[ffmpeg] Framework for feature detection

Related: #1502, #1237, https://github.com/ytdl-org/youtube-dl/pull/29581

yt_dlp/__init__.py

@@ -232,7 +232,8 @@ def parse_retries(retries, name=''):
             parser.error('invalid audio format specified')
     if opts.audioquality:
         opts.audioquality = opts.audioquality.strip('k').strip('K')
-        if int_or_none(float_or_none(opts.audioquality)) is None:  # int_or_none prevents inf, nan
+        audioquality = int_or_none(float_or_none(opts.audioquality))  # int_or_none prevents inf, nan
+        if audioquality is None or audioquality < 0:
             parser.error('invalid audio quality specified')
     if opts.recodevideo is not None:
         opts.recodevideo = opts.recodevideo.replace(' ', '')

yt_dlp/postprocessor/ffmpeg.py

@@ -16,7 +16,8 @@
     encodeArgument,
     encodeFilename,
     float_or_none,
-    get_exe_version,
+    _get_exe_version_output,
+    detect_exe_version,
     is_outdated_version,
     ISO639Utils,
     orderedSet,
@@ -80,10 +81,10 @@ def get_versions(downloader=None):
 
     def _determine_executables(self):
         programs = ['avprobe', 'avconv', 'ffmpeg', 'ffprobe']
-        prefer_ffmpeg = True
 
-        def get_ffmpeg_version(path):
-            ver = get_exe_version(path, args=['-version'])
+        def get_ffmpeg_version(path, prog):
+            out = _get_exe_version_output(path, ['-bsfs'])
+            ver = detect_exe_version(out) if out else False
             if ver:
                 regexs = [
                     r'(?:\d+:)?([0-9.]+)-[0-9]+ubuntu[0-9.]+$',  # Ubuntu, see [1]
@@ -94,17 +95,23 @@ def get_ffmpeg_version(path):
                     mobj = re.match(regex, ver)
                     if mobj:
                         ver = mobj.group(1)
-            return ver
+            self._versions[prog] = ver
+            if prog != 'ffmpeg' or not out:
+                return
+
+            # TODO: Feature detection
 
         self.basename = None
         self.probe_basename = None
-
         self._paths = None
         self._versions = None
-        if self._downloader:
+        self._features = {}
+
         prefer_ffmpeg = self.get_param('prefer_ffmpeg', True)
         location = self.get_param('ffmpeg_location')
-            if location is not None:
+        if location is None:
+            self._paths = {p: p for p in programs}
+        else:
             if not os.path.exists(location):
                 self.report_warning(
                     'ffmpeg-location %s does not exist! '
@@ -124,12 +131,10 @@ def get_ffmpeg_version(path):
                 (p, os.path.join(dirname, p)) for p in programs)
             if basename:
                 self._paths[basename] = location
-                self._versions = dict(
-                    (p, get_ffmpeg_version(self._paths[p])) for p in programs)
-        if self._versions is None:
-            self._versions = dict(
-                (p, get_ffmpeg_version(p)) for p in programs)
-            self._paths = dict((p, p) for p in programs)
+
+        self._versions = {}
+        for p in programs:
+            get_ffmpeg_version(self._paths[p], p)
 
         if prefer_ffmpeg is False:
             prefs = ('avconv', 'ffmpeg')
@@ -382,7 +387,9 @@ def _quality_args(self, codec):
 
         limits = {
             'libmp3lame': (10, 0),
-            'aac': (0.1, 11),
+            # FFmpeg's AAC encoder does not have an upper limit for the value of -q:a.
+            # Experimentally, with values over 4, bitrate changes were minimal or non-existent
+            'aac': (0.1, 4),
             'vorbis': (0, 10),
             'opus': None,  # doesn't support -q:a
             'wav': None,

yt_dlp/utils.py

@@ -4007,10 +4007,7 @@ def check_executable(exe, args=[]):
     return exe
 
 
-def get_exe_version(exe, args=['--version'],
-                    version_re=None, unrecognized='present'):
-    """ Returns the version of the specified executable,
-    or False if the executable is not present """
+def _get_exe_version_output(exe, args):
     try:
         # STDIN should be redirected too. On UNIX-like systems, ffmpeg triggers
         # SIGTTOU if yt-dlp is run in the background.
@@ -4022,7 +4019,7 @@ def get_exe_version(exe, args=['--version'],
         return False
     if isinstance(out, bytes):  # Python 2.x
         out = out.decode('ascii', 'ignore')
-    return detect_exe_version(out, version_re, unrecognized)
+    return out
 
 
 def detect_exe_version(output, version_re=None, unrecognized='present'):
@@ -4036,6 +4033,14 @@ def detect_exe_version(output, version_re=None, unrecognized='present'):
         return unrecognized
 
 
+def get_exe_version(exe, args=['--version'],
+                    version_re=None, unrecognized='present'):
+    """ Returns the version of the specified executable,
+    or False if the executable is not present """
+    out = _get_exe_version_output(exe, args)
+    return detect_exe_version(out, version_re, unrecognized) if out else False
+
+
 class LazyList(collections.abc.Sequence):
     ''' Lazy immutable list from an iterable
     Note that slices of a LazyList are lists and not LazyList'''