[Ffmpeg-devel] [PATCH] RTP payload format for AMR

[Michael Niedermayer]

Hi

On Wed, Mar 07, 2007 at 09:00:11PM +0530, Kite Flyer wrote:
> Hi,
> 
> My work required to stream AMR audio. The attached patch implements
> octet-aligned payload for AMR NB mono audio as per RFC 3267. It works well
> with several media players e.g. real player, QuickTime player etc.
> 
> I could very well change the bit rate with "-ab" option using older SVN
> code. But current SVN code (ffmpeg.c) seems to break the option. Any idea
> how to set the audio bit rate now?

-ab 123 is now -ab 123k or kb


[...]

> +        //TODO: find a way to pack maximum number of frames based on max_payload_size 

yes


[...]
>      }
>  }
>  
> +/* Send AMR audio. Note: AMR_NB, single channel is supported now. */
> +static void rtp_send_amr(AVFormatContext *s1,
> +                               const uint8_t *buf1, int size)
> +{
> +    RTPDemuxContext *s = s1->priv_data;
> +    AVStream *st = s1->streams[0];
> +    const static uint8_t packed_size[16] = {12, 13, 15, 17, 19, 20, 26, 31, 5, 0, 0, 0, 0, 0, 0, 0};
> +    uint8_t toc, ft;
> +    int dlen;
> +
> +    if (st->codec->codec_id != CODEC_ID_AMR_NB)
> +        return; //FIXME: clean if reqd
> +
> +    if (size < 1)
> +        return;
> +
> +    /* correct table of contents and add frames */
> +    while (size > 0) {

this function cannot receive more then 1 frame at a time, if it does then
there is a bug somewhere, (if the amr encoder outputs several frames
concatenated then it is buggy, if a demuxer outputs such mess a AVParser
is needed to split it up, reimplementing such split up code everywhere
will not be accepted)


[...]
> +#ifdef DEBUG
> +            printf("AMR: incomplete frame: frame type = %d, data len=%d, size = %d\n", ft, dlen, size);
> +            //FIXME check if the data would come in next chunk
> +#endif

please use dprintf() insetad of printf under #ifdef DEBUG


> +        }
> +
> +        /* flush if max number of frames added */
> +        //TODO: find a way to pack maximum number of frames
> +        if (s->frame_count == AMR_NB_MAX_FRAMES)
> +        {
> +            s->buf[s->frame_count] &= 0x7f; // set f = 0
> +            rtp_send_data(s1, s->buf, s->buf_ptr - s->buf, 0);
> +            s->timestamp += 160 * s->frame_count;
> +            s->buf[0] = 0xf0;
> +            memset(s->buf + 1, 0x7c, AMR_NB_MAX_FRAMES);

what does this memset do? isnt the area always overwritten again?


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I am the wisest man alive, for I know one thing, and that is that I know
nothing. -- Socrates
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