Differences

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--- doc:appunti:linux:video:fix_smartphone_portrait_videos [2018/04/07 14:33] – [The ffmpeg Recipe] niccolo
+++ doc:appunti:linux:video:fix_smartphone_portrait_videos [2018/04/07 15:47] (current) – [The Gradient Overlay Mask] niccolo
@@ Line 22: / Line 22: @@
 {{choose_crop_area.png?direct&280 |Choose the crop area}}
-We wrote a **Python script** to assist in step #1, which calculate all the required numbers just provinding two parameters: the **crop_aspect** and the **offset_y**.
+We wrote a **[[#the_python_script|Python script]]** to assist in step #1, which calculate all the required numbers just provinding two parameters: the **crop_aspect** and the **offset_y**.
 Adjust the **crop_aspect** from 0.0 (which selects a square) to 1.0 (which selects the full rectangle of the picture). Using a square-shaped crop area we will get the **highest zoom** level into the video, but we will cut-out  a greather part of the frames, above and below the cropped region.
@@ Line 36: / Line 36: @@
 ===== The Gradient Overlay Mask =====
-When the cropped image is placed above the background, it is quite annoying to see the **sharp edge** of the image. A better approach is to gradually fade the image at the right and at left edges. This requires to blend the image and the background using a **gradient mask**. We prepared the mask as a PNG image, using **convert** by the ImageMagick suite.
+When the cropped image is placed above the background, it is quite annoying to see the **sharp edge** of the image. A better approach is to gradually fade the image at the right and at left edges. This requires to blend the image and the background using a **gradient mask**. We prepared the mask as a **{{gradient_overlay_mask.png?linkonly|PNG image}}**, using **convert** from the ImageMagick suite.
 <code>
@@ Line 47: / Line 47: @@
 </code>
-{{gradient_overlay_mask.png?direct&150|Overlay Mask With Gradient}}
+**NOTICE**: It seems that [[https://www.imagemagick.org/discourse-server/viewtopic.php?f=3&t=33804|there is a bug]] in ImageMagick **gradient:bounding-box**, so we had to generate the mask in top-down mode and rotate it 90 degrees afterward.
 ===== The ffmpeg Recipe =====
@@ Line 61: / Line 60: @@
 <code>
 ffmpeg -i tmp_norotate.mp4 -loop 1 -i tmp_mask.png -filter_complex "\
-[0:v]split [a][b]; \
+  [0:v]split [a][b]; \
-[a]transpose=1,crop=720:720:0:280,scale=768:768,setdar=768/768 [crop]; \
+  [a]transpose=1,crop=720:720:0:280,scale=768:768,setdar=768/768 [crop]; \
-[b]transpose=1,crop=720:720:0:280,scale=1366:768,setdar=16/9,avgblur=54 [back]; \
+  [b]transpose=1,crop=720:720:0:280,scale=1366:768,setdar=16/9,avgblur=54 [back]; \
-[1:v]alphaextract [mask]; \
+  [1:v]alphaextract [mask]; \
-[crop][mask]alphamerge [masked]; \
+  [crop][mask]alphamerge [masked]; \
-[back][masked]overlay=299:0 \
+  [back][masked]overlay=299:0 \
-" video_out.mp4"
+" video_out.mp4
 </code>
 The first video stream **%%[0:v]%%** coming from the video file is splitted in two. The first copy, called **%%[a]%%**, is used to crop the interesting part after the rotation (//transpose//), thus creating the **%%[crop]%%** stream. The second copy, called **%%[b]%%**, is used to create the background applying rotation, stretch and blur filters, thus creating the **%%[back]%%** stream. The mask image is used in loop to create another video stream **%%[1:v]%%**, from which we extract the alpha channel (transparency) creating a stream called **%%[mask]%%**. The **%%[crop]%%** stream is merged with the **%%[mask]%%**, providing the **%%[masked]%%** stream. Finally the **%%[masked]%%** stream is overlayed to the **%%[back]%%** one, to realize the final output.
+===== The Python Script =====
+The Python script **{{smartphonevideo_2landscape.txt|smartphonevideo_2landscape}}** will make the calculation to prepare the whole incantation: it will print on the standard output a **shell script** with the proper invokation of **convert** and **ffmpeg**. Use it in this way:
+<code>
+smartphonevideo_2landscape video_file [crop_aspect] [offset_y] > ffmpeg_recipe
+source ffmpeg_recipe
+</code>
+You have to edit the script to adjust the size of the input video (default 1280x720), the rotation needed (default 1 = 90 deg clockwise), and the size of output video produced (default 1366x768).