Add trim parameter to av_video_images()

Fixes #59

.github/workflows/R-CMD-check.yaml

@@ -50,3 +50,5 @@ jobs:
           needs: check
 
       - uses: r-lib/actions/check-r-package@v2
+        with:
+          args: 'c("--no-manual", "--as-cran", "--run-dontrun")'

DESCRIPTION

@@ -14,7 +14,7 @@ URL: https://ropensci.r-universe.dev/av,
     https://docs.ropensci.org/av/
 BugReports: https://github.com/ropensci/av/issues
 Encoding: UTF-8
-RoxygenNote: 7.3.1
+RoxygenNote: 7.3.2
 Roxygen: list(markdown = TRUE)
 SystemRequirements: FFmpeg (>= 3.2); with at least libx264 and lame (mp3) drivers.
 	MacOS Homebrew: ffmpeg. Debian/Ubuntu: libavfilter-dev. Fedora/RHEL: either 
@@ -24,6 +24,7 @@ Depends: R (>= 3.5)
 Imports: graphics
 Config/pkgdown: seewave, ggplot2, phonTools, signal, tuneR
 Suggests: 
+    curl,
     testthat,
     ps,
     ggplot2,

NEWS

@@ -1,6 +1,8 @@
 0.9.4
   - Windows: use ffmpeg from Rtools when available
   - Relax unit tests for libavfilter-free-devel on RedHat/Fedora
+  - av_video_images() gains a trim parameter
+  - Some internal fixes to support trim filters
 
 0.9.3
   - Fixes for ffmpeg 7.1

R/images.R

@@ -12,10 +12,20 @@
 #' @param video an input video
 #' @param destdir directory where to save the png files
 #' @param fps sample rate of images. Use `NULL` to get all images.
+#' @param trim string value for [ffmpeg trim filter](https://ffmpeg.org/ffmpeg-filters.html#trim)
+#' for example `"10:15"` for seconds or `"start_frame=100:end_frame=110"` for frames.
 #' @param format image format such as `png` or `jpeg`, must be available from `av_encoders()`
-av_video_images <- function(video, destdir = tempfile(), format = 'jpg', fps = NULL){
+#' @examples \dontrun{
+#' curl::curl_download('https://jeroen.github.io/images/blackbear.mp4', 'blackbear.mp4')
+#' av_video_images('blackbear.mp4', fps = 1, trim = "10:20")
+#' }
+av_video_images <- function(video, destdir = tempfile(), format = 'jpg', fps = NULL, trim = NULL){
   stopifnot(length(video) == 1)
-  vfilter <- ifelse(length(fps), paste0('fps=fps=', fps), 'null')
+  filter_fps <- if(length(fps)) paste0('fps=fps=', fps)
+  filter_trim <- if(length(trim)) paste0('trim=', trim)
+  vfilter <- paste(c(filter_trim, filter_fps), collapse = ', ')
+  if(vfilter == "")
+    vfilter <- 'null'
   framerate <- av_media_info(video)$video$framerate
   dir.create(destdir)
   codec <- switch(format, jpeg = 'mjpeg', jpg = 'mjpeg', format)

av.Rproj

@@ -1,4 +1,5 @@
 Version: 1.0
+ProjectId: 653ad251-3091-4d6a-9c2a-9ef1fbb435bf
 
 RestoreWorkspace: Default
 SaveWorkspace: Default

src/video.c

@@ -512,9 +512,9 @@ static int encode_output_frames(output_container *output){
     if(ret == AVERROR(EAGAIN))
       return 0;
     if(ret == AVERROR_EOF){
-      output->early_end = 1; //trim filter can EOF before input is fully drained
       bail_if_null(output, "filter did not return any frames");
       bail_if(avcodec_send_frame(output->video_encoder, NULL), "avcodec_send_frame (flush video)");
+      output->early_end = 1; //trim filter can EOF before input is fully drained
     } else {
       bail_if(ret, "av_buffersink_get_frame");
       if(output->muxer == NULL)