Setting a bit
Use the bitwise OR operator (|
) to set a bit.
number |= 1UL << n;
That will set the n
th bit of number
. n
should be zero, if you want to set the 1
st bit and so on upto n-1
, if you want to set the n
th bit.
Use 1ULL
if number
is wider than unsigned long
; promotion of 1UL << n
doesn't happen until after evaluating 1UL << n
where it's undefined behaviour to shift by more than the width of a long
. The same applies to all the rest of the examples.
Clearing a bit
Use the bitwise AND operator (&
) to clear a bit.
number &= ~(1UL << n);
That will clear the n
th bit of number
. You must invert the bit string with the bitwise NOT operator (~
), then AND it.
Toggling a bit
The XOR operator (^
) can be used to toggle a bit.
number ^= 1UL << n;
That will toggle the n
th bit of number
.
Checking a bit
You didn't ask for this, but I might as well add it.
To check a bit, shift the number n to the right, then bitwise AND it:
bit = (number >> n) & 1U;
That will put the value of the n
th bit of number
into the variable bit
.
Changing the nth bit to x
Setting the n
th bit to either 1
or 0
can be achieved with the following on a 2's complement C++ implementation:
number ^= (-x ^ number) & (1UL << n);
Bit n
will be set if x
is 1
, and cleared if x
is 0
. If x
has some other value, you get garbage. x = !!x
will booleanize it to 0 or 1.
To make this independent of 2's complement negation behaviour (where -1
has all bits set, unlike on a 1's complement or sign/magnitude C++ implementation), use unsigned negation.
number ^= (-(unsigned long)x ^ number) & (1UL << n);
or
unsigned long newbit = !!x; // Also booleanize to force 0 or 1
number ^= (-newbit ^ number) & (1UL << n);
It's generally a good idea to use unsigned types for portable bit manipulation.
or
number = (number & ~(1UL << n)) | (x << n);
(number & ~(1UL << n))
will clear the n
th bit and (x << n)
will set the n
th bit to x
.
It's also generally a good idea to not to copy/paste code in general and so many people use preprocessor macros (like the community wiki answer further down) or some sort of encapsulation.
In my experience you should give FFMPEG the least amount of information when initialising your codec as possible. This may seem counter intuitive but it means that FFMPEG will use it's default settings that are more likely to work than your own guesses. See what I would include below:
AVStream *stream;
m_video_codec = avcodec_find_encoder(AV_CODEC_ID_H264);
stream = avformat_new_stream(_outputCodec, m_video_codec);
ctx = stream->codec;
ctx->codec_id = m_fmt->video_codec;
ctx->bit_rate = m_AVIMOV_BPS; //Bits Per Second
ctx->width = m_AVIMOV_WIDTH; //Note Resolution must be a multiple of 2!!
ctx->height = m_AVIMOV_HEIGHT; //Note Resolution must be a multiple of 2!!
ctx->time_base.den = m_AVIMOV_FPS; //Frames per second
ctx->time_base.num = 1;
ctx->gop_size = m_AVIMOV_GOB; // Intra frames per x P frames
ctx->pix_fmt = AV_PIX_FMT_YUV420P;//Do not change this, H264 needs YUV format not RGB
As in previous answers, here is a working example of the FFMPEG library encoding RGB frames to a H264 video:
http://www.imc-store.com.au/Articles.asp?ID=276
An extra thought on your code though:
Have a look at the linked example, I tested it on VC++2010 and it works perfectly.
Best Answer
Don't forget to use x264 private options. You can always set a profile:
Or set the lowest encoding latency:
Or select a preset:
Before opening a codec