Add --hls-use-mpegts option

When using the mpegts container hls vidoes can be played while being downloaded (useful if you are recording a live stream).
VLC and mpv play them file, but QuickTime doesn't.

youtube_dl/YoutubeDL.py

@@ -263,7 +263,7 @@ class YoutubeDL(object):
     the downloader (see youtube_dl/downloader/common.py):
     nopart, updatetime, buffersize, ratelimit, min_filesize, max_filesize, test,
     noresizebuffer, retries, continuedl, noprogress, consoletitle,
-    xattr_set_filesize, external_downloader_args.
+    xattr_set_filesize, external_downloader_args, hls_use_mpegts.
 
     The following options are used by the post processors:
     prefer_ffmpeg:     If True, use ffmpeg instead of avconv if both are available,

youtube_dl/__init__.py

@@ -369,6 +369,7 @@ def _real_main(argv=None):
         'no_color': opts.no_color,
         'ffmpeg_location': opts.ffmpeg_location,
         'hls_prefer_native': opts.hls_prefer_native,
+        'hls_use_mpegts': opts.hls_use_mpegts,
         'external_downloader_args': external_downloader_args,
         'postprocessor_args': postprocessor_args,
         'cn_verification_proxy': opts.cn_verification_proxy,

youtube_dl/downloader/common.py

@@ -45,6 +45,7 @@ class FileDownloader(object):
                         (experimental)
     external_downloader_args:  A list of additional command-line arguments for the
                         external downloader.
+    hls_use_mpegts:     Use the mpegts container for HLS videos.
 
     Subclasses of this one must re-define the real_download method.
     """

youtube_dl/downloader/hls.py

@@ -39,7 +39,11 @@ class HlsFD(FileDownloader):
                 '-headers',
                 ''.join('%s: %s\r\n' % (key, val) for key, val in headers.items())]
 
-        args += ['-i', url, '-f', 'mp4', '-c', 'copy', '-bsf:a', 'aac_adtstoasc']
+        args += ['-i', url, '-c', 'copy']
+        if self.params.get('hls_use_mpegts', False):
+            args += ['-f', 'mpegts']
+        else:
+            args += ['-f', 'mp4', '-bsf:a', 'aac_adtstoasc']
 
         args = [encodeArgument(opt) for opt in args]
         args.append(encodeFilename(ffpp._ffmpeg_filename_argument(tmpfilename), True))

youtube_dl/options.py

@@ -415,6 +415,11 @@ def parseOpts(overrideArguments=None):
         '--hls-prefer-native',
         dest='hls_prefer_native', action='store_true',
         help='Use the native HLS downloader instead of ffmpeg (experimental)')
+    downloader.add_option(
+        '--hls-use-mpegts',
+        dest='hls_use_mpegts', action='store_true',
+        help='Use the mpegts container for HLS videos, allowing to play the '
+             'video while downloading (some players may not be able to play it')
     downloader.add_option(
         '--external-downloader',
         dest='external_downloader', metavar='COMMAND',