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

[Hendrik Leppkes]

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.

- Hendrik