screenshot: change details of --screenshot-format handling

This is just a pointless refactor with the only goal of making
image_writer_opts.format a number.

The pointless part of it is that instead of using some sort of arbitrary
ID (in place of a file extension string), we use a AV_CODEC_ID_. There
was also some idea of falling back to the libavcodec MJPEG encoder if
mpv was not linked against libjpeg, but this fails. libavcodec insist on
having AV_PIX_FMT_YUVJ420P, which we pretend does not exist, and which
we always map to AV_PIX_FMT_YUV420P (without the J indicating full
range), so encoder init fails. This is pretty dumb, but whatever. The
not-caring factor is raised by the fact that we don't know that we
should convert to full range, because encoders have no proper way to
signal this. (Be reminded that AV_PIX_FMT_YUVJ420P is deprecated.)

1 files changed, 4 insertions, 1 deletions

diff --git a/video/image_writer.h b/video/image_writer.h
index 8b7414b62a..723dffc3ef 100644
--- a/video/image_writer.h
+++ b/video/image_writer.h
@@ -21,7 +21,7 @@ struct mp_image;
 struct mp_log;
 
 struct image_writer_opts {
-    char *format;
+    int format;
     int high_bit_depth;
     int png_compression;
     int png_filter;
@@ -42,6 +42,9 @@ extern const struct m_option image_writer_opts[];
 // Return the file extension that will be used, e.g. "png".
 const char *image_writer_file_ext(const struct image_writer_opts *opts);
 
+// Map file extension to format ID - return 0 (which is invalid) if unknown.
+int image_writer_format_from_ext(const char *ext);
+
 /*
  * Save the given image under the given filename. The parameters csp and opts
  * are optional. All pixel formats supported by swscale are supported.