问题描述
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,audio,[](void *,uint8_t *,int buf_size) { return buf_size; },NULL);
}
~MemoryAVFormat() {
av_free(ioCtx);
avformat_close_input(&ctx);
}
}
以前有人用过吗?
线路崩溃:int err = avformat_open_input(&ctx,NULL);
解决方法
avio_alloc_context()
文档指定 buffer
参数应该由 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 - 此 API 实际上是为了与临时缓冲区一起使用,以便从其他地方(文件、网络或另一个内存缓冲区)。
我没有完整的示例来查看它是否会按预期工作,但代码可能如下所示(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,this,[](void* opaque,uint8_t* buf,int bufSize)
{ return ((MemoryAVFormat* )opaque)->read(buf,bufSize); },int64_t offset,int whence)
{ return ((MemoryAVFormat* )opaque)->seek(offset,whence); });
}
~MemoryAVFormat() {
av_free(ioCtx);
avformat_close_input(&ctx);
}
}
实现 AVIOContext
接口和使用 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,如果您事先知道哪种音频格式您的流是(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。