class RawVideoWriter

template <bool enabled = true>

class RawVideoWriter

Defined at line 53 of file ../../src/media/lib/raw_video_writer/raw_video_writer.h

This class enables a client to easily create and write raw uncompressed video

frames to a file. The frames can be played back using a tool like this:

mplayer -demuxer rawvideo -rawvideo w=320:h=240:format=nv12

The file itself does not have any format metadata associated, so is only

playable with a command such as the above if the format + size is known or

guessed OOB. Limited ability to write uint32_t to the file is provided but

use of these is discouraged if all the frames are the same format.

The source data is allowed to provide the data in format-specific ways when

it comes to things like stride, offset to UV plane(s), etc. Each format has

a separate Write_.*() method to allow this class to pack the pixel data into

the file without gaps.

Callers will want to write all the same frame size and same format, but this

is not enforced currently. Playing back a file with a mix of frame sizes and

formats isn't a thing.

After creating the RawVideoWriter object, Initialize() must be called exactly

once before invoking other methods. If nullptr or "" is passed to Initialize

(instead of a valid file name), a default file path+name of

'/tmp/raw_video_writer_N.wav' is used, where N is an integer corresponding to

the instance of RawVideoWriter running in that process.

Following Initialize, an appropriate Write method is used to append a video

frame to the file. Once the client has completely written the file, the

client should call Close to close the file.

An instance of the class is single-use.

An instance is thread compatible but not thread safe. The client bears all

responsibilities for synchronization. Call from only one thread at a time,

with adequate happens-before between calls. The global "N" allocator is

thread-safe.

Appending frames is only supported in one format per object instance.

Public Methods

void RawVideoWriter<enabled> (const char * file_name)

Default of nullptr uses /tmp/raw_video_writer_N.wav, where N is unique only

per instance in this process.

A file is opened lazily by the first write call, to avoid creating an empty

file if no writes occur.

Defined at line 28 of file ../../src/media/lib/raw_video_writer/raw_video_writer.cc

void ~RawVideoWriter<enabled> ()

Will call Close()

Defined at line 38 of file ../../src/media/lib/raw_video_writer/raw_video_writer.cc

bool IsOk ()

IsOk()

Is the file still ok after the writes so far?

Calling this is entirely optional. The failure model here is stateful in

the sense that we don't try to write more to the file after a previous

open/write to the file fails.

Defined at line 45 of file ../../src/media/lib/raw_video_writer/raw_video_writer.cc

size_t WriteUint32BigEndian (uint32_t number)

WriteUint32BigEndian() / WriteUint32LittleEndian()

Escape hatch for writing ad-hoc file header / frame header info. Currently

this is mostly here to establish a pattern of caring about endian-ness for

any such escape hatches, just to force consideration of which endian-ness

we actually intend to have in the file (not to have an opinion on which

choice is best).

The return value is 4, always. A return of 4 does not imply that the write

succeeded - for that see IsOk().

BigEndian - Write in big-endian to the file regardless of where this code

is running.

LittleEndian - Write in little-endian to the file regardless of where this

code is running.

Defined at line 50 of file ../../src/media/lib/raw_video_writer/raw_video_writer.cc

size_t WriteUint32LittleEndian (uint32_t number)

Defined at line 58 of file ../../src/media/lib/raw_video_writer/raw_video_writer.cc

size_t WriteNv12 (uint32_t width_pixels, uint32_t height_pixels, uint32_t stride, const uint8_t * y_base, uint32_t uv_offset)

Write an NV12 format frame.

The return value is the number of bytes implied by the input parameters

always, regardless of write success/failure. For write success/failure see

IsOk().

The y_base default of nullptr calculates and returns the count of bytes

that would be written to the file without actually writing them.

The uv_offset is effectively optional - if 0 is specified (via default or

explicitly), the uv_offset used is height_pixels * stride.

width_pixels - Y width - must be even, at least for now. There are this

many pixels width of Y data, and half this many pixels width of U and

V data.

height_pixels - Y height - must be even, at least for now. There are

this many lines of Y data, and half this many lines of UV data.

stride - NV12 uses the same stride for Y and UV together. This is the

offset from Y start-of-line to next Y start-of-line, and the offset

from UV start-of-U-then-V-line to next start-of-U-then-V-line.

y_base - pointer to first byte of first pixel of Y plane, or nullptr if

the call is just supposed to calculate how many bytes would have been

written.

uv_offset - the bytes offset from y_base to first byte of first pixel of

U data.

Defined at line 66 of file ../../src/media/lib/raw_video_writer/raw_video_writer.cc

void Close ()

Close() finishes/closes the file. IsOk() will return true after this call

if closing worked.

Defined at line 106 of file ../../src/media/lib/raw_video_writer/raw_video_writer.cc

void Delete ()

Delete() deletes the file. IsOk() will return true after this iff the

delete worked.

Defined at line 133 of file ../../src/media/lib/raw_video_writer/raw_video_writer.cc