2023-04-04：使用 Golang 和 ffmpeg-go 库实现 demuxing_decoding.c，轻松掌握音视频分离解码技巧。
答案2023-04-05：
使用github/moonfdd/ffmpeg-go库。
代码使用FFmpeg库打开一个音视频文件，提取其中的视频和音频流，并解码每一帧数据。它将解码后的视频和音频帧写入不同的输出文件中。代码中使用了libavformat、libavcodec和libavutil库提供的函数。
大体过程如下：
1.设置FFmpeg库的路径。
2.打开音视频文件并分配AVFormatContext结构体。
3.获取音频和视频流的信息，并选择合适的解码器进行解码。
4.对于视频流：
分配AVCodecContext结构体。
设置解码器参数并打开解码器。
读取视频帧并进行解码。
将解码后的视频帧写入输出文件。
5.对于音频流：
分配AVCodecContext结构体。
设置解码器参数并打开解码器。
读取音频帧并进行解码。
将解码后的音频帧写入输出文件。
6.关闭解码器和输入输出文件句柄，释放内存。
命令如下：
go run ./examples/internalexamples/demuxing_decoding/main.go ./resources/big_buck_bunny.mp4 ./out/big_buck_bunny.yuv ./out/big_buck_bunny.pcm
./lib/ffplay -f rawvideo -pix_fmt yuv420p -video_size 640x360 ./out/big_buck_bunny.yuv
./lib/ffplay -f f32le -ac 1 -ar 22050 .\out\big_buck_bunny.pcm
代码如下：
package main
import (
"fmt"
"os"
"unsafe"
"github.com/moonfdd/ffmpeg-go/ffcommon"
"github.com/moonfdd/ffmpeg-go/libavcodec"
"github.com/moonfdd/ffmpeg-go/libavformat"
"github.com/moonfdd/ffmpeg-go/libavutil"
)
func main0() (ret ffcommon.FInt) {
if len(os.Args) != 4 {
fmt.Printf("usage: %s input_file video_output_file audio_output_file\nAPI example program to show how to read frames from an input file.\nThis program reads frames from a file, decodes them, and writes decoded\nvideo frames to a rawvideo file named video_output_file, and decoded\naudio frames to a rawaudio file named audio_output_file.\n",
os.Args[0])
os.Exit(1)
}
src_filename = os.Args[1]
video_dst_filename = os.Args[2]
audio_dst_filename = os.Args[3]
/* open input file, and allocate format context */
if libavformat.AvformatOpenInput(&fmt_ctx, src_filename, nil, nil) < 0 {
fmt.Printf("Could not open source file %s\n", src_filename)
os.Exit(1)
}
/* retrieve stream information */
if fmt_ctx.AvformatFindStreamInfo(nil) < 0 {
fmt.Printf("Could not find stream information\n")
os.Exit(1)
}
for {
if open_codec_context(&video_stream_idx, &video_dec_ctx, fmt_ctx, libavutil.AVMEDIA_TYPE_VIDEO) >= 0 {
video_stream = fmt_ctx.GetStream(uint32(video_stream_idx))
video_dst_file, _ = os.Create(video_dst_filename)
if video_dst_file == nil {
fmt.Printf("Could not open destination file %s\n", video_dst_filename)
ret = 1
break
}
/* allocate image where the decoded image will be put */
width = video_dec_ctx.Width
height = video_dec_ctx.Height
pix_fmt = video_dec_ctx.PixFmt
ret = libavutil.AvImageAlloc(&video_dst_data, &video_dst_linesize,
width, height, pix_fmt, 1)
if ret < 0 {
fmt.Printf("Could not allocate raw video buffer\n")
break
}
video_dst_bufsize = ret
}
if open_codec_context(&audio_stream_idx, &audio_dec_ctx, fmt_ctx, libavutil.AVMEDIA_TYPE_AUDIO) >= 0 {
audio_stream = fmt_ctx.GetStream(uint32(audio_stream_idx))
audio_dst_file, _ = os.Create(audio_dst_filename)
if audio_dst_file == nil {
fmt.Printf("Could not open destination file %s\n", audio_dst_filename)
ret = 1
break
}
}
/* dump input information to stderr */
fmt_ctx.AvDumpFormat(0, src_filename, 0)
if audio_stream == nil && video_stream == nil {
fmt.Printf("Could not find audio or video stream in the input, aborting\n")
ret = 1
break
}
frame = libavutil.AvFrameAlloc()
if frame == nil {
fmt.Printf("Could not allocate frame\n")
ret = -libavutil.ENOMEM
break
}
pkt = libavcodec.AvPacketAlloc()
if pkt == nil {
fmt.Printf("Could not allocate packet\n")
ret = -libavutil.ENOMEM
break
}
if video_stream != nil {
fmt.Printf("Demuxing video from file '%s' into '%s'\n", src_filename, video_dst_filename)
}
if audio_stream != nil {
fmt.Printf("Demuxing audio from file '%s' into '%s'\n", src_filename, audio_dst_filename)
}
/* read frames from the file */
for fmt_ctx.AvReadFrame(pkt) >= 0 {
// check if the packet belongs to a stream we are interested in, otherwise
// skip it
if pkt.StreamIndex == uint32(video_stream_idx) {
ret = decode_packet(video_dec_ctx, pkt)
} else if pkt.StreamIndex == uint32(audio_stream_idx) {
ret = decode_packet(audio_dec_ctx, pkt)
}
pkt.AvPacketUnref()
if ret < 0 {
break
}
}
/* flush the decoders */
if video_dec_ctx != nil {
decode_packet(video_dec_ctx, nil)
}
if audio_dec_ctx != nil {
decode_packet(audio_dec_ctx, nil)
}
fmt.Printf("Demuxing succeeded.\n")
if video_stream != nil {
fmt.Printf("Play the output video file with the command:\nffplay -f rawvideo -pix_fmt %s -video_size %dx%d %s\n",
libavutil.AvGetPixFmtName(pix_fmt), width, height,
video_dst_filename)
}
if audio_stream != nil {
sfmt := audio_dec_ctx.SampleFmt
n_channels := audio_dec_ctx.Channels
var fmt0 string
if libavutil.AvSampleFmtIsPlanar(sfmt) != 0 {
packed := libavutil.AvGetSampleFmtName(sfmt)
if packed == "" {
packed = "?"
}
fmt.Printf("Warning: the sample format the decoder produced is planar (%s). This example will output the first channel only.\n",
packed)
sfmt = libavutil.AvGetPackedSampleFmt(sfmt)
n_channels = 1
}
ret = get_format_from_sample_fmt(&fmt0, sfmt)
if ret < 0 {
break
}
fmt.Printf("Play the output audio file with the command:\nffplay -f %s -ac %d -ar %d %s\n",
fmt0, n_channels, audio_dec_ctx.SampleRate,
audio_dst_filename)
}
break
}
// end:
libavcodec.AvcodecFreeContext(&video_dec_ctx)
libavcodec.AvcodecFreeContext(&audio_dec_ctx)
libavformat.AvformatCloseInput(&fmt_ctx)
if video_dst_file != nil {
video_dst_file.Close()
}
if audio_dst_file != nil {
audio_dst_file.Close()
}
libavcodec.AvPacketFree(&pkt)
libavutil.AvFrameFree(&frame)
libavutil.AvFree(uintptr(unsafe.Pointer(video_dst_data[0])))
if ret < 0 {
return 1
} else {
return 0
}
}
var fmt_ctx *libavformat.AVFormatContext
var video_dec_ctx, audio_dec_ctx *libavcodec.AVCodecContext
var width, height ffcommon.FInt
var pix_fmt libavutil.AVPixelFormat
var video_stream, audio_stream *libavformat.AVStream
var src_filename string
var video_dst_filename string
var audio_dst_filename string
var video_dst_file *os.File
var audio_dst_file *os.File
var video_dst_data [4]*ffcommon.FUint8T
var video_dst_linesize [4]ffcommon.FInt
var video_dst_bufsize ffcommon.FInt
var video_stream_idx, audio_stream_idx ffcommon.FInt = -1, -1
var frame *libavutil.AVFrame
var pkt *libavcodec.AVPacket
var video_frame_count ffcommon.FInt
var audio_frame_count ffcommon.FInt
func output_video_frame(frame *libavutil.AVFrame) ffcommon.FInt {
if frame.Width != width || frame.Height != height ||
frame.Format != pix_fmt {
/* To handle this change, one could call av_image_alloc again and
* decode the following frames into another rawvideo file. */
fmt.Printf("Error: Width, height and pixel format have to be constant in a rawvideo file, but the width, height or pixel format of the input video changed:\nold: width = %d, height = %d, format = %s\nnew: width = %d, height = %d, format = %s\n",
width, height, libavutil.AvGetPixFmtName(pix_fmt),
frame.Width, frame.Height,
libavutil.AvGetPixFmtName(frame.Format))
return -1
}
fmt.Printf("video_frame n:%d coded_n:%d\n",
video_frame_count, frame.CodedPictureNumber)
video_frame_count++
/* copy decoded frame to destination buffer:
* this is required since rawvideo expects non aligned data */
libavutil.AvImageCopy(&video_dst_data, &video_dst_linesize,
(*[4]*byte)(unsafe.Pointer(&frame.Data)), (*[4]int32)(unsafe.Pointer(&frame.Linesize)),
pix_fmt, width, height)
/* write to rawvideo file */
video_dst_file.Write(ffcommon.ByteSliceFromByteP(video_dst_data[0], int(video_dst_bufsize)))
return 0
}
func output_audio_frame(frame *libavutil.AVFrame) ffcommon.FInt {
unpadded_linesize := ffcommon.FSizeT(frame.NbSamples * libavutil.AvGetBytesPerSample(libavutil.AVSampleFormat(frame.Format)))
fmt.Printf("audio_frame n:%d nb_samples:%d pts:%s\n",
audio_frame_count, frame.NbSamples,
libavutil.AvTs2timestr(frame.Pts, &audio_dec_ctx.TimeBase))
audio_frame_count++
/* Write the raw audio data samples of the first plane. This works
* fine for packed formats (e.g. AV_SAMPLE_FMT_S16). However,
* most audio decoders output planar audio, which uses a separate
* plane of audio samples for each channel (e.g. AV_SAMPLE_FMT_S16P).
* In other words, this code will write only the first audio channel
* in these cases.
* You should use libswresample or libavfilter to convert the frame
* to packed data. */
audio_dst_file.Write(ffcommon.ByteSliceFromByteP(*frame.ExtendedData, int(unpadded_linesize)))
return 0
}
func decode_packet(dec *libavcodec.AVCodecContext, pkt *libavcodec.AVPacket) ffcommon.FInt {
ret := ffcommon.FInt(0)
// submit the packet to the decoder
ret = dec.AvcodecSendPacket(pkt)
if ret < 0 {
fmt.Printf("Error submitting a packet for decoding (%s)\n", libavutil.AvErr2str(ret))
return ret
}
// get all the available frames from the decoder
for ret >= 0 {
ret = dec.AvcodecReceiveFrame(frame)
if ret < 0 {
// those two return values are special and mean there is no output
// frame available, but there were no errors during decoding
if ret == libavutil.AVERROR_EOF || ret == -libavutil.EAGAIN {
return 0
}
fmt.Printf("Error during decoding (%s)%d\n", libavutil.AvErr2str(ret), ret)
return ret
}
// write the frame data to output file
if dec.Codec.Type == libavutil.AVMEDIA_TYPE_VIDEO {
ret = output_video_frame(frame)
} else {
ret = output_audio_frame(frame)
}
frame.AvFrameUnref()
if ret < 0 {
return ret
}
}
return 0
}
func open_codec_context(stream_idx *ffcommon.FInt,
dec_ctx **libavcodec.AVCodecContext, fmt_ctx *libavformat.AVFormatContext, type0 libavutil.AVMediaType) ffcommon.FInt {
var ret, stream_index ffcommon.FInt
var st *libavformat.AVStream
var dec *libavcodec.AVCodec
var opts *libavutil.AVDictionary
ret = fmt_ctx.AvFindBestStream(type0, -1, -1, nil, 0)
if ret < 0 {
fmt.Printf("Could not find %s stream in input file '%s'\n",
libavutil.AvGetMediaTypeString(type0), src_filename)
return ret
} else {
stream_index = ret
st = fmt_ctx.GetStream(uint32(stream_index))
/* find decoder for the stream */
dec = libavcodec.AvcodecFindDecoder(st.Codecpar.CodecId)
if dec == nil {
fmt.Printf("Failed to find %s codec\n",
libavutil.AvGetMediaTypeString(type0))
return -libavutil.EINVAL
}
/* Allocate a codec context for the decoder */
*dec_ctx = dec.AvcodecAllocContext3()
if *dec_ctx == nil {
fmt.Printf("Failed to allocate the %s codec context\n",
libavutil.AvGetMediaTypeString(type0))
return -libavutil.ENOMEM
}
/* Copy codec parameters from input stream to output codec context */
ret = (*dec_ctx).AvcodecParametersToContext(st.Codecpar)
if ret < 0 {
fmt.Printf("Failed to copy %s codec parameters to decoder context\n",
libavutil.AvGetMediaTypeString(type0))
return ret
}
/* Init the decoders */
ret = (*dec_ctx).AvcodecOpen2(dec, &opts)
if ret < 0 {
fmt.Printf("Failed to open %s codec\n",
libavutil.AvGetMediaTypeString(type0))
return ret
}
*stream_idx = stream_index
}
return 0
}
func get_format_from_sample_fmt(fmt0 *string, sample_fmt libavutil.AVSampleFormat) (ret ffcommon.FInt) {
switch sample_fmt {
case libavutil.AV_SAMPLE_FMT_U8:
*fmt0 = "u8"
case libavutil.AV_SAMPLE_FMT_S16:
*fmt0 = "s16le"
case libavutil.AV_SAMPLE_FMT_S32:
*fmt0 = "s32le"
case libavutil.AV_SAMPLE_FMT_FLT:
*fmt0 = "f32le"
case libavutil.AV_SAMPLE_FMT_DBL:
*fmt0 = "f64le"
default:
fmt.Printf("sample format %s is not supported as output format\n",
libavutil.AvGetSampleFmtName(sample_fmt))
ret = -1
}
return
}
func main() {
os.Setenv("Path", os.Getenv("Path")+";./lib")
ffcommon.SetAvutilPath("./lib/avutil-56.dll")
ffcommon.SetAvcodecPath("./lib/avcodec-58.dll")
ffcommon.SetAvdevicePath("./lib/avdevice-58.dll")
ffcommon.SetAvfilterPath("./lib/avfilter-56.dll")
ffcommon.SetAvformatPath("./lib/avformat-58.dll")
ffcommon.SetAvpostprocPath("./lib/postproc-55.dll")
ffcommon.SetAvswresamplePath("./lib/swresample-3.dll")
ffcommon.SetAvswscalePath("./lib/swscale-5.dll")
genDir := "./out"
_, err := os.Stat(genDir)
if err != nil {
if os.IsNotExist(err) {
os.Mkdir(genDir, 0777) // Everyone can read write and execute
}
}
main0()
}
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