当我尝试实例化这个结构时,我的程序崩溃了:
struct MemoryAVFormat {
MemoryAVFormat(const MemoryAVFormat &) = delete;
AVFormatContext *ctx;
AVIOContext *ioCtx;
MemoryAVFormat(char *audio, size_t audio_length) :
ctx(avformat_alloc_context()),
ioCtx(create_audio_buffer_io_context(audio, audio_length)) {
if (ctx == nullptr)
throw audio_processing_exception("Failed to allocate context");
if (ioCtx == nullptr)
throw audio_processing_exception("Failed to allocate IO context for audio buffer");
ctx->pb = ioCtx;
ctx->flags |= AVFMT_FLAG_CUSTOM_IO;
int err = avformat_open_input(&ctx, "nullptr", NULL, NULL);
if (err != 0)
throwAvError("Error configuring context from audio buffer", err);
}
AVIOContext *create_audio_buffer_io_context(char *audio, size_t audio_length) const {
return avio_alloc_context(reinterpret_cast<unsigned char *>(audio),
audio_length,
0,
audio,
[](void *, uint8_t *, int buf_size) { return buf_size; },
NULL,
NULL);
}
~MemoryAVFormat() {
av_free(ioCtx);
avformat_close_input(&ctx);
}
}
我已经阅读并尝试了每一个关于这样做的教程,但它们都不起作用有没有人以前做过这个工作?
在线崩溃:
int err = avformat_open_input(&ctx, "nullptr", NULL, NULL);
最佳答案
avio_alloc_context()
文档指定 buffer
参数应由 av_malloc()
分配,而且它将由 AVIOContext
析构函数释放并且可以随时重新分配:
* @param buffer Memory block for input/output operations via AVIOContext.
* The buffer must be allocated with av_malloc() and friends.
* It may be freed and replaced with a new buffer by libavformat.
* AVIOContext.buffer holds the buffer currently in use,
* which must be later freed with av_free().
在您的代码示例中,您省略了 audio
缓冲区分配的详细信息,但我认为它不符合这些要求,因此当 FFmpeg 尝试释放或重新分配 audio
缓冲区时会发生崩溃。我猜想将整个音频文件内容作为外部分配的缓冲区传递不会与
AVIOContext
一起使用 - 这个 API 真的是要与临时缓冲区一起使用,用于从其他地方(文件、Web 或其他内存缓冲区)流式传输数据。我没有完整的示例来查看它是否会按预期工作,但代码可能看起来像这样(您可能需要调整
read()
函数并考虑实现 seeking procedure):struct MemoryAVFormat {
MemoryAVFormat(const MemoryAVFormat &) = delete;
AVFormatContext *ctx;
AVIOContext *ioCtx;
char *audio;
size_t audio_length;
size_t audio_offset;
MemoryAVFormat(char *theAudio, size_t theAudioLength)
: ctx(avformat_alloc_context()),
ioCtx(nullptr),
audio(theAudio),
audio_length(theAudioLength),
audio_offset(0) {
ioCtx = create_audio_buffer_io_context();
if (ctx == nullptr)
throw audio_processing_exception("Failed to allocate context");
if (ioCtx == nullptr)
throw audio_processing_exception("Failed to allocate IO context for audio buffer");
ctx->pb = ioCtx;
ctx->flags |= AVFMT_FLAG_CUSTOM_IO;
int err = avformat_open_input(&ctx, "nullptr", NULL, NULL);
if (err != 0)
throwAvError("Error configuring context from audio buffer", err);
}
int read (uint8_t* theBuf, int theBufSize) {
int aNbRead = std::min (int(audio_length - audio_offset), theBufSize);
if(aNbRead == 0) { return AVERROR_EOF; }
memcpy(theBuf, audio + audio_offset, aNbRead);
audio_offset += aNbRead;
return aNbRead;
}
int64_t seek(int64_t offset, int whence) {
if (whence == AVSEEK_SIZE) { return audio_length; }
audio_offset = offset;
if(audio == NULL || audio_length == 0) { return -1; }
if (whence == SEEK_SET) { audio_offset = offset; }
else if(whence == SEEK_CUR) { audio_offset += offset; }
else if(whence == SEEK_END) { audio_offset = audio_length + offset; }
//if(audio_offset < 0) { audio_offset = 0; } else
//if(audio_offset > audio_length) { audio_offset = audio_length; }
return offset;
}
AVIOContext *create_audio_buffer_io_context() {
const int aBufferSize = 4096;
unsigned char* aBufferIO = (unsigned char* )av_malloc(aBufferSize + AV_INPUT_BUFFER_PADDING_SIZE);
return avio_alloc_context(aBufferIO,
aBufferSize,
0,
this,
[](void* opaque, uint8_t* buf, int bufSize)
{ return ((MemoryAVFormat* )opaque)->read(buf, bufSize); },
NULL,
[](void* opaque, int64_t offset, int whence)
{ return ((MemoryAVFormat* )opaque)->seek(offset, whence); });
}
~MemoryAVFormat() {
av_free(ioCtx);
avformat_close_input(&ctx);
}
}
实现 AVIOContext
接口(interface)和使用 avformat_open_input()
的替代方法可以是将音频缓冲区作为自定义 AVPacket
的有效负载直接传递给解码器,如果您事先知道您的流是哪种音频格式(例如,完全跳过 AVFormatContext
的创建)。我这样做是为了解码图像像素图,但不知道它是否可以(轻松)应用于音频。
关于c++ - FFMPEG 从内存中读取音频不起作用,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/66003356/