Read FFprobe's answer without spawning FFprobe (#195)

readMediaInformation was 114 missed instructions and 24 missed branches -- the second
largest block on the wave-4 report -- and exactly one line of it needed a device:

    FFprobeKit.getMediaInformation(path).getMediaInformation()

Everything after it reads an ordinary object, so it moves into ffprobeInfoFrom and the edge
keeps the call and the null check. Verified JVM-safe rather than assumed: javap over the
committed AAR's runtime jar shows MediaInformation(JSONObject, List<StreamInformation>,
List<Chapter>) and StreamInformation(JSONObject) as plain public constructors whose <clinit>
does not load the native library, so a test builds its own without libffmpegkit present.

The decision worth reaching is containerFrom's SECOND argument. FFprobe reports
"matroska,webm" for both MKV and WebM because they share a demuxer, so the video codec is
the only thing separating them. containerFrom has thirty-three covered branches and not one
can notice that argument being dropped -- the mistake is at the call, not in the callee, so
every existing containerFrom test stays green while every VP9 WebM quietly becomes an MKV.

Two things the tests found rather than confirmed.

The format properties are NESTED under "format": getFormat() resolves through
getStringFormatProperty, not off the top-level object. The first fixture put the keys at the
top level and four cases failed with a null container. The helper says so now.

And one mutation SURVIVED on the first pass -- reading dimensions with
streams.firstNotNullOfOrNull { it.getWidth() } instead of video?.getWidth(). The fixture put
the dimensions on the chosen video stream, which is also the first stream carrying any, so
the two readings agreed and the test could not tell them apart. Separating them needs a
chosen video stream with NO dimensions and a later one that has them, which is a real shape:
FFprobe omits width/height for a stream it could not measure. That case is now its own test
and the mutation reddens it.

Mutations, each run and restored:

  drop the video codec argument to containerFrom        1 red
  take the LAST video stream instead of the first       1 red
  read dimensions from any stream, not the chosen one   0 red -> 1 red after the new case
  let an unparseable duration throw instead of zero     1 red

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

app/src/main/java/org/libremediaconverter/convert/MediaProbe.kt

@@ -221,12 +221,39 @@ object MediaProbe {
         null
     }
 
-    private fun readMediaInformation(path: String): FFprobeInfo? {
-        // ffmpeg-kit-next is compiled from Kotlin with private backing fields, so these have to go
-        // through the Java getters rather than property syntax.
-        val info: MediaInformation = FFprobeKit.getMediaInformation(path).getMediaInformation()
-            ?: return null
+    /**
+     * The thin edge: spawn FFprobe, hand what it said to [ffprobeInfoFrom].
+     *
+     * Everything device-bound is on this line and the null check under it. What FFprobe *said* is a
+     * `MediaInformation`, which is an ordinary object over a `JSONObject` — so the reading of it is
+     * a decision a test can choose the inputs for, and it lives below rather than here.
+     */
+    private fun readMediaInformation(path: String): FFprobeInfo? =
+        FFprobeKit.getMediaInformation(path).getMediaInformation()?.let(::ffprobeInfoFrom)
 
+    /**
+     * What FFprobe's answer means, as a function of the answer alone.
+     *
+     * `internal` for the same reason [Extracted] and [FFprobeInfo] are: a test cannot name it
+     * otherwise, and the JVM test source set is a friend of `main`.
+     *
+     * **JVM-safe, verified rather than assumed.** `javap` over the committed AAR's runtime jar:
+     * `MediaInformation(JSONObject, List<StreamInformation>, List<Chapter>)` and
+     * `StreamInformation(JSONObject)` are plain public constructors, and neither class's `<clinit>`
+     * touches the native library — so a test builds its own without `libffmpegkit` being present.
+     * That is the whole reason this split is worth making: `readMediaInformation` was 114 missed
+     * instructions and 24 missed branches, of which exactly one line needed a device.
+     *
+     * The subtle part is the **second argument to [containerFrom]**. `matroska,webm` is reported
+     * for both MKV and WebM — they share a demuxer — so the video codec is the only thing that
+     * separates them, and dropping it silently turns every VP9 WebM into an MKV. `containerFrom`
+     * has thirty-three covered branches of its own and none of them can notice that, because the
+     * mistake is at the call rather than in the callee.
+     *
+     * ffmpeg-kit-next is compiled from Kotlin with private backing fields, so these go through the
+     * Java getters rather than property syntax.
+     */
+    internal fun ffprobeInfoFrom(info: MediaInformation): FFprobeInfo {
         val streams = info.getStreams().orEmpty()
         val video = streams.firstOrNull { it.getType() == "video" }
         val audio = streams.firstOrNull { it.getType() == "audio" }