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Added alpha channel support to VideoWriter and VideoCapture.

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This commit is contained in:
Alexander Smorkalov
2026-04-02 15:15:37 +03:00
parent 10e32c96f5
commit 87bdcd4f14
3 changed files with 120 additions and 7 deletions
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modules/videoio/src/cap_ffmpeg_impl.hpp
+49 -6
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@@ -612,6 +612,7 @@ struct CvCapture_FFMPEG
bool rawModeInitialized;
bool rawSeek;
bool convertRGB;
bool enableAlpha;
AVPacket packet_filtered;
#if LIBAVFORMAT_BUILD >= CALC_FFMPEG_VERSION(58, 20, 100)
AVBSFContext* bsfc;
@@ -669,6 +670,7 @@ void CvCapture_FFMPEG::init()
rawModeInitialized = false;
rawSeek = false;
convertRGB = true;
enableAlpha = false;
memset(&packet_filtered, 0, sizeof(packet_filtered));
av_init_packet(&packet_filtered);
bsfc = NULL;
@@ -1085,9 +1087,10 @@ bool CvCapture_FFMPEG::open(const char* _filename, int index, const Ptr<IStreamR
CV_LOG_WARNING(NULL, "VIDEOIO/FFMPEG: BGR conversion turned OFF, decoded frame will be "
"returned in its original format. "
"Multiplanar formats are not supported by the backend. "
"Only GRAY8/GRAY16LE pixel formats have been tested. "
"Only GRAY8/GRAY16LE/RGBA pixel formats have been tested. "
"Use at your own risk.");
}
if (params.has(CAP_PROP_FORMAT))
{
int value = params.get<int>(CAP_PROP_FORMAT);
@@ -1098,8 +1101,19 @@ bool CvCapture_FFMPEG::open(const char* _filename, int index, const Ptr<IStreamR
}
else
{
CV_LOG_ERROR(NULL, "VIDEOIO/FFMPEG: CAP_PROP_FORMAT parameter value is invalid/unsupported: " << value);
return false;
if (value == CV_8UC3)
{
enableAlpha = false;
}
if (value == CV_8UC4)
{
enableAlpha = true;
}
else
{
CV_LOG_ERROR(NULL, "VIDEOIO/FFMPEG: CAP_PROP_FORMAT parameter value is invalid/unsupported: " << value);
return false;
}
}
}
if(!rawMode) {
@@ -1879,9 +1893,12 @@ bool CvCapture_FFMPEG::retrieveFrame(int flag, unsigned char** data, int* step,
<< ", primaries: " << av_color_primaries_name(sw_picture->color_primaries)
<< ", transfer: " << av_color_transfer_name(sw_picture->color_trc)
);
const AVPixelFormat result_format = convertRGB ? AV_PIX_FMT_BGR24 : (AVPixelFormat)sw_picture->format;
const AVPixelFormat color_format = enableAlpha ? AV_PIX_FMT_BGRA : AV_PIX_FMT_BGR24;
const AVPixelFormat result_format = convertRGB ? color_format : (AVPixelFormat)sw_picture->format;
switch (result_format)
{
case AV_PIX_FMT_BGRA: *depth = CV_8U; *cn = 4; break;
case AV_PIX_FMT_BGR24: *depth = CV_8U; *cn = 3; break;
case AV_PIX_FMT_GRAY8: *depth = CV_8U; *cn = 1; break;
case AV_PIX_FMT_GRAY16LE: *depth = CV_16U; *cn = 1; break;
@@ -2122,6 +2139,12 @@ double CvCapture_FFMPEG::getProperty( int property_id ) const
case CAP_PROP_FORMAT:
if (rawMode)
return -1;
else if (!convertRGB)
return CV_8UC1;
else if (enableAlpha)
return CV_8UC4;
else
return CV_8UC3;
break;
case CAP_PROP_CONVERT_RGB:
return convertRGB;
@@ -2365,8 +2388,20 @@ bool CvCapture_FFMPEG::setProperty( int property_id, double value )
seek((int64_t)(value*ic->duration));
return true;
case CAP_PROP_FORMAT:
if (!convertRGB)
return false;
if (value == -1)
return setRaw();
else if (value == CV_8UC3)
{
enableAlpha = false;
return true;
}
else if (value == CV_8UC4)
{
enableAlpha = true;
return true;
}
return false;
case CAP_PROP_CONVERT_RGB:
convertRGB = (value != 0);
@@ -2775,6 +2810,12 @@ bool CvVideoWriter_FFMPEG::writeFrame( const unsigned char* data, int step, int
return false;
}
}
else if (input_pix_fmt == AV_PIX_FMT_BGRA) {
if (cn != 4) {
CV_LOG_WARNING(NULL, "write frame skipped - expected 4 channels but got " << cn);
return false;
}
}
else if (input_pix_fmt == AV_PIX_FMT_GRAY8 || input_pix_fmt == AV_PIX_FMT_GRAY16LE) {
if (cn != 1) {
CV_LOG_WARNING(NULL, "write frame skipped - expected 1 channel but got " << cn);
@@ -3151,6 +3192,8 @@ bool CvVideoWriter_FFMPEG::open( const char * filename, int fourcc,
use_opencl = params.get<int>(VIDEOWRITER_PROP_HW_ACCELERATION_USE_OPENCL);
}
bool enable_alpha = params.get<bool>(VIDEOWRITER_PROP_ENABLE_ALPHA, false);
if (params.warnUnusedParameters())
{
CV_LOG_ERROR(NULL, "VIDEOIO/FFMPEG: unsupported parameters in VideoWriter, see logger INFO channel for details");
@@ -3185,7 +3228,7 @@ bool CvVideoWriter_FFMPEG::open( const char * filename, int fourcc,
{
switch (depth)
{
case CV_8U: input_pix_fmt = AV_PIX_FMT_BGR24; break;
case CV_8U: input_pix_fmt = enable_alpha ? AV_PIX_FMT_BGRA : AV_PIX_FMT_BGR24; break;
default:
CV_LOG_WARNING(NULL, "Unsupported input depth for color image: " << depth);
return false;
@@ -3387,7 +3430,7 @@ bool CvVideoWriter_FFMPEG::open( const char * filename, int fourcc,
break;
default:
// good for lossy formats, MPEG, etc.
codec_pix_fmt = AV_PIX_FMT_YUV420P;
codec_pix_fmt = enable_alpha ? AV_PIX_FMT_YUVA420P : AV_PIX_FMT_YUV420P;
break;
}