simple_video_pad

simple_video_pad

Fits a 16:9 video into a 4:3 frame by resizing and padding the picture, using AVBlocks Transcoder with hardcoded input and output file paths.

This sample demonstrates the basic AVBlocks video padding workflow:

1. Initialize the AVBlocks library
2. Create a MediaInfo object to probe the input file
3. Create an input MediaSocket from the probed media info
4. Clone the input socket to start with an identical output configuration
5. Set the output frame size to 640x480 and the display ratio to 4:3
6. Set Pad.Top / Pad.Bottom parameters on the output video pin so the original 16:9 picture is centered and padded to fit the 4:3 frame
7. Set the resize interpolation method to Super for best quality when downscaling
8. Configure a Transcoder with the input and output sockets
9. Run the transcode operation

No command line parsing is used -- the input and output file paths are hardcoded in the source code.

Building

From the repository root:

mkdir -Force -Path build\debug_x64
cd build\debug_x64
cmake -G 'Ninja' -DCMAKE_BUILD_TYPE=debug -DPLATFORM=x64 ../../samples
ninja

The built executable will be placed in bin\x64\simple_video_pad.exe.

Running

1. Download the sample video, the MP4 file from the TED talk video What's the next window into our universe? by Andrew Connolly (Wide 480p, 854x480, 16:9):

   Invoke-WebRequest -Uri "https://archive.org/download/AndrewConnolly_2014/AndrewConnolly_2014.mp4" -OutFile AndrewConnolly_2014.mp4

2. Run the sample from the sample directory (the input/output file paths are relative to the working directory):

   cd samples\windows\simple_video_pad
   ..\..\..\bin\x64\simple_video_pad.exe

3. The padded output file AndrewConnolly_2014_640x480_Padded.mp4 will be created in the samples\windows\simple_video_pad directory.

Notes

• The input file AndrewConnolly_2014.mp4 and output file AndrewConnolly_2014_640x480_Padded.mp4 paths are hardcoded in simple_video_pad.cpp. They are relative to the working directory from which the executable is run.
• If transcoder->open() fails, it may be because AndrewConnolly_2014_640x480_Padded.mp4 already exists in the directory. Delete the output file and try again.
• The source video is 16:9 at 854x480. The output frame is 640x480 (4:3), so the picture is squeezed to 640x270 (640 * 9 / 16) and padded by 105 pixels on top and bottom to preserve the original 16:9 aspect ratio within the 4:3 frame.