[FFmpeg-devel] [PATCH] avcodec: Add bits_per_raw_sample to AVCodecParameters

[wm4]

On Mon, 11 Apr 2016 13:26:54 +0200
Hendrik Leppkes <h.leppkes at gmail.com> wrote:

> On Mon, Apr 11, 2016 at 1:17 PM, wm4 <nfxjfg at googlemail.com> wrote:
> > On Mon, 11 Apr 2016 12:52:51 +0200
> > Hendrik Leppkes <h.leppkes at gmail.com> wrote:
> >  
> >> On Mon, Apr 11, 2016 at 11:29 AM, wm4 <nfxjfg at googlemail.com> wrote:  
> >> > On Mon, 11 Apr 2016 03:12:20 +0200
> >> > Michael Niedermayer <michael at niedermayer.cc> wrote:
> >> >  
> >> >> On Sun, Apr 10, 2016 at 11:39:57PM +0000, Kieran Kunhya wrote:  
> >> >> > On Mon, 11 Apr 2016 at 00:33 Michael Niedermayer <michael at niedermayer.cc>
> >> >> > wrote:
> >> >> >  
> >> >> > > The bits_per_raw_sample represents the number of bits of precission per
> >> >> > > sample.
> >> >> > >
> >> >> > > The field is added at the logical place, not at the end as the code was
> >> >> > > just
> >> >> > > recently added
> >> >> > >
> >> >> > > This fixes the regression about loosing the audio sample precission
> >> >> > > information
> >> >> > >
> >> >> > > The change in the fate test checksum un-does the change from the merge
> >> >> > >
> >> >> > > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> >> >> > > ---
> >> >> > >  libavcodec/avcodec.h |   17 +++++++++++++++++
> >> >> > >  libavcodec/utils.c   |    2 ++
> >> >> > >  tests/ref/lavf/ffm   |    2 +-
> >> >> > >  3 files changed, 20 insertions(+), 1 deletion(-)
> >> >> > >
> >> >> > > diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
> >> >> > > index b3655c5..87739d7 100644
> >> >> > > --- a/libavcodec/avcodec.h
> >> >> > > +++ b/libavcodec/avcodec.h
> >> >> > > @@ -3832,9 +3832,26 @@ typedef struct AVCodecParameters {
> >> >> > >       */
> >> >> > >      int64_t bit_rate;
> >> >> > >
> >> >> > > +    /**
> >> >> > > +     * The number of bits per sample in the codedwords.
> >> >> > > +     *
> >> >> > > +     * This is basically the bitrate per sample
> >> >> > > +     *
> >> >> > > +     * This could be for example 4 for ADPCM
> >> >> > > +     * For PCM formats this matches bits_per_raw_sample
> >> >> > > +     * Can be 0
> >> >> > > +     */
> >> >> > >      int bits_per_coded_sample;
> >> >> > >
> >> >> > >      /**
> >> >> > > +     * The number of bits of precission in the samples.
> >> >> > > +     *
> >> >> > > +     * For ADPCM this might be 12 or 16 or similar
> >> >> > > +     * Can be 0
> >> >> > > +     */
> >> >> > > +    int bits_per_raw_sample;
> >> >> > >
> >> >> > >  
> >> >> > Precision spelt wrong. Also needs more clarification as to the difference
> >> >> > between the two  
> >> >>
> >> >> on one side of a bitstream format there is raw pcm data (raw samples)
> >> >> and on the other a compressed bitstream (aka coded samples)
> >> >> these 2 where intended to specify the number of bits per sample in
> >> >> these 2 representations
> >> >>
> >> >> i really dont know how to word this so that its clear and everyone
> >> >> understands it
> >> >>
> >> >>  
> >> >> > - I have no idea what the difference is or why one would
> >> >> > use bits_per_coded_sample for anything.  
> >> >>
> >> >> bits_per_coded_sample is used by several codecs (huffyuv, ima adpcm,
> >> >> ...) in avi as a single byte extradata. so it must be transported from
> >> >> the demuxer (avi headers) to the decoder and encoder to muxer
> >> >> to make this worse, in some of these codecs it matches the
> >> >> bits_per_raw_sample, in some it does not  
> >> >
> >> > I still don't understand. bits_per_coded_sample is part of the
> >> > AVCodecParameters struct. So what's the difference between per_coded
> >> > and per_raw?
> >> >  
> >>
> >> As I understand it, coded is mandatory for a bunch of formats to
> >> actually decode it, ie. the number of bits for one sample in the
> >> actual coded bitstream.
> >> And raw is just the bits in a decoded (raw) sample. Sometimes those
> >> two can be the same, especially if the codec in question doesnt have a
> >> concept of coded bits per sample.  
> >
> > Then I don't understand why the field can't be reused.
> >
> > One thing that would have to be done though is copying the field to the
> > AVCodecContext.bits_per_raw_sample field in decoder init or so.  
> 
> How can it be reused if you practically have two values? One for
> coded, and one for raw? One is mandatory for decoding, and one is good
> to know so you can interpret S32 sample format properly.

It's only a problem if they collide, but maybe it's really better to
have them separate to avoid a potential mess.