Add new (4.0+) API for av_[de]muxer_iterate (#52)

* Add new MuxerIter/DemuxerIter for 4.0+

* Add Default impls for MuxerIter/DemuxerIter

* Add tests for MuxerIter/DemuxerIter

* Use mutable reference over addr_of_mut!

* Don't dereference long_name if nullptr

This happens if FFmpeg is configured with `--enable-small`

src/format/format/input.rs

@@ -27,7 +27,15 @@ impl Input {
     }
 
     pub fn description(&self) -> &str {
-        unsafe { from_utf8_unchecked(CStr::from_ptr((*self.as_ptr()).long_name).to_bytes()) }
+        unsafe {
+            let long_name = (*self.as_ptr()).long_name;
+
+            if long_name.is_null() {
+                ""
+            } else {
+                from_utf8_unchecked(CStr::from_ptr(long_name).to_bytes())
+            }
+        }
     }
 
     pub fn extensions(&self) -> Vec<&str> {

src/format/format/mod.rs

@@ -12,6 +12,11 @@ mod iter;
 #[cfg(not(feature = "ffmpeg_5_0"))]
 pub use self::iter::Iter;
 
+#[cfg(feature = "ffmpeg_4_0")]
+mod new_iter;
+#[cfg(feature = "ffmpeg_4_0")]
+pub use self::new_iter::{DemuxerIter, MuxerIter};
+
 pub enum Format {
     Input(Input),
     Output(Output),
@@ -51,3 +56,13 @@ impl Format {
 pub fn list() -> Iter {
     Iter::new()
 }
+
+#[cfg(feature = "ffmpeg_4_0")]
+pub fn list_demuxers() -> DemuxerIter {
+    DemuxerIter::new()
+}
+
+#[cfg(feature = "ffmpeg_4_0")]
+pub fn list_muxers() -> MuxerIter {
+    MuxerIter::new()
+}

src/format/format/new_iter.rs

@@ -0,0 +1,93 @@
+use std::ptr::null_mut;
+
+use crate::ffi::*;
+use crate::format::format::{Input, Output};
+use crate::format::Format;
+use libc::c_void;
+
+pub struct DemuxerIter {
+    ptr: *mut c_void,
+}
+
+impl DemuxerIter {
+    pub fn new() -> Self {
+        Self { ptr: null_mut() }
+    }
+}
+
+impl Default for DemuxerIter {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl Iterator for DemuxerIter {
+    type Item = Format;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        unsafe {
+            let next = av_demuxer_iterate(&mut self.ptr);
+            if next.is_null() {
+                None
+            } else {
+                Some(Format::Input(Input::wrap(next as _)))
+            }
+        }
+    }
+}
+
+pub struct MuxerIter {
+    ptr: *mut c_void,
+}
+
+impl MuxerIter {
+    pub fn new() -> Self {
+        Self { ptr: null_mut() }
+    }
+}
+
+impl Default for MuxerIter {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl Iterator for MuxerIter {
+    type Item = Format;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        unsafe {
+            let next = av_muxer_iterate(&mut self.ptr);
+            if next.is_null() {
+                None
+            } else {
+                Some(Format::Output(Output::wrap(next as _)))
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn muxer_iter() {
+        for f in MuxerIter::new() {
+            println!("{}:", f.name());
+            println!("\t{}", f.description());
+            println!("\t{:?}", f.extensions());
+            println!("\t{:?}", f.mime_types());
+        }
+    }
+
+    #[test]
+    fn demuxer_iter() {
+        for f in DemuxerIter::new() {
+            println!("{}:", f.name());
+            println!("\t{}", f.description());
+            println!("\t{:?}", f.extensions());
+            println!("\t{:?}", f.mime_types());
+        }
+    }
+}

src/format/format/output.rs

@@ -32,7 +32,15 @@ impl Output {
     }
 
     pub fn description(&self) -> &str {
-        unsafe { from_utf8_unchecked(CStr::from_ptr((*self.as_ptr()).long_name).to_bytes()) }
+        unsafe {
+            let long_name = (*self.as_ptr()).long_name;
+
+            if long_name.is_null() {
+                ""
+            } else {
+                from_utf8_unchecked(CStr::from_ptr(long_name).to_bytes())
+            }
+        }
     }
 
     pub fn extensions(&self) -> Vec<&str> {