Tests: fix tests if running with self-built ffmpeg

If self-building ffmpeg from the tag for development reasons, it's
version is set as `n6.1.2` (with n-prefix). This causes failures in
the torchcodec tests. This patch handles such a case accounting
for the `n6.1.2` ffmpeg version format.

Co-authored-by: Dmitry Rogozhkin <[email protected]>
Signed-off-by: Edgar Romo Montiel <[email protected]>

Author: eromomon

test/test_metadata.py

@@ -78,9 +78,7 @@ def test_get_metadata(metadata_getter):
     with pytest.raises(NotImplementedError, match="Decide on logic"):
         metadata.bit_rate
 
-    ffmpeg_major_version = int(
-        get_ffmpeg_library_versions()["ffmpeg_version"].split(".")[0]
-    )
+    ffmpeg_major_version = get_ffmpeg_major_version()
     if ffmpeg_major_version <= 5:
         expected_duration_seconds_from_header = 16.57
         expected_bit_rate_from_header = 324915

test/utils.py

@@ -28,7 +28,10 @@ def cpu_and_cuda():
 
 
 def get_ffmpeg_major_version():
-    return int(get_ffmpeg_library_versions()["ffmpeg_version"].split(".")[0])
+    ffmpeg_version = get_ffmpeg_library_versions()["ffmpeg_version"]
+    if ffmpeg_version.startswith("n"):
+        ffmpeg_version = ffmpeg_version.removeprefix("n")
+    return int(ffmpeg_version.split(".")[0])
 
 
 # For use with decoded data frames. On CPU Linux, we expect exact, bit-for-bit