vflip fliter throws an exception on FFmpegFrameFilter

[SIY1121]

Hi
I have one bug report and question.

I'm using javacv as FFmpeg wrapper.
I received raw video frames and tried to flip frames when encoding, but using vflip fliter throws an exception.

java.lang.IllegalArgumentException
	at java.nio.Buffer.limit(Buffer.java:275)
	at org.bytedeco.javacv.FFmpegFrameFilter.pull(FFmpegFrameFilter.java:359)

On debugging,I identified the cause.
With vflip filter, the imageStride of the frame returned by ffmpeg will be negative.

javacv/src/main/java/org/bytedeco/javacv/FFmpegFrameFilter.java

Lines 582 to 588 in 51c5714

	if (ptr != null && !ptr.equals(image_ptr[0])) {
	image_ptr[0] = ptr.capacity(frame.imageHeight * frame.imageStride);
	image_buf[0] = ptr.asBuffer();
	}
	frame.image = image_buf;
	frame.image[0].position(0).limit(frame.imageHeight * frame.imageStride);
	frame.imageChannels = frame.imageStride / frame.imageWidth;

This process doesn't seem to consider it.
So I changed code to use absolute value and it works fine.

if (ptr != null && !ptr.equals(image_ptr[0])) { 
     image_ptr[0] = ptr.capacity(frame.imageHeight * Math.abs(frame.imageStride)); 
     image_buf[0] = ptr.asBuffer(); 
 } 
 frame.image = image_buf; 
 frame.image[0].position(0).limit(frame.imageHeight *  Math.abs(frame.imageStride)); 
 frame.imageChannels = frame.imageStride / Math.abs(frame.imageWidth);

I didn't use OpenCV flip function because process of converting array to mat and converting it to FFmpeg frame looks inefficiency.
Was it good choice?

Thank you.

[saudet]

Hum, interesting. Sounds like a bug in FFmpeg, but anyway, could you send a pull request to fix this in JavaCV? Thanks!

[saudet]

Fixed with pull #977, thanks!

[saudet]

Which has now been integrated in version 1.4.2. Thanks again for the fix!