On 27/12/2019 13:05, Ralph Corderoy wrote:
...
VLC has no choice but to play the single audio stream in the MP4 file.
Whether technical or audiodescribed, there is only one audio stream
present.
...
So I don't know how VLC is avoiding reading out the audio descriptions
unless it's not actually an audiodescribed download that was obtained.
get_iplayer could obtain both audio streams and put them in one MP4 file
along with the video, and VLC and other players could then present the
choice of audiodescribed or not, just as foreign-language dubbing is
sometimes present in non-iPlayer material.
Hi Ralph
It could, but it doesn't, and as you say there is only one audio stream
in the .mp4 file created by get_iplayer. I don't use audio described
but I do download material which is not on the iPlayer from my satellite
receiver. A typical film from Channel 4 HD had, according to the Tools
Codec tab in VLC
Stream 0 H.264 video 1920x1080 25fps
Stream 1 MPEG Audio layer 1/2 Language NAR stereo 192kbit/s
Stream 2 English Teletext subtitles
Stream 3 English DVB subtitles
Stream 4 A52 Audio (aka AC3) Language English
NAR is short for Narrative and is the equivalent of audio described. On
VLC's Audio Audio Track menu there are three radio buttons
Disable
Track 1 [NAR]
Track 2 [English]
Track 1 is selected by default, and it plays a stereo sound track with
audio description. If Track 2 is selected, it plays the AC3 5.1
surround sound track but there is no audio description. That seems to
me to confirm what you say, that VLC will ONLY play audio description if
the audiodescribed version has been downloaded.
A thought has occurred to me. All the references have been to DVF modes
and for DVF audio and video are downloaded separately. Is it possible
for the video to have been downloaded from a default, original or
technical version while the audio has been taken from an audiodescribed
version? I have not managed to find where in the Perl script
get_iplayer decides which audio and video streams to download, so I
don't know the answer.
Best wishes
Richard
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