[FFmpeg-devel] [PATCH 1/2] spdifenc: IEC 61937 encapsulation of DTS-HD for HDMI

[Måns Rullgård]

Anssi Hannula <anssi.hannula at iki.fi> writes:

> On 27.01.2011 19:50, Justin Ruggles wrote:
>> Hi,
>
> Hi!
>
>> On 01/21/2011 01:32 PM, Anssi Hannula wrote:
>> 
>>> ---
>>>
>>> This time the default mode of operation is to passthrough DTS-core only
>>> unless the HD mode is explicitely requested by the user via an AVOption.
>>>
>>> This way we avoid exporting the final bitrate in avctx->bit_rate as I
>>> previously planned, as now the caller always specifies the output rate
>>> themselves and therefore already knows the output rate (as is the case
>>> for other formats as well).
>>>
>>> An AVOption is used instead of the previously planned muxrate as the
>>> usage doesn't exactly match muxrate semantics.
>>>
>>>  Changelog              |    2 +-
>>>  libavformat/avformat.h |    2 +-
>>>  libavformat/spdifenc.c |  147 ++++++++++++++++++++++++++++++++++++++++++++++++
>>>  3 files changed, 149 insertions(+), 2 deletions(-)
>>>
>>> +static int spdif_header_dts4(AVFormatContext *s, AVPacket *pkt, int core_size,
>>> +                             int sample_rate, int blocks)
>>> +{
>>> +    IEC61937Context *ctx = s->priv_data;
>>> +    const char dtshd_start_code[10] = { 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xfe, 0xfe };
>> 
>> 
>> dtshd_start_code could be made static.
>
> Hm, what difference would it make?
>
> Since it is a constant, the values are retained over calls by definition
> even without "static" keyword, and indeed there seems to be no
> difference between "const" or "static const" inside a function in output
> of gcc.

It does make a difference:

---8<---
int baz(const char *);

int foo(void)
{
    const char x[] = { 1, 2, 3, 4 };
    return baz(x);
}

int bar(void)
{
    static const char x[] = { 1, 2, 3, 4 };
    return baz(x);
}
--->8---

Disassembly of section .text:

00000000 <foo>:
   0:   e52de004        push    {lr}            ; (str lr, [sp, #-4]!)
   4:   e59f301c        ldr     r3, [pc, #28]   ; 28 <foo+0x28>
   8:   e24dd00c        sub     sp, sp, #12
   c:   e5933000        ldr     r3, [r3]
  10:   e28d0008        add     r0, sp, #8
  14:   e5203004        str     r3, [r0, #-4]!
  18:   ebfffffe        bl      0 <baz>
  1c:   e28dd00c        add     sp, sp, #12
  20:   e49de004        pop     {lr}            ; (ldr lr, [sp], #4)
  24:   e12fff1e        bx      lr
  28:   00000000        .word   0x00000000

0000002c <bar>:
  2c:   e92d4008        push    {r3, lr}
  30:   e59f0008        ldr     r0, [pc, #8]    ; 40 <bar+0x14>
  34:   ebfffffe        bl      0 <baz>
  38:   e8bd4008        pop     {r3, lr}
  3c:   e12fff1e        bx      lr
  40:   00000004        .word   0x00000004

-- 
M?ns Rullg?rd
mans at mansr.com