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Publier sur MédiaSpip
13 juin 2013Puis-je poster des contenus à partir d’une tablette Ipad ?
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How correctly show video with transparency in Qt with OpenCV + FFMpeg
11 avril 2022, par TheEnigmistI'm trying to show a video with transparency in a Qt6 application using OpenCV + FFMPEG.
Actually those are tool versions :


- 

- Win 11
- Qt 6.3.0
- OpenCV 4.5.5 (built with CMake)
- FFMPEG 2022-04-03-git-1291568c98-full_build-www.gyan.dev










I've used a base .mov video with transparency as test (link provided below).
First of all I've converted .mov video to .webm video (VP9) and I see in output text that alpha channel remains




ffmpeg -i '.\Retro Bars.mov' -c:v libvpx-vp9 -crf 30 -b:v 0 output.webm




Input #0, mov,mp4,m4a,3gp,3g2,mj2,
 ...
 Stream #0:0[0x1](eng): Video: qtrle (rle / 0x20656C72), argb(progressive),
 ...

Output #0, webm, 
 ...
 Stream #0:0(eng): Video: vp9, yuva420p(tv, progressive),
 ...


But when I show info of output file with ffmpeg it loses alpha channel :




ffmpeg -i .\output.webm




Input #0, matroska,webm,
 ...
 Stream #0:0(eng): Video: vp9 (Profile 0), yuv420p(tv, progressive),
 ...


If I open output.webm with OBS it is shown correctly without a background, as shown in picture :



If I try to open it with OpenCV + FFMPEG it shows a black background under bars, as shown in picture :



This is how I load video in Qt :


cv::VideoCapture capture;
capture.open(filename, cv::CAP_FFMPEG);
capture.set(cv::CAP_PROP_CONVERT_RGB, false); // try forcing load alpha channel
... //in a thread
while (capture.read(frame)) {
 qDebug() << "c" << frame.channels() << "t" << frame.type() << "d" << frame.depth(); // output: c 3 t 16 d 0
 cv::cvtColor(frame, frame, cv::COLOR_BGR2RGBA); //useless since no alpha channel is detected
 img = QImage(frame.data, frame.cols, frame.rows, QImage::Format_RGBA8888);
 emit processedImage(img); // to show image in a QLabel with QPixmap::fromImage(img)
}


I think the problem is when I load the video with OpenCV, it doens't detect alpha channel, since I can load correctly in other player (obs, html5, etc.)


What I'm wrong with all process to show this video in Qt with transparency ?


EDIT : Added dropbox link with test video + ffmpeg outputs :
sample items


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ffmpeg "Time code of first frame" not making sense [closed]
23 janvier, par Kevin VaskoI can't seem to make sense of where ffmpeg is coming up with the "Time code of first frame" value.


My original file that I am using.


This video has the general timestamps of the original encoding date (aka the start time of the video the way I understanding it) and a duration of 8 min and 52s


$ mediainfo GL0100002_output.mp4 
General
Complete name : GL0100002_output.mp4
Format : MPEG-4
Format profile : Base Media
Codec ID : isom (isom/iso2/avc1/mp41)
File size : 93.7 MiB
Duration : 8 min 52 s
Overall bit rate : 1 476 kb/s
Encoded date : UTC 2022-02-23 15:18:42
Tagged date : UTC 2022-02-23 15:18:42
Writing application : Lavf58.29.100

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L3
Format settings : CABAC / 4 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference frames : 4 frames
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 8 min 52 s
Bit rate : 1 342 kb/s
Width : 848 pixels
Height : 480 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 23.976 (24000/1001) FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.138
Stream size : 85.2 MiB (91%)
Title : GoPro AVC 
Writing library : x264 core 155 r2917 0a84d98
Encoding settings : cabac=1 / ref=3 / deblock=1:0:0 / analyse=0x3:0x113 / me=hex / subme=7 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=1 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-2 / threads=12 / lookahead_threads=2 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=1 / weightb=1 / open_gop=0 / weightp=2 / keyint=250 / keyint_min=23 / scenecut=40 / intra_refresh=0 / rc_lookahead=40 / rc=crf / mbtree=1 / crf=23.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
Language : English
Encoded date : UTC 2022-02-23 15:18:42
Tagged date : UTC 2022-02-23 15:18:42
Color range : Full
Codec configuration box : avcC

Audio
ID : 2
Format : AAC LC
Format/Info : Advanced Audio Codec Low Complexity
Codec ID : mp4a-40-2
Duration : 8 min 52 s
Bit rate mode : Constant
Bit rate : 129 kb/s
Channel(s) : 2 channels
Channel layout : L R
Sampling rate : 48.0 kHz
Frame rate : 46.875 FPS (1024 SPF)
Compression mode : Lossy
Stream size : 8.16 MiB (9%)
Title : GoPro AAC 
Language : English
Default : Yes
Alternate group : 1
Encoded date : UTC 2022-02-23 15:18:42
Tagged date : UTC 2022-02-23 15:18:42

Other
ID : 3
Type : Time code
Format : QuickTime TC
Duration : 8 min 52 s
Frame rate : 23.976 (24000/1001) FPS
Time code of first frame : 15:57:41:15
Time code, striped : Yes
Title : GoPro AVC 
Language : English
Default : No
Encoded date : UTC 2022-02-23 15:18:42
Tagged date : UTC 2022-02-23 15:18:42


Now if I run


ffmpeg -y -nostdin -v error -ss 00:00:00.042 -i GL0100002_output.mp4 -t 00:00:25.192 -map 0 -map -0:d -c:v libx264 -preset fast -crf 21 -c:a aac -sn GL0100002_test.DSME_0001.mp4

I get the following mediainfo


$ mediainfo GL0100002_test.DSME_0001.mp4 
General
Complete name : GL0100002_test.DSME_0001.mp4
Format : MPEG-4
Format profile : Base Media
Codec ID : isom (isom/iso2/avc1/mp41)
File size : 4.54 MiB
Duration : 25 s 234 ms
Overall bit rate : 1 510 kb/s
Writing application : Lavf58.29.100

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L3
Format settings : CABAC / 4 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference frames : 4 frames
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 25 s 234 ms
Bit rate : 1 376 kb/s
Width : 848 pixels
Height : 480 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 23.976 (24000/1001) FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.141
Stream size : 4.14 MiB (91%)
Title : GoPro AVC 
Writing library : x264 core 155 r2917 0a84d98
Encoding settings : cabac=1 / ref=2 / deblock=1:0:0 / analyse=0x3:0x113 / me=hex / subme=6 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=1 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-2 / threads=12 / lookahead_threads=2 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=1 / weightb=1 / open_gop=0 / weightp=1 / keyint=250 / keyint_min=23 / scenecut=40 / intra_refresh=0 / rc_lookahead=30 / rc=crf / mbtree=1 / crf=21.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
Language : English
Color range : Full
Codec configuration box : avcC

Audio
ID : 2
Format : AAC LC
Format/Info : Advanced Audio Codec Low Complexity
Codec ID : mp4a-40-2
Duration : 25 s 214 ms
Duration_LastFrame : -3 ms
Bit rate mode : Constant
Bit rate : 129 kb/s
Channel(s) : 2 channels
Channel layout : L R
Sampling rate : 48.0 kHz
Frame rate : 46.875 FPS (1024 SPF)
Compression mode : Lossy
Stream size : 398 KiB (9%)
Title : GoPro AAC 
Language : English
Default : Yes
Alternate group : 1

Other
ID : 3
Type : Time code
Format : QuickTime TC
Duration : 25 s 234 ms
Frame rate : 23.976 (24000/1001) FPS
Time code of first frame : 15:57:41:15
Time code, striped : Yes
Title : GoPro AVC 
Language : English
Default : No


But what I don't understand is where
Time code of first frameis coming from. I would expect it would be00:00:00.042or evenUTC 2022-02-23 15:18:42+ .042 but appear to be.

Time code of first frame : 15:57:41:15


Is this potentially clobbering together something to get this time that isn't obvious ?


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Two character glob pattern
18 octobre 2022, par eSlavkoI have camera capturing image every 10 seconds and store in folder with image name as timestamp like

/2022-05-10_19:11:50.jpg
Each week is stored in separate folder.
Now I want to make video from that images using ffmpeg.
It works with images declared as-pattern_type glob -i "*.jpg"Now I want to make video from images captured only in daytime. For example from images/2022-05-10_XX:11:50.jpgwhereXXis in range from 05, 06, 07 .. 20, 21. I try with glob patterns but seems that it can work only over single digit.

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