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videoio: avoid false-positive unsupported mode warning on capture failure (#26519)

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In VideoCapture::open(), PR #22700 added checks to log warnings when a requested
backend cannot perform a capture mode (e.g. capturing by index with CAP_FFMPEG).
However, the condition only tested if (isBackendBuiltIn(apiPreference)), which
evaluates to true for all built-in backends regardless of whether they support the mode.

As a result, whenever a camera or file failed to open (e.g., camera not connected,
invalid camera index, missing or unreadable file), OpenCV emitted false-positive
warnings:
- VIDEOIO(V4L2): backend is generally available but can't be used to capture by index
- VIDEOIO(FFMPEG): backend is generally available but can't be used to capture by name
even though V4L2 and FFMPEG natively support those respective modes.

Track whether apiPreference matches an available backend for the requested mode in
getAvailableBackends_CaptureByIndex, getAvailableBackends_CaptureByFilename, and
getAvailableBackends_CaptureByStream. Only log the warning when the backend is
genuinely absent from the supported list for that mode while being available on the system.

Resolves #26519

Signed-off-by: paneendrakumar0 <paneendra100@gmail.com>
This commit is contained in:
paneendrakumar0
2026-10-21 15:14:33 +05:30
parent f2be0a0a28
commit 0a5c96c832
1 changed files with 27 additions and 9 deletions
Download Patch File Download Diff File Expand all files Collapse all files

36
modules/videoio/src/cap.cpp
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@@ -124,12 +124,17 @@ bool VideoCapture::open(const String& filename, int apiPreference, const std::ve
}
const VideoCaptureParameters parameters(params);
bool backendSupportsMode = false;
const std::vector<VideoBackendInfo> backends = cv::videoio_registry::getAvailableBackends_CaptureByFilename();
for (size_t i = 0; i < backends.size(); i++)
{
const VideoBackendInfo& info = backends[i];
if (apiPreference == CAP_ANY || apiPreference == info.id)
{
if (apiPreference == info.id)
{
backendSupportsMode = true;
}
if (!info.backendFactory)
{
CV_LOG_DEBUG(NULL, "VIDEOIO(" << info.name << "): factory is not available (plugins require filesystem support)");
@@ -204,9 +209,10 @@ bool VideoCapture::open(const String& filename, int apiPreference, const std::ve
}
}
if(apiPreference != CAP_ANY)
if (apiPreference != CAP_ANY && !backendSupportsMode)
{
bool found = cv::videoio_registry::isBackendBuiltIn(static_cast<VideoCaptureAPIs>(apiPreference));
bool found = cv::videoio_registry::hasBackend(static_cast<VideoCaptureAPIs>(apiPreference)) ||
cv::videoio_registry::isBackendBuiltIn(static_cast<VideoCaptureAPIs>(apiPreference));
if (found)
{
CV_LOG_WARNING(NULL, cv::format("VIDEOIO(%s): backend is generally available "
@@ -252,12 +258,14 @@ bool VideoCapture::open(const Ptr<IStreamReader>& stream, int apiPreference, con
}
const VideoCaptureParameters parameters(params);
bool backendSupportsMode = false;
const std::vector<VideoBackendInfo> backends = cv::videoio_registry::getAvailableBackends_CaptureByStream();
for (size_t i = 0; i < backends.size(); i++)
{
const VideoBackendInfo& info = backends[i];
if (apiPreference != info.id)
continue;
backendSupportsMode = true;
if (!info.backendFactory)
{
@@ -332,12 +340,16 @@ bool VideoCapture::open(const Ptr<IStreamReader>& stream, int apiPreference, con
}
}
bool found = cv::videoio_registry::isBackendBuiltIn(static_cast<VideoCaptureAPIs>(apiPreference));
if (found)
if (apiPreference != CAP_ANY && !backendSupportsMode)
{
CV_LOG_WARNING(NULL, cv::format("VIDEOIO(%s): backend is generally available "
"but can't be used to capture by read data stream",
cv::videoio_registry::getBackendName(static_cast<VideoCaptureAPIs>(apiPreference)).c_str()));
bool found = cv::videoio_registry::hasBackend(static_cast<VideoCaptureAPIs>(apiPreference)) ||
cv::videoio_registry::isBackendBuiltIn(static_cast<VideoCaptureAPIs>(apiPreference));
if (found)
{
CV_LOG_WARNING(NULL, cv::format("VIDEOIO(%s): backend is generally available "
"but can't be used to capture by read data stream",
cv::videoio_registry::getBackendName(static_cast<VideoCaptureAPIs>(apiPreference)).c_str()));
}
}
if (throwOnFail)
@@ -387,12 +399,17 @@ bool VideoCapture::open(int cameraNum, int apiPreference, const std::vector<int>
}
const VideoCaptureParameters parameters(params);
bool backendSupportsMode = false;
const std::vector<VideoBackendInfo> backends = cv::videoio_registry::getAvailableBackends_CaptureByIndex();
for (size_t i = 0; i < backends.size(); i++)
{
const VideoBackendInfo& info = backends[i];
if (apiPreference == CAP_ANY || apiPreference == info.id)
{
if (apiPreference == info.id)
{
backendSupportsMode = true;
}
if (!info.backendFactory)
{
CV_LOG_DEBUG(NULL, "VIDEOIO(" << info.name << "): factory is not available (plugins require filesystem support)");
@@ -467,9 +484,10 @@ bool VideoCapture::open(int cameraNum, int apiPreference, const std::vector<int>
}
}
if(apiPreference != CAP_ANY)
if (apiPreference != CAP_ANY && !backendSupportsMode)
{
bool found = cv::videoio_registry::isBackendBuiltIn(static_cast<VideoCaptureAPIs>(apiPreference));
bool found = cv::videoio_registry::hasBackend(static_cast<VideoCaptureAPIs>(apiPreference)) ||
cv::videoio_registry::isBackendBuiltIn(static_cast<VideoCaptureAPIs>(apiPreference));
if (found)
{
CV_LOG_WARNING(NULL, cv::format("VIDEOIO(%s): backend is generally available "