Hi Kevin,
I don't know about a general reference for codec params but
here is how it is done for MP2 encoder in the FFMPEG decoding_encoding.c
example.
They generate a tone and encode it in mp2.
Maybe it could be a starting point.
All I've done with libav has been from examples. There is very little to no
documentation online.
Good luck.
____________________________________________
static void audio_encode_example(const char *filename)
{
AVCodec *codec;
AVCodecContext *c= NULL;
AVFrame *frame;
AVPacket pkt;
int i, j, k, ret, got_output;
int buffer_size;
FILE *f;
uint16_t *samples;
float t, tincr;
printf("Encode audio file %s\n", filename);
/* find the MP2 encoder */
codec = avcodec_find_encoder(AV_CODEC_ID_MP2);
if (!codec) {
fprintf(stderr, "Codec not found\n");
exit(1);
}
c = avcodec_alloc_context3(codec);
if (!c) {
fprintf(stderr, "Could not allocate audio codec context\n");
exit(1);
}
/* put sample parameters */
c->bit_rate = 64000;
/* check that the encoder supports s16 pcm input */
c->sample_fmt = AV_SAMPLE_FMT_S16;
if (!check_sample_fmt(codec, c->sample_fmt)) {
fprintf(stderr, "Encoder does not support sample format %s",
av_get_sample_fmt_name(c->sample_fmt));
exit(1);
}
/* select other audio parameters supported by the encoder */
c->sample_rate = select_sample_rate(codec);
c->channel_layout = select_channel_layout(codec);
c->channels = av_get_channel_layout_nb_channels(c->channel_layout);
/* open it */
if (avcodec_open2(c, codec, NULL) < 0) {
fprintf(stderr, "Could not open codec\n");
exit(1);
}
f = fopen(filename, "wb");
if (!f) {
fprintf(stderr, "Could not open %s\n", filename);
exit(1);
}
/* frame containing input raw audio */
frame = av_frame_alloc();
if (!frame) {
fprintf(stderr, "Could not allocate audio frame\n");
exit(1);
}
frame->nb_samples = c->frame_size;
frame->format = c->sample_fmt;
frame->channel_layout = c->channel_layout;
/* the codec gives us the frame size, in samples,
* we calculate the size of the samples buffer in bytes */
buffer_size = av_samples_get_buffer_size(NULL, c->channels, c->frame_size,
c->sample_fmt, 0);
if (buffer_size < 0) {
fprintf(stderr, "Could not get sample buffer size\n");
exit(1);
}
samples = av_malloc(buffer_size);
if (!samples) {
fprintf(stderr, "Could not allocate %d bytes for samples buffer\n",
buffer_size);
exit(1);
}
/* setup the data pointers in the AVFrame */
ret = avcodec_fill_audio_frame(frame, c->channels, c->sample_fmt,
(const uint8_t*)samples, buffer_size, 0);
if (ret < 0) {
fprintf(stderr, "Could not setup audio frame\n");
exit(1);
}
/* encode a single tone sound */
t = 0;
tincr = 2 * M_PI * 440.0 / c->sample_rate;
for (i = 0; i < 200; i++) {
av_init_packet(&pkt);
pkt.data = NULL; // packet data will be allocated by the encoder
pkt.size = 0;
for (j = 0; j < c->frame_size; j++) {
samples[2*j] = (int)(sin(t) * 10000);
for (k = 1; k < c->channels; k++)
samples[2*j + k] = samples[2*j];
t += tincr;
}
/* encode the samples */
ret = avcodec_encode_audio2(c, &pkt, frame, &got_output);
if (ret < 0) {
fprintf(stderr, "Error encoding audio frame\n");
exit(1);
}
if (got_output) {
fwrite(pkt.data, 1, pkt.size, f);
av_free_packet(&pkt);
}
}
/* get the delayed frames */
for (got_output = 1; got_output; i++) {
ret = avcodec_encode_audio2(c, &pkt, NULL, &got_output);
if (ret < 0) {
fprintf(stderr, "Error encoding frame\n");
exit(1);
}
if (got_output) {
fwrite(pkt.data, 1, pkt.size, f);
av_free_packet(&pkt);
}
}
fclose(f);
av_freep(&samples);
av_frame_free(&frame);
avcodec_close(c);
av_free(c);
}
Le 18 juin 2015 à 16:04, Kevin J. Brooks <[email protected]> a écrit :
> Can someone point me to a reference where I can learn how to set up the codec
> parameters? Even if it is only setting up for WMAV2, but I do need to record
> both audio and video.
>
> On 6/17/2015 5:53 PM, Kevin J. Brooks wrote:
>> I changed the Audio codec to WMAV2, and left the rest of the AudioCodec
>> settings the same Now the program crashes at this line in the QtMel code:
>>
>> int outSize = avcodec_encode_audio(m_audioStream->codec,
>> m_audioOutputBuffer, m_audioOutputBufferSize, (short *)samples.data());
>>
>> In debug the error staates "Stopped in thread 2 by:Exception at 0x66364c62,
>> cod:0xc0000005: write access violation at:0x1, flags=0x0 (first chance).
>>
>> I suspect I don't have the audio settings set write, but I am not sure how
>> to set them for WMAV2.
>>
>>
>>
>> On 6/17/2015 4:30 PM, Kevin J. Brooks wrote:
>>> I am setting the AudioCodec to MP3, I am using the pre-built libraries the
>>> code I have the causes the issue is from the code for the QtMEL library.
>>> What I am posting here is the Audio Codec setup for the QtMel object. I
>>> hope it helps.
>>>
>>> BTW I am using H264 for the Video Codec. If I record video only, it does
>>> work, it is only if I try to add sound that it fails.
>>>
>>> CR2CAudioFormat format;
>>> format.setChannelCount(2);
>>> format.setSampleRate(44100);
>>> format.setFormat(CR2CAudioFormat::SignedInt16);
>>>
>>> I really don't have a preference for the codec, I just need to know how to
>>> set it up properly. I am totally new at recording video and audio.
>>>
>>> On 6/17/2015 1:08 AM, Taha Ansari wrote:
>>>> On Wed, Jun 17, 2015 at 2:17 AM, Gonzalo Garramuno <[email protected]>
>>>> wrote:
>>>> On 16/06/15 09:06, Kevin J. Brooks wrote:
>>>> Yes I am. For more information, I am developing on Windoze 7.
>>>> avcodec_open2 can fail if you lack the library for the codec you want to
>>>> decode or encode. For example, libx264. The libraries in
>>>> ffmpeg.zeranoe.com contain all codecs, but they are GPL only. You should
>>>> try them first and see if the problem goes away. If it does, you know you
>>>> have to compile ffmpeg with different flags.
>>>>
>>>> Since he mentions Windows 7, I assume he is using pre-built packages from
>>>> zeranoe site (as you mention). These builds contain proprietary codec(s)
>>>> like x264 (non GPL).
>>>>
>>>> @Kevin: maybe you have some bare minimum code with you that can produce
>>>> this error, which people can have a look?
>>>>
>>>>
>>>> _______________________________________________
>>>> Libav-user mailing list
>>>> [email protected]
>>>> http://ffmpeg.org/mailman/listinfo/libav-user
>>>
>>>
>>>
>>> _______________________________________________
>>> Libav-user mailing list
>>> [email protected]
>>> http://ffmpeg.org/mailman/listinfo/libav-user
>>
>>
>>
>> _______________________________________________
>> Libav-user mailing list
>> [email protected]
>> http://ffmpeg.org/mailman/listinfo/libav-user
>
> _______________________________________________
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> [email protected]
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