On 2024-01-28 04:24 pm, Anton Khirnov wrote:
Quoting Gyan Doshi (2024-01-26 05:23:50)
On 2024-01-25 06:47 pm, Andreas Rheinhardt wrote:
Gyan Doshi:
On 2024-01-25 10:29 am, Andreas Rheinhardt wrote:
Gyan Doshi:
Set up framework for non-PCM decoding in-place and
add support for Dolby-E decoding.
Useful for direct transcoding of non-PCM audio in live inputs.
---
configure | 1 +
doc/decoders.texi | 40 +++
libavcodec/s302m.c | 609 +++++++++++++++++++++++++++++++++++++--------
3 files changed, 543 insertions(+), 107 deletions(-)
diff --git a/configure b/configure
index c8ae0a061d..8db3fa3f4b 100755
--- a/configure
+++ b/configure
@@ -2979,6 +2979,7 @@ rv20_decoder_select="h263_decoder"
rv20_encoder_select="h263_encoder"
rv30_decoder_select="golomb h264pred h264qpel mpegvideodec rv34dsp"
rv40_decoder_select="golomb h264pred h264qpel mpegvideodec rv34dsp"
+s302m_decoder_select="dolby_e_decoder"
screenpresso_decoder_deps="zlib"
shorten_decoder_select="bswapdsp"
sipr_decoder_select="lsp"
diff --git a/doc/decoders.texi b/doc/decoders.texi
index 293c82c2ba..9f85c876bf 100644
--- a/doc/decoders.texi
+++ b/doc/decoders.texi
@@ -347,6 +347,46 @@ configuration. You need to explicitly configure
the build with
An FFmpeg native decoder for Opus exists, so users can decode Opus
without this library.
+@section s302m
+
+SMPTE ST 302 decoder.
+
+SMPTE ST 302 is a method for storing AES3 data format within an MPEG
Transport
+Stream. AES3 streams can contain LPCM streams of 2, 4, 6 or 8
channels with a
+bit depth of 16, 20 or 24-bits at a sample rate of 48 kHz.
+They can also contain non-PCM codec streams such as AC-3 or Dolby-E.
+
This sounds like we should add bitstream filters to extract the proper
underlying streams instead.
(I see only two problems with this approach: The BSF API needs to set
the CodecID of the output during init, but at this point no packet has
reached the BSF to determine it. And changing codec IDs mid-stream is
also not supported.)
In theory, this decoder shouldn't exist, as it is just a carrier,
whether of LPCM or non-PCM.
FFmpeg architecture also imposes a fundamental limitation in that one
s302m stream may
carry multiple payload streams and we support only one decoding context
per input stream
Then why does the demuxer not separate the data into multiple streams?
I didn't add demuxing support for this codec in MPEGTS, but I can venture
a) it would mean essentially inlining this decoder in the demuxer.
Why is that a problem? This decoder seems like it shouldn't be a
decoder.
I agree with Andreas that this seems like it's a demuxer pretending to
be a decoder.
This module transforms the entire raw payload data to generate its
output, even if the syntax is simple which
essentially makes it a de-coder. The de-multiplexer aspect of multiple
streams is an academic possibility allowed
by the standard but not seen in any sample which makes me suspect it's
used for carriage between broadcast
facilities rather than something ever sent to an OTT provider, let alone
an end user.
Regards,
Gyan
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