seeking to frame 0).
Minimal example from #23088
```cpp
for(int i = 0; i < 3; i++) cap.read(img);
printf("at: %f frames, %f msec\n", cap.get(CAP_PROP_POS_FRAMES), cap.get(CAP_PROP_POS_MSEC));
cap.set(CAP_PROP_POS_FRAMES, 3);
printf("at: %f frames, %f msec\n", cap.get(CAP_PROP_POS_FRAMES), cap.get(CAP_PROP_POS_MSEC));
```
Current
```txt
at: 3.000000 frames, 80.000000 msec
at: 3.000000 frames, 0.234375 msec
```
PR
```txt
at: 3.000000 frames, 80.000000 msec
at: 3.000000 frames, 80.000000 msec
```
It similarly helps with `CAP_PROP_POS_MSEC`:
Current
```txt
at: 3.000000 frames, 80.000000 msec
at: 2.000000 frames, 6.250000 msec
```
PR
```txt
at: 3.000000 frames, 80.000000 msec
at: 2.000000 frames, 40.000000 msec
```
Note the seek operation is still inconsistent between the `CAP_PROP_POS_*` options as mentioned by #23088, and VFR video seeking has issues discussed in #9053. For fixed-frame rate video, we could change 0.5 to 1 in `void CvCapture_FFMPEG::seek(double sec);` to align `CAP_PROP_POS_MSEC` with `CAP_PROP_POS_FRAMES`, but `CAP_POS_AVI_RATIO` and VFR video would still be broken.
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fix#26276: cv::VideoWriter fails writing colorless images #27153
When writing grayscale images (`isColor=false`), `cv::VideoWriter` failed as FFmpeg backend requires input frames to be in a grayscale format. Unlike other backends, FFmpeg doesn't perform this conversion internally and expects the input to be pre-converted. To fix this, I inserted a check in the `CvVideoWriter_FFMPEG_proxy::write` to convert input frames to grayscale when the input has more than 1 channel. If this is true, then the input is converted to a gray image using `cv::cvtColor` (with `cv::COLOR_BGR2GRAY`).
Additionally, as suggested in the issue comments, I have correctly propagated the return value of `CvVideoWriter_FFMPEG::writeFrame` back to the `CvVideoWriter_FFMPEG_proxy::write`. This return value wasn't being used, and `writeFrame` was always returning false since the FFmeg's return code `AVERROR(EAGAIN)` was mistakenly being treated as an error. Now it's handled as a signal for additional input (current input was successfully written, and a new frame should be sent. [See FFmpeg documentation for `avcodec_receive_packet`](https://ffmpeg.org/doxygen/6.1/group__lavc__decoding.html)). A warning is displayed if `CvVideoWriter_FFMPEG::writeFrame` returns false. Alternatively, this could be propagated back up to the user, making cv::VideoWriter::write a boolean.
Finally, I added a test case to verify if the grayscale conversion is being done correctly.
Fixes#26276
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videoio: print test params instead of indexes #26948
_videoio_ test names changed - use string instead of index.
E.g. `videoio_read.threads/0` is now `videoio_read.threads/h264_0_RAW`.
It allows to filter tests independently of the platform.
**Notes:**
- not all tests has been updated - only simpler ones and those which have varying parameters depending on platform
Fixed default cap_prop_orientation_auto behaviour #26800
Fixes : #26795
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Open VideoCapture from data stream #25584
### Pull Request Readiness Checklist
Add VideoCapture option to read a raw binary video data from `std::streambuf`.
There are multiple motivations:
1. Avoid disk file creation in case of video already in memory (received by network or from database).
2. Streaming mode. Frames decoding starts during sequential file transfer by chunks.
Suppoted backends:
* FFmpeg
* MSMF (no streaming mode)
Supporter interfaces:
* C++ (std::streambuf)
* Python (io.BufferedIOBase)
resolves https://github.com/opencv/opencv/issues/24400
- [x] test h264
- [x] test IP camera like approach with no metadata but key frame only?
- [x] C API plugin
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Fix VideoCapture fails to read single image with digits in name #26637
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Fix#26457
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videoio: fix cv::VideoWriter with FFmpeg encapsulation timestamps #25874
Fix https://github.com/opencv/opencv/issues/25873 by modifying `cv::VideoWriter` to use provided presentation indices (pts).
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Vibhor
Alexander Smorkalov
Mansour Moufid
Abhishek Gola
Yixuan Tang
Maksim Shabunin
Alex
Andrew Yooeun Chun
Murat Raimbekov
Dmitry Kurtaev
Yan Wen
Sachin Shah
Alexander Alekhin
Francisco Mónica
Skreg
Maxim Smolskiy
Alexander Smorkalov
cudawarped