[Libav-user] I can't get audio decoding to work.

[Bill Messenger]

This is the function I'm using to decode the audio file. My guess is that
it's crashing because "dataSize" is larger than "frame->data[0]", but I'm
pretty sure my calculation of dataSize is correct. Am I copying the frame
data to "sampleBuffer" the wrong way?

bool AudioDecoder::decodeFile(std::string* filename)
{
reset(); // if a file has already been decoded, free it from memory and
reset

AVFormatContext* formatCtx = avformat_alloc_context();
if(avformat_open_input(&formatCtx, filename->c_str(), nullptr, nullptr) < 0)
{
wxGetApp().popUpErrorDialog("Couldn't open \"" + *filename + "\".");
avformat_close_input(&formatCtx);
return false;
}

if(avformat_find_stream_info(formatCtx, nullptr) < 0)
{
wxGetApp().popUpErrorDialog("Couldn't find file info for \"" + *filename +
"\".");
avformat_close_input(&formatCtx);
return false;
}

av_dump_format(formatCtx, 0, filename->c_str(), false);

int streamID = -1;
for(int i = 0; i < formatCtx->nb_streams; i++)
{
if(formatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO)
{
streamID = i;
break;
}
}
if(streamID == -1)
{
wxGetApp().popUpErrorDialog("\"" + *filename + "\" does not contain
audio.");
avformat_close_input(&formatCtx);
return false;
}

AVCodecContext* codecCtx = formatCtx->streams[streamID]->codec;
AVCodec* codec = avcodec_find_decoder(codecCtx->codec_id);
if(!codec)
{
wxGetApp().popUpErrorDialog("Couldn't find the codec for \"" + *filename +
"\".");
avformat_close_input(&formatCtx);
return false;
}
if(avcodec_open2(codecCtx, codec, nullptr) < 0)
{
wxGetApp().popUpErrorDialog("Couldn't open the codec for\"" + *filename +
"\".");
avformat_close_input(&formatCtx);
return false;
}

sampleFormat = codecCtx->sample_fmt;
if(!(sampleFormat == AV_SAMPLE_FMT_U8 || sampleFormat == AV_SAMPLE_FMT_U8P
||
sampleFormat == AV_SAMPLE_FMT_S16 || sampleFormat == AV_SAMPLE_FMT_S16P ||
sampleFormat == AV_SAMPLE_FMT_S32 || sampleFormat == AV_SAMPLE_FMT_S32P ||
sampleFormat == AV_SAMPLE_FMT_FLT || sampleFormat == AV_SAMPLE_FMT_FLTP ||
sampleFormat == AV_SAMPLE_FMT_DBL || sampleFormat == AV_SAMPLE_FMT_DBLP))
{
wxGetApp().popUpErrorDialog("\"" + *filename + "\" uses an unsupported
format.");
avcodec_close(codecCtx);
avformat_close_input(&formatCtx);
return false;
}

planar = false;
if(sampleFormat == AV_SAMPLE_FMT_U8P || sampleFormat == AV_SAMPLE_FMT_S16P
||
  sampleFormat == AV_SAMPLE_FMT_S32P || sampleFormat == AV_SAMPLE_FMT_FLTP
|| sampleFormat == AV_SAMPLE_FMT_DBLP)
{
planar = true;
}

AVFrame* frame = av_frame_alloc();
if(!frame)
{
wxGetApp().popUpErrorDialog("Failed to allocate an audio frame.");
avcodec_close(codecCtx);
avformat_close_input(&formatCtx);
return false;
}

AVPacket packet;
av_init_packet(&packet);

duration = formatCtx->duration / (double)AV_TIME_BASE; // duration is
defined in AudioDecoder.h as "double duration = 0;"

uint64_t estimatedBuffSize = std::ceil(duration * codecCtx->sample_rate *
av_get_bytes_per_sample(codecCtx->sample_fmt) * codecCtx->channels);

sampleBuffer = (uint8_t*)std::malloc(estimatedBuffSize); // sampleBuffer is
defined in AudioDecoder.h as "uint8_t* sampleBuffer = nullptr;"
sampleBufferSet = true;

int len;
int gotFrame = 0;
uint64_t dataSize;
uint64_t totalBufferSize = 0;
uint64_t totalSamples = 0;
while(av_read_frame(formatCtx, &packet) == 0)
{
len = avcodec_decode_audio4(codecCtx, frame, &gotFrame, &packet);
if(len < 0)
{
wxGetApp().popUpErrorDialog("Error while decoding.");
std::free(sampleBuffer);
sampleBufferSet = false;
av_packet_unref(&packet);
av_frame_free(&frame);
avcodec_close(codecCtx);
avformat_close_input(&formatCtx);
return false;
}

if(gotFrame)
{
dataSize = av_samples_get_buffer_size(nullptr, codecCtx->channels,
frame->nb_samples, codecCtx->sample_fmt, 1);

while(totalBufferSize + dataSize > estimatedBuffSize)
{
estimatedBuffSize *= 1.1;
sampleBuffer = (uint8_t*)std::realloc(sampleBuffer, estimatedBuffSize);
}

std::memcpy(sampleBuffer + totalBufferSize, frame->data[0], dataSize);

totalBufferSize += dataSize;
totalSamples += frame->nb_samples;
}

av_packet_unref(&packet);
}

sampleBuffer = (uint8_t*)std::realloc(sampleBuffer, totalBufferSize);

numChannels = codecCtx->channels;
sampleRate = codecCtx->sample_rate;
numSamples = totalSamples;
bufferSize = totalBufferSize;

av_packet_unref(&packet);
av_frame_free(&frame);
avcodec_close(codecCtx);
avformat_close_input(&formatCtx);

didInit = true;

return true;
}

On Fri, Jun 17, 2016 at 4:20 PM, Bill Messenger <apothemmusic at gmail.com>
wrote:

> Update: I found out that it only crashes in debug mode. When I build it in
> release mode, it doesn't crash. It must be a bug in MSVC 2015 or something.
>
> On Fri, Jun 17, 2016 at 4:06 PM, Bill Messenger <apothemmusic at gmail.com>
> wrote:
>
>> I'm trying to create a class that uses FFmpeg to decode any audio file
>> and store it into memory. Then it has a function that returns a float value
>> of any sample in that buffer. The code I wrote works perfectly for wav and
>> flac files, produces weird audio for mp3 and ogg files, and crashes on
>> certain mp3 files. I spent days trying to figure out why it isn't working,
>> but I can't come up with anything.
>>
>> I think the reason why the audio is weird for mp3 and ogg files is that
>> it uses planar audio instead of interleaved audio, but I don't see what's
>> wrong with the code I wrote. I may be missing something though. For
>> example, to get a sample for 16 bit interleaved audio I use:
>>
>> int16_t tmp = ((int16_t*)sampleBuffer)[numChannels*sample + channel];
>> rv = (float)tmp / 32767.0f;
>>
>> and to get a sample for 16 bit planar audio I use:
>>
>> int16_t tmp = ((int16_t*)sampleBuffer)[sample + numSamples*channel];
>> rv = (float)tmp / 32767.0f;
>>
>> And I have no clue why it crashes on certain mp3 files. I paid close
>> attention to make sure there is enough memory allocated in the buffer.
>> What's even weirder is that the file I created "Chiptune 15 2.mp3" didn't
>> crash, but when I renamed it to "test.mp3", it crashed! These crashes
>> happen on line 139 of "AudioDecoder.cpp":
>>
>> std::memcpy(sampleBuffer + totalBufferSize, frame->extended_data[0],
>> dataSize);
>>
>> with an "Access violation reading location" error in vcruntime140d.dll.
>> It says it isn't with location 0x0000000000000000 or 0xFFFFFFFFFFFFFFFF
>> though, it's a different random location.
>>
>> I attached a zip file with the c++ code and two mp3's. Oh yeah, I should
>> also mention that I'm using MSVC 2015 Community in Windows 10.
>>
>
>
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